UNIVERSITY OF ALBERTA

Microclimate and geomorphic tesponses to wildfïre in a subarctic upland focest

undedain by permaftost

Jérôme-Etienne Lesemana O

-1 thesis submitted to the Faculn- of Graduate Studies and Research in paraai ~ ~ e n t

of the requirements for the degree of Master of Saence

Department of Eartb and Atmospheric Sciences

Edmonton, -ilberta

Fail 1998

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-4 study was undu<aken ro assess the post-tire irecrodLnate and geomorphic responses of a

subarcric upland forest underlain by permafro- f i e study sire uas a simdated a n s p o r t corridor

located near Tulira, NYT. Microdimate data were collected for air and soi1 cemperarures, uGid

speed relative humidity. ndiaaon Buses and snoupack characterkacs. Soil cores 1%-ere used for

texture and moisnire content andysis. -\ctn~e Iayer depth w a s measured by the probing method.

S d a c e subsidence was assessed using topographie levellig techniques and ground p e n e t r a ~ g radar.

In burned treannmts tree canop- removal and surface aibedo lowering led to increases in ner

radiation and warmer soi1 tempemures. Post-6re snoupacks were thinner and denser chan pre-fke

values. Soil moisure decreased afrer rue. Post-fue ïncrease in actil-e layer depth and seasonal/long

c m subsidence uas inrersely proportional ro die degree and age of the disturbance. Subsidence and

thaw depth were masimal in die trench. right-of-way and burned forest respecrively.

Thesis wking is seidom a solitaq- effort and this one is no exception. -A number of

peopIe have helped me in many ways. 1 hope 1 don'r forget aqone. 1 must k t t h d my

superrisor Dr. G.P. Kershaw for larchmg me onto this proiect, h r his contagous enthusiasm in

fieid work and for bringrng my core body temperature doun to leveis O+- experieaced by ice

cream, polar bean and dead arctic esqdorers! His help in data coiietion during surnmer and

&ter outings =-as much appreciated as was his prompt r e m of my chapters during the 1 s t

throws of the thesis. Sfembers of my superrisory cornmittee. Dr. John England and Dr. Ross

Wein. aiacailr assessed my work and made valuable suggesaons to irnprore the thesis.

Khile workiog at the "ashtray", Wendy Davis (somehow uillingly) helped during winter

snow sarnpling- She u a s aiso a good &end to vent' \rith when diings went wrong. Steuaff

Brown wxs a grear camp mate and selflessb- helped in the topographic sweying and data

collection. Jens Walther and Josh Bylik also shared in camp life and helped with the GPR sun-ms.

To ai of ou, thanks and here's to 'radio bingo'.

Bea and Blair Jensen of Crsus ;\vïaaon provided hne air charter senice to and from the

research site. Their help extended weii beyond the Tulira air scrip as they freely offered warm

showers and a fiiendlt. roice on the radio. Interprovinaal Pipelines (IPL) helped in the logistics

by generously proxidlig heiicopter lifts to and from the camp. Dr. lohn Shaw free- ienr out his

Ground Penetraung Radar and offered encouragement. Funding for this research was protided

br NSERC (operathg grant to Dr. G.P. Kershaw) and through an NSTP (Northern Saenufic

Training Program) award to the author from the Canadian Circumpolar Insarute.

-At the University of -liberta a number of people made deparunent life fun. Rob Young

and .\lanna Vernon are thanked for th& abundant contribuaon to the 'ked trough' and for just

iistening. -1nthony -Arendt took rime to heIp with rniaoclimare and cornputer \klzardn-. H e also

read and suggested changes to some chapters. Xfandy and Dave. Claire, Rod, Sreuart, Wendy,

Darren, Kim, Josh, .\nthonv and Brian ail made office Me more interesting. The Joki clan is

thanked for their friendship. fruitcakes and phone calls and for p r o d i n g a haven where

academic insanity has no meaning.

Finaily, I hare ro thank my parents and f d - for their encouragement and support.

They have always let me choose my o m path and have unconditionally supponed my choices

Gom chasing horses to permafrost.

Table of Contents

Chapter 1: Introduction, site descriptions, thesis objectives and thesis outiine.

Introduction 1

Ptevious pst-fire investigations in permafrost terrain - 7

-Effects of buming on microciimatic conditions - 3

-Changes in seasonal thaw depth and surface subsidence - 7

-Effeas of snow accumulation on ground temperatures and acEire layer thickness 3

-Influence of vegetation col-er on permafrost distribuaon 3

Site Description

-Geology and soils

-Clhate

-Vegetaaon

Structure of thesis and research objectives

References

Chapter 2: Microclimatic responses of a subarctic upland forest foiiowing wiidnre.

Introduction 17

Objectives

Factors affecting permafrost and the ground thermal regime

-Re-fire (undisturbed) e n q - eschanges and permafrost equilibrium

-Effects of vegctation on the radiation budget and the ground thermal r e p e

-Effects of snowpack characrerisocs on the ground thennai t e e

-Pos t-£ire energy exchanges and e ffects on permafrost equilibrium

Methods

- & f i a o h t e

-Snow course measutements

-Data anal+

Theory

-Components of the radiauon budget

Results

-AL temperature and degree index cdculaaons

-Relaare humidity

-n'"id speed

-Radiation budget

Inroming sholt-rvrlire radution

,\'rl a//-wutr r&tttan

-Radiation budger cornparisons beween bumed and control ueatrnenrs

-Soil temperatures

-Snowpack characteristics

Snonprlck 4th Jnorvplrck I12?n~z4.

-Diffaences in snowpack deprh and den si^ beween burned and conrrol treau-nents

- H a t Trans fer Coeffiaen t (HTC)

RO Ir- Bumed f i m f Jnd h a h g edge des

-Re- rs. post-fxe differences in HTC

-Cornparison of pre- rs. port-Gre HTC values with conrrol ueaunent

Discussion

-Radianon budget cornparisons berneen bumed and conuol treaanents

Short-rime rudiution and d b e h

Long-wrlzr mdirltion

,\-et rudation

-Snompack deprh

Confmf tmtment

Bumed jom

,\-orfb-~outh orienttd RO II--

h i - w e ~ t otiented RO Il"

-Snowpack densin-

Contml twtmznt

T m p o r t Lï)rn'dor

- H a t Trans fer Coet'liaent and sod temperames

-Pre- rs. posr-fie cornparisons of HTC values

Conclusion

References

Chapter 3: Soi1 properties and thaw depth foliowing wiidfire in a subarctic upland

forest and on a simuiated aaaspoa corridor.

Introduction

Objectives

Post-fire modifications of the active fayer

Post-fire modifications of soi1 moisture contents

Field methods

- Fms t pro bing

-Soil coring

Labotatory methods

-hioisnue and texnire analysis

-S tatisâcal anaiysis

Results

-Seasonai post-6re moisnue content and differences from die control treament

-Pre- vs. post-tire changes in moisnire content

-Post-hre seasonal variauons in mean maximum thau- deph

-Pre- rs. post-tire mriauons in mean masimum tham depth

Discussion

-Pre- rs. port-6re changes in mean moisme content

P o ~ t y h dfferen~w in rnoi~*tzm mrfenf bthveen tTputmentr

Poifjin d$eirnm- in moi~~tz~ir iontent between br,md md "ontmi' irnrltmnti

-Re- rs. posr-tre varîaaons in thau- depth

Bmned-/omt

hghtj- q ' w a

Tm'be~-

-Spatial rariaaon of thau- deprh and influence of microsite characteristics

Conclusion

References

Chapter 4: T hermokars t subsidence and seasonal/long-terni terrain modifications

foilowing wildfire and anthropogenic disnubance.

Introduction

-Surface subsidence on iinear disturbances

-Ground penetrating radar as a cool for geophysicai intesagations

Objectives

Methods

-Topographie sun-ey

-Ground penetraung radar

Data pmcessing

-Topographie data

-Statis ticai anal+

-Ground penenating radar

-Ground penemting radar interpretaaon techniques

Results

-Seasonai su bsidence

Conpunion tvithin tre~tmrnt~

-Total subsidence since 1790

-Totai surface subsidence since clearïng (1 986)

-Ground penetrating radar

Bwnedjore~~t J H R * ~ J -

RO tl" mnVg s

Discussion

-Surface subsidence

Jeasonal subsi&nce

Tord sub~-iaènt-e

Conclusion

References

Chapter 5: Conclusions

-~licrociimatic reçponses to wildfrre

-Sad moisrure and actire layer thau- deprh modifications FoUoubig uildftre

-Thmakarst and surface subsidence folloning uildhe

-Future avenues of research

References

List of Tables

Table 2-1 bIean air temperarure differences and standard d k a o n s between the

control and burned meatments at heights of A) 150 cm and B) 10 cm.

&kasurement periods indude the '%inter" period before snowmdt

Oulian Davs 50- 11 5) and weekly segments for die sest of the measwement

period. The period berween Julian Days 163-2û-t is missing due ro sensor

malhncaon. ,ill temperatures are in O C -

TabIe 2-2 1997 degree indes calculations for the SEEDS and control treatments. The 28

data period used for calcuiaüons is Gom Julian Days 5 1 - 1 G1 (FDI) and 304-

"7 (-rDr). -.

Table 2-3 \Yeei+- averages of radiation budget componenrs for che Burned Forest.

ROW and Control treatments during the 1997 measurement period. -4.U

radiation fluses are in K' m 2.

Table 2-4 Surnrnary of Februan- 1997 A) Snowpack depth characteristics and B)

snowpack densin characterisucs associated wîth die SEEDS simuiaced

transport corridor. Depth and densin- given in cm and Kg m.' respectk-ely

Table 3-1 1997 post-lire mean moiscure content for the SEEDS treaunents and the

control ueaunent.

Table 3-2 1997 posr-fire differences in moisnue content (O O) benveen the burned

treaunents and the control at racious depths.

Table 3-3 Mean maximum thaw depth, standard da-iation, yearly increase and total

increase since 1986 for the SEEDS ueaunents. Data from 1986- 1990 are

from Nolte (1991). 1991-1 <)96 are from Kershaw (unpublishedj.

Table 3-4 Results of t-lpst cornparing rhaw depths of each bumed ueament for die

years 1996-1897. Wues are ln (nut~mi log.) transfomeci. 1996 data are from

Kers haw (unpu blis hed).

Table 3-5 --L\-O I :-1 resuits comparing 1997 mean maximum thaw depths among

Burned Forest. ROW. Trench and Controt treaunents. Taiues are in (nafami

log.) trans formed.

Table 3-6 Muitiple cornparison test (TJIR~' 5 tes/) for pairs of mean maximum thaw depths 71

in the three buned ueaanents (Burned Forest, ROKI Trench) and the ConuoI

treaunent. -UI cornparisons are based on in (nut~ira/ hg.) tram formed data.

Table 4-1 >lean 1997 surface subsidence for the Burned Forest RO\Y. Trench, Seisrnic 91

Line and Controi treannents. Subsidence in cm.

Table 4-2 Resuits of Pairuise Muitiple Cornparison Procedure berneen rreaanents using 91

Dunn > .\ lhod

Table 4-3 Among treatment descriptive staciscics of 1997 seasonal subsidence for the 93

Burned Forest, ROU' and Trench ueaunents.

Table 4-4 Results of One-\S-ay .\nalysis of l'ariance on Ranks among ueaunents 93

Table 4-5 Mean total surface subsidence since the Iasr topographic sun-ey (1390) F o l t e 94

1991) for the Burned Forest. ROC' and Trench treaments. Subsidence in cm.

Table 4-6 biean surface subsidence since the last topographie sun-ey (1990) vo l te 1931) 94

u-ithin each treatment n-pe at the SEEDS site. Subsidence in cm.

Table 4-7 hfean rota1 surface subsidence since the 1986 clearîng of the Burned Forest. 95

R O W and Trench treatments at the SEEDS site (Nolte 1991;. Subsidence in cm.

List of Figures

Figure 1-1 Location map of rhe SEEDS (Studie~ of'tbe EmimnmentuI EfeLitr of DrCt~~rbrlnrpr 5

in the Subrln~itj research site (Kershaw 199 1). The h d e t of Fort-Norman is

now c d e d Tuiita ("Where the waters meet").

Figurel-2 SEEDSs~datedcransportcomdorui1386-198~.-~~soiCndr~-ttlrbed~~o~~-t 6

are non- refened to as burned toresr. Source: Kershau- (1986).

Figure 2-1 Snowpack sampling sites on the simulated uansporc corridor, SEEDS. T d m 22

MIT- Sampling sites have been categorized as burned forest (sites 1.2. 10. 11,

31.39 21 and 26)- uansport corridor (sites 3.1. 5. 6. 7 , 8. 13, 13, 16. 17. 18, 19,

30 and 23) and leading edge of fores t (sites 9. 14. 15 and 25) (Iiershaw 199 1).

Figure 2-2 1997 au temperature measurements at standard heïghts for -4) Control

treaunent B) B m e d Forest treaunent, C) Trench ueaunent and D) R O K

uemnent.

Figure 2-3 1997 relatil-e humidity measured at 150 cm in .-\) Burned Forest treaunenr

B) ROW ueaunent. C) Trench ueaunent and D) Conuol treament.

Figure 2-4 1987 mean da& \r-ind speed measured at tu-O standard heights in -\) R O K 31

treaunent. B) Burned Forest ueaunent and C) Conuol treatment. Vïnd speeds

include a programmed offset ofO.U7 m s-1. L m e breaks are due to dara gaps.

Figure 2-5 1997 mean daily short-wave energ'. Bus components for the ROW. Burned 32

Forest and Concrol treaunents; -+) Incoming short-ware radiation, B) Outgoing

short-wave radiation, C) -Ubedo (calculateci). Line breaks are due ro data gaps.

Figure 2-6 1997 long-wave and net en- flm cornponents for the RO\X. Burned Forest 34

and Conuol nearmencs; -\) Calculared incoming long-=XI-e radiation.

B) Xhdeled outgohg long-wave radiation. C ) Net radiation. Line breaks are

due to data gaps.

Figure 2-7 Radiation fluxes and energ). pamtioning over the ROW, Bumed Forest and

Conuol treatmen ts for the measuremenr period beween J ulian Days 1 56- 1 63

(6June-11 June 1997).

Figure 2-8 1997 mean monthk soi1 temperature profles for the four SEEDS treaunenrs.

Figure 2-9 Comparison of mean .i) p o s t - k . Februq- 1997 snoapack depth and densin.

and B) pre-tire. F e b ~ a n - 1986- 1989 s n o ~ a c k depth and density (Kershau-

1991) on a simulated transport comdor. Ker- to locaaons: - (burned)

foresr upuind of righrs-of-way (ROK]; (B)R\X - (burned) \ es t edge of no&-

south-oriented ROW; (B)RC - @umed) center posiaon on north-south-oriented

RO\X; (B)ST - (bumed) no&- south-orienred simulated pipeline uench;

(B)RE - (burned) east edge of no&-souch-onented ROK: @)FE - (bumed)

leading edge of forest on east side of north-south-oriented ROW or south side

of east-west-orienred ROK'.

Figure 2-10 Diilerences in depth and densin- benveen snowpacks on. or affected by a

simuiated vansport corridor and an undisrurbed Forest in ;\) post-he

conditions ( F e b v 1997) and B) pre-fire conditions (February 1986-1989).

See capuon Figure 9-9 for explanaaon of locauon.

Figure 2-11 A) Comparison O f htur u/mnn~ièr 'vefi'ient (HTC) values benveen snowpacks on. 44

or affected or affecred by. a simulated uansporr corridor d h g pre-fie

conditions (1986- 1989) ( Kershau- 199 1) and post-tire conditions (1997.

B) Differences in HTC values bem-een snowpacks on. or affected by. a

simulated uansport corridor and an undisnirbed Forest during pre-tire

conditions (1 986- 1989) (Kershaw 199 1) and pos t - f ~ e conditions (2997).

Figure 3- 1 Permafrost probe (nght) and pemiafrost/temperantre probe (left)

used in 1997 to masure thau- depth.

Figure 3-2 1997 post-6re mean soi1 moisture contenrs in A) Burned Forest treamenc, 64

B) ROW creatment C) Ttench ueatment and D) Control creamient. Circles

represent mean values and error bars represent standard deriation.

Figure 3-3 Differences in mean moiscure contents benveen 1990 (Nolte 199 1) and 1997 69

for the SEEDS treaunents.

Figure 3-4

Figure 4-1

Figure 4-2

Figure 4-3

Figure 4-4

Figure 4-5

Figure 4-6

Mid--4ugust thau- depth at the SEEDS site during the w o post-ke years of- 70

measurement. Plotted values are al-eraged over the ru-O probe mnsects. 1996

dara are from Kershaw (unpublished).

Map of SEEDS research site and location of Ground Peneuating Radar

(GPR) mnsects. XIodified from Kershaw (1 991).

Colour-classed. hill shaded digital elet-auon model of 1997 seasonal

subsidence at SEEDS.

Colour-dassed. hdl-shaded digitai elevation model of total surface subsidence 96

since the miaal consuuction/clearing disturbance (1986) at SEEDS.

Radar proue from the Bumed Forest treaunent. Note the ~ ~ S C O ~ M U O U S

ground-wave reflection €rom dry hummock rops. the low tlucniauons in the

depth of the >d redector (2-2.5 m depth) and. the u-eak signal €rom the 3"'

retlector (-3.5 rn depth).

Radar protiles from the ROK' treatrnent. A) Note the signal disappearance

from lower reflector (traces 355362.5). B) Note weak signal from lower

reflector (traces 16-35).

Radar profile from the Trench treatment. Xote the down-dipping Pd and 100

3d reflectors and the chaotic r e m below 3.5 m.

Figure 4-7 Radar profle from the Trench meaurient Note possible subsidence of the 101

ground belou- -2.5 m as weU as the absence O 3" reilmor in the middie of

the trench.

Figure 4-8 Radar profle across the seismic h e (traces 319-327) located wesr of the

SEEDS site. Xote the sporadic r e m of the ground-uxe. the suong

signal from second reflector (presumed to be a grave1 lem) and che faint

r e m s from the 10- refleaor.

Chapter 1: Introduction, site descriptions, thesis objectives and thesis outiine

Introduction:

-4 growing body of iiteranxre essts c o n c e q pennafiost and nonhern development. The

study of enrironmenral disturbances and their effecn on permafrost ternuis and ecos!-stems has

received groaïng artenaon. The main bodr of literarure on this subject =-as produced dunng the later

pan of the 1960's and up to the middle of the 1970's. Ir coinaded and u n s Wrely driven bv the

ùicrease in northern development. the proposals for hydrocarbon derelopment and transport

corridors and the nurnerous northern exploration proiects that were iniaated during this penod. The

rnajorig of 'benchmark' iiteranue on die subject was wrinen during this cime.

Disturbance studies in the Subarctic have focused on the m-O main types of perturbations

that a n affect permafrost areas: anthropogenic disnirbances and n a d disturbances. During the

peak of nonhern development, it was q u i c e r e c o p e d that the presence of pemiafrost and

particukrly the presence of thaw-susceptible ice-Üch substrates, presented unique problems for

engmeerïng. .hthropogenic disnirbances, such as the consmiction of roads. pipeline corridors and

buildings were studied estensively and much has been Iearned on the construction and remediation

techniques necessari- for consmction on permafrost terrain (Broun 1970. Wright 1981).

The smdy of narural disnirbances has been ongoing but the body of lirerature on the subiecr

is much less voluminous than that associated uith geotechnical engïneenng. One obrious reason for

dus disparin- is the periodicity of these n a d - occurring fi-enrs and the logisrical compiexities

associated sith northern research. The main focii of n a d disturbance studies have been river

flooding riereck 1973) and uildGres (Hegpbottom 1973. hIaclra- 1968.1995. Viereck 1082).

.Uthough there is uidespread Literanire on lorest &es in Lie Subarctic. rnosr hare focused on the

biological effects rather than the abiouc/physical effects that also induce biological change.

Benchmark smdies have been done on the long-rem changes in permafrost after the Inutlli. SUT

tire of 1968 (BLiss and Kein 1971, Hegginbottom 1973, 1971, hlackav 1970. 1995). These snidies

constitue die majorin- of the geomorphic informarion arailable on the post-fie response of areas

underlain b?- c o n ~ u o u s permafrosr. Sirnilar, snidies hare been carried-out in areas of disconünuous

permafrost uirhin .ilaska (Hali et d. 1978. Racine 1979. Viereck 1987). There is a lack of lifonnaaon

conceming the effects (long- and shorr-rem) of wddtùps in areas of d i s con~uous permafrost

within Canada, as weil as the effects of wddhres on anthropogenic disnirbances such as mnsport

corridors.

Previous pst-fire investigations in permafrost terrain

Changes in pemiafrost are mainly the result of microdimatic variations. Degradation and

aggndation of the permafrost as weil as seasonal actire i a~e r depth is largely govemed b!- the

temperature at the ground surface and the soil hear flur (Rouse 1982. 1983. \Yeraïlliams 1982. ~ ~ i U L m s

and Smith 1989). Changes in the ground thermai regirne -di g e n d y result in flucruaaons of the

active iayer, causuig an inaease of its depth (Brown and Grave 1979, Brown and Péwé 1973.

\ K ' i i s and Smith 1989). The ground thermal regime consamtes a fragde. dynamic balance beween

vegetation. topograph y and microchate.

Effect of bumine on microclimatic conditions:

Foilouing a d d G e , the ground themial regune uill be rnodiied by the removal of

wgetation. In most cases. the heat from the tire udl not generate changes in the permafrost (Iiereck

1982. Kershau- and Rouse 1976). This is partly due to the speed at whch the tire travels and its bnef

residence &ne placta!- 1995j. The burning inrensic- is directiy proportional to the amount and

moisture content of fuel arailable. and thts is ohen scarce in Subarctic environments (Kershaw and

Rouse 1976. Liang d di. 1991). Consequendy. post-fire permafrost terrains udl otien have decreased

surface reflecuvity and increased radiation absorption forcing a marked incrase in soil temperanires

and e\-aporaaon rates (Lang d Ir:. 1991. Rouse 1976. Rouse and S U S IO7-. Haag and BLiss 19-41.

This can be coupled nith a decrease in the relative hurnidity. Increased air temperanires k o u r

higher rates ofevaporation whch tend to - the soil and alter permafrost conditions. The deaease

in relatk-e hhumidity affects the grou-th of vegetation by retardmg its regeneration. Rouse and XWs

(1976) found that absorbed solar radiation increased by 13'0 on burned sires and net long-mare

radiation loss increased by a factor of 2.3.

Changes in seasonal [ha\\- demh and surface subsidence

The ratiaaon in active l a y depth after tire is an indes of the change in the permafrost

envuonment (Liang e t d 1%) 1, Hegginbonom 1973). Increases in acul-e layer dep th have also been

associared uith the remord of regetauon (Heggmbortom 1973). increased snow accumulations

(Nicholson 1978) and the presence o i standing or running u-ater Kerfoor 1373). Ofren associated

uith variauons of rhaw depths is a change in surface morphology. Generally. thennokarst subsidence

OCCLUS as a result of the melrlig of ice-rich. thau--susceptible permafrost (French 1976.

Hegginbortom 1971. Rowe ef irl. 1973, Wein 1975). f i s m e l ~ g can be the result of an

environmental diswbance ( n a d or anthropogenk) (E\-ans tt d 1988j. Ir can also result [rom an

increase in the annual amplitude of the temperature at the ground surface. whch does not necessady

Lnpl~ a change in the mean ground temperature ~Yilliams and Smith 1989).

7 -

Quantitatkely, the amount of thaw subsidence depends on the ïncrease in thaw depth and

the amount and disrribution of pre-existing ice (French 1976, \K-iams and Smith 1989). The

thawing of ground ice inrolves a deaease of volume bu 9' o. foilou-ed by an addiaonal rolurne loss

due to drainage of melmter (Wrlliams 1982). The h a i senlement uilI be a hnction of the effective

stress between soi1 particles (kfadiay 1995). ,\dditiondv, rhermokarst subsidence can be a "self-

perpetuating" process where initial ground subsidence dou-s the entrapmenr of u-ater u-hrch favours

thawing to p r o p s deeper uiro the ground leading to hthef subsidence. Rares of subsidence d l

rary depmding on the rime suice disturbance, soii charact~stics ( d y particie skej and the rate at

which melntater is a-acuated from the soil. In Inuvdi, Hegginbonom (1971) obsen-ed a ground

subsidence of 33' O during the £ k t summer after the fke. Laboraton- tests of the same ice-rich

perrnafros t hare shown subsidence \-ar+g between 40-90° O of the onginal thickness of the frozen

material (3lackay 1995). ;\t the SEEDS site. foUo\xuig clearing, total subsidence benveen 1986 (tirne

of clearing) and 1990 u-as 31 an and 57 cm for die ROK- and Trench umtmcnits respectively (Xolte

1991).

Effects of snow accumulation on ground ternmxanires and active laver thickness

Snow has an important influence on ground temperatures because its uisuiating effect

reduces minter hear loss (Xicholson and Grandberg 19-3). The ksulauon is proportional to the

thickness of the snowpack as weU as its thermal conductivï~, which varies wich depth and densin

Wershau- 1991). Shdow snow accumulaaons offer less insulation. contriburing ro the maintenance

and/or growth of permafrost ('rlacb- 1995). Other factors also intluence ground temperature such

as substrate cexnire. soit moiscure. cegetauon cover. aspect and relief. Ttiere is a close relationshp

beween mou- depth and relief and benveen snow depth and regetation (Sicholson and Grandberg

1973). Funhermore, dense vegetauon uili creare a barrier ro winds that can scour and redistribute

snow (Kershaw 1991. Rouse 1982. 1983), enhancing the insulaaon of the ground where snow

accumulates (hluid 1981). However, snow accumulauon under uee corer is mitigated by retention by

uee branches and shmbs which can reduce the snou- cover on the ground chus Iou-ering u-inter soii

temperatures P'iereck 1965. 1973 from Tyrtikov 1959).

Influence of veeetaaon cox-er on ~errnafrost distribuaon:

Vegetation influences active Iayer depth by changmg the net radiation and the conrecuon-

conducuon relations of the surface boundary. Evaporation and transpiraaon cause a cooling of the

organic iayers due to heat dissipation (Brown 1983). Soi1 surface remperatures. subsequent to the

removal of a uee canopy can increase by 60 to 70'0. Even alter 73 years. surface temperarures can

3

rem& 30 to -K)" O u m e r than in unburned environrnents (Kershau- and Rouse 19-6). The thawuig

of the upper permafrost can compensate for the release of moisnue thar is favourable to the

regeneration of plants (Llackav 1995). Ir is speculated that as the vegetauon regenerates. the active

y e r should becorne progresskely thinner und ir m-enruatly reaches irs pre-burn thickness n'iereck

1973, 1982). Mach!- (1995) has obserred that 25 years afrer the Inuvik Eire. permafrost aggraded

causing ground uptift as a result of the aggradauon of ice.

Site description:

The smdy sire was the S/urle~ O( the E~timnrnentd E~ëitlr g' DLtitdmL-e~- NI t h SitUm-ri~- ( S E E D S )

research site (64' 58' S. 1-3' 36' \\), located approsimarely 10 km nonh of Tulita (Fort-Norman).

&PST (Figure 1-11. The SEEDS sire was esrablished in 1983 and consisted of a simuiacion of a

northern cransporr conidor (pipeiine. ainter road. htgh-tension elecrrical h e . etc.). The simulated

transport corridor \vas a hand-cleared. 690 m-long S-shaped nght-O f-way (ROK j rn a Piceu murilu

stand that burned Li lune 1995. The norch-south oriented clearings were numbered as ROWs 1. 2

and 3 from u-est to east and the connecting parts were calied North and South links (Figure 1-2). In

1985, Roi\-s 1 and 3 as weiI as the North link were cleared, and in 1986 ROK 2 and the South LLik

were added. ;\ b h e d pipeline u-as simulared b - escaratkg a 533 m-long. 1 rn-\vide and 30 cm-deep

trench u-hich \vas back-fied a i th the escai-ated minera1 and organic material Kersha\v 1988 b). The

main objectives of the SEEDS proiect \vere to coliect biouc and abiouc data pnor ro disturbance and

to monitor the effects of such a disrurbance. ,\ddttionaIly. the site was used to test and monitor

various long-tcrm teclamauon ueatments (Kershaw.1988 a). In order to assess the impacts of various

q e s of disturbances and the influence of n a m l envuonmenw1 changes. monitoring programs were

carried our in both disturbed (trenches and RO\S's) and undisturbed areas that were used as controls

(uncleared forest benveen each RO\S] (Figure 1-2). These include a relaux-el? complete. Il-year

record of soii and permafrost characteristics (moisture/ice contents. particle size. active layer

thchess) as weii as microclimatic characterisucs (Iiersha\v. unpublished data;. \'arious dismrbance

snidies have been carried out ar the site and they include work on the ecoIog~cal effects of a u d e oii

spills (Sebum 1993. Seburn et d 1996. Seburn and Kenhau- 199;). and permafrost depdauon as a

result of andiropogenic disrurbance (Gallinger 1990, G a h g e r and Kershaw 1988. Nolte 1990. Nolte

and Kershaw 1998).

In 1993. a u i l d f ~ e swepr over the SEEDS area burning orer 33 500 ha. This prorided an

ideal opporruni~ to assess the fie-e-liduced changes in microclimatic and permafrost condiuons. in

an area of d i s con~uous permafrost. These new objectk-es wdi be addressed in this thesis.

.---.--O..., Oi( pjp&m ------ Original winter road Ciearings Seisrnic lines and ------ Rtaiigned wintcr road Cam- in&it t2S ket abandoncd trails

Figure 1-1: Locaaon map of the S.E.E.D.S (S t~def o/ th Envzmnmenid EJ~C-IJ- qf Dzhurbanrrr M the Submtitj tesearch site (Kershaw 1991). The hamlet of Fort-Norman is now caiied Tulita ('Where the waters meet").

Figure 1-2: S.E.E. D.J. simulated transport corridor in 1 986- 1 !K. .Areas of I;'nA~tndcd /imt are now ce ferred to as b~~nredfimi. Kershaw (1 386).

6

GeoIogy and soils

The SEEDS site is siruared tvithin an area of flat. to gently sloping glacio-heusuine p h .

Local relief is g e n e d y by hurnrnocky miao-relief (Reid 1974. Zoltai and Tarnocai 1375). The

regional geolog- consists of Devonian dolomiac and limesrone breccias aith depths to bedrock of

over 5m (Hughes cf LI/. 1973, MacInnes c'l ut! 1989, Reid 1974). -1 thick (-10 m) accumulation of

deitaic sand and siIt u-ere deposired in die area bv the estensire Glacial Lake Mackenzie during the

iate KXlsconsinan (Smith 1990).

C n d the 1970's the soils of the hfackenzie valley remained undassified (Pettapiece 19'5).

Erans çt d (1988). Kershaw and Evans (1986) classified the pre-hre soils of the SEEDS site as

GIeysotic Turbic Cq-osols uith orgamc soil horizons 15-30 cm thick. These organic horizons sustain

a iayer of LI-e moss and lichen three to tire an thick. Soi1 pH was found to decrease with depth,

reflecüng the acidic nature of the peat. The soil testure \vas desaibed as sdty loam. nlth an average

clay Gacuon of 20' o and a Fie sand iracrion vainmg from 4' a to 55' O (Kershaw and E n n s 1986). -4

discontinuous coarse sand/ pebbie layer is present mithm the glaaoiacusuine sequence benx-een 132

and 333 cm below the surface.

Permafrost is widespread at the SEEDS site (Gn- rr d 1983, MacInnes P r 3r: 1989).

-4ccordmg to Broun (197C)j and N~xon et JI: (1983) the site taUs wirhin an area where approximateb

85' O of the terrain is underlail by discontinuous permafrost. Permafrost thchess does nor esceed

50 m (Judge 1973).

Climate:

ï h e c h a t r of SEEDS has been chssified as Subhurnid High B o r d (Ecoregions YCorhng

Group. 1989). The Tulita meteorological record shows that winters rend to be long with

temperatures reachng -30°C or less during fil-e months of the \-eu. The s u m e r s are short uith

only three months areragmg over lO0C (-icmospheric Environment Sen-ice 1982). ;innuai

preàpirauon is relatively low (mean annual precipitaaon is 460 mm). che majorin. of whch

accumulates in wkter as light snow-fails. Snowcorer is generally present from hte October to e a r -

May. However, 43'0 to 55' O of the total precipitation occurs betu-een June and September. when

rainstorms are frequent. The thaw season averages 95 to 123 da' and extends from May to

Seprember.

Vegetation:

Prior to the 1395 fke, a b o r d forest cornrnunity dominated by larch {L~Y ;rmLincl) and

bhdi spruce ( P i m mmclncl) approsimately 300 years old (Kershaw 1985, 1986j. The open-canopied

forest ranged in h q h t from +6 m. Tree morphologr- was characterized by single crown or s m d

groups of aees with crown col-er of approsïrnateIy 8' O (trees greater than 2 m in height) (Kenhau-

1988, Schotre 1988). The dorninanr shrub species were the Litde Cree d l o ~ v S ~ t f i ~ rlr611mi/oide~-.

s hnib b y &que foi1 (Porenrilf' jhr ico~z) and dwd birch (Bef~tii ~ h d r r i o ~ i l ) . Cnderston regeta tion

consisred rnainl~ of Labrador tea (Ldm gmenhndi~mn). bearberry d . l r i .~o~- tq~ . iu , - mbrï). bog cranberry

( I U~zinic~m x?rij-iherl) . bog blueberq- ( 1 jcsinium u~&ino~um) and crowberq- (Empetrrtm n&nim). Non-

rascular species provided. with exception of the uench, an airnost continuous cover on the ground

surface. Cornmon moss speaes included the feather moss (f-!~iorornni~inr ~pienden~j as we11 as

Tomenth_pn~inr niten,- and . I~tiLt~arnni~irn p i z ~ ~ ~ r e . Lichen species u-ere dominared b !- the genus Cihoniri

(Tiershaw L- 1988). The complete burnuig of the black spruce. the shnibby species. and p m of the understory

greatb- altered the regetation. LIost of the black spruce were M e d and onI!- bumed uees were lefr

standing. Tree cronn densiry u-as reduced to nil. The underscoq- \ras not cornpletel!- consumed

during the h e and regrou-th has been ongoing since 1993. In post-Fie conditions. there has been a

prolifenuon of the shrubbr speties (5. ~ r b ~ i ~ - d o i d t ~ - ) ! . The mean total regetauon cores in the posr-tke

control treaunent u-as 1 15' O. The dorninan t species were Ciudinu rni~i'~ (39" O coverj and PiLw mmmrl

( 1 8' O cet-erj. O ther dominant speàes inciuded 1 Aini i tm r i~ i . i - ih t . I : ~ ~ i ~ i n o ~ x r n . . - I T~.IoJ '~L&) '~oJ . mUm.

He~i.oiomnir<m pena>n~-. .krocarpous and pleurocarpous bqoph!-res accounted for 8* u and 0 corer

respectively Kers haw. unpublis hed data)

In the bumed treaunenrs. regetation \vas oniy present below 30 cm. Mean total corer in the

bumed forest \i?ls 3'0 uirh no speaes conrributing more than 1' O ro rota1 col-er. On the burned

ROW. mean total cover \.-as 18O0. This \vas dominated by non-vascular species such as .\lrlnhrlntirl

po[rrnotpba (8O.0 cover) and acrocarpous bryophytes (7' O corer). The prevalent rascuIar speaes was

Epiiobim u ? ~ ~ I J J I ~ / o / ~ z I ~ ( 1 O cover) (Kers hm-, unpu blis hed da ci).

In 1985 and 1987 mean cover in the undisturbed forest at the SEEDS sire was 148'0 and

1 U0 O respecavely. P. mununu cover was 18' O in 1985 and 17O O in 1987 (Kers han- 19883. The pos t-

h e control ueaunent had a uee stem density of 1.11 stems m.= (Kersha\v. unpublished data) which

was comparable to the pre-Ge stem densin of 1.06 srems m from the SEEDS ueaunents (Schorte

1988). Mean cover in the p s t - h e convol was less chan in the pre-Cire control. However. P. murimu

cover \ras comparable- mahng the post-Eue control an adequate andogue of pre-he conditions.

Structure of thesis and research objectives:

The rhesis has been subdivided into h e chapters. Chapters 1 and 3 are in t roduc to~ and

conduding chaptus respective1:- and Chapters 2, 3 and 4 deal uirh the microchatic changes

accompanying ddfire. rhe changes in soil characteristics and acrire layer depths and the

geomorphic response of a hre-affected permafrost terrain respectkel-.

Chapter 1 is an introduction to the rhesis srnicrue as well as an introduction ro the subiect marters

explored in chapters 2. 3 and 4. Ir contains a bnef Lireranue revieu- of permafrost research and of

the effects of disturbances on permafrost-affected terrains. Pa.rticular emphasis is placed on the

e f k s of uddfues in Subarctic regions. ;\ddiuonaliy. a g e n d oremieu. of the SEEDS research site

and proiecr has been oudined and the general sire amibutes of the research area are described-

Chapter 2 has been rided "Microclimatic responses to a Subarcuc upland forest following

wiIdfiren. The main objecaves of this chapter are:

i/ Perform a quahaci\-e cornparison of the post-fue microdimare condirions for four

surface ueatmenrs on the SEEDS sire (Right-of-\l'a!-. Trench. Burned forest and

Conuolj.

il) Quanu- the changes in the microchare factors rhat are determinant in the encrgy

balance of the surface.

iiz) Compare the values obrairied for these paramerers for each of the SEEDS creaments in

post-hre conditions.

Chapter 3 has been aded Soi1 propemes and thaw depths following Mldfire in a Subarctic

upland forest and on a simulated transport corridor". The obiectires ore:

il Quanti@ the post-fie changes in thau- depths and soii moisrure contents for the rarious

SEEDS treaunents.

ii) Compare the pre- \-S. posr-fie thaw depths and moisnire content for the SEEDS

ueatments.

Chapter 4 has been aded "Therinokarst subsidence and seasonal /long-terni terrain

modi6cations foiiowing fire and anthropogenic disturbance". Ir is cornplementq- to the MO

pretlous chapters and incorporates these data in a geomorphic ana l~ i s . The objectives are:

i ) Compare and quantifi- the t 997 seasonal surface change in each SEEDS treatrnent

ii) Determine the degree of tord surface subsidence r e s u l ~ g fiom burning and /'or clearrng

since the Liid dearing (1986) and the last topographie sure\- !1990).

Chap ter 5 UConclusionsn. conrains a bnef s u m m a q of the rhesis.

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Chaptet 2: Microclimatic tespouses to a Subarctic upland focest following Mldfire.

Introduction:

Changes in permafrost maïnly result Gom the modification of microclimatic conditions and

the heat exchange at the ground surface. Degradation or aggradation of permafrost as weU as

seasonal developmenr of the ac*e laver depend on these ground surface conditions Nouse 1982,

1983; YCiiIliams & Smith 1989). In mm. this energ?- eschange is greatiy affected br the narure of the

ground surface, and an- perrurbauons of surface conditions uill have direct repercussions on the

ground themiai regime @ r o m and Grave 1375; Brown and Péwé 19-3; \Sïlhms and Smith 1980).

XIdGes are one type of disturbance which cause changes in the ground thermal regune.

During the acmal bummg, litde modificaaon of permafrost conditions occurs (Brown 1983)- The

imrnediate effects of burning are negtigbie because the direct input of heat ro the soi1 ie s m d

because both mineral and organic layers are poor conducton. \*an \Yagner (19?0). found

temperature gradients of 10aC mm 1 in minerai soi1 and 28OC mm in p d y decayed organic

material. -4 remporaq- surface temperature of -CSO°C \r-ould cheretore have lirrle effect below 5 cm

depdi (Brown 1983). Post-he modidcauons of permafrost occur in the months and rears tollouing

burtlmg. as the surface energy balance 1s changed. The degree r o n-hich permafrost 1s moditled

largely depends on whether the tire burns only the uee cronns. o r rhe uees and the undergrowh to

the ground surface. or wherher the surface organic matter is parcially or completely destroyed

(Brown 1983)- Khere post-CTre regetauon recovers rapidly. the impacts on permafrost can be

rnitigared by the shacimg effecr of' nea- regerauon (Tsyrovich 19-5;. ;\ddiuonaiiy. the albedo w2U

increase as vegetauon recoveq progresses.

Objectives:

The objecuves of chis snid!. were ro:

t j Perform a qualitaave description of the post-Cïe microchate condiuons for four surface

ueaments on the SEEDS site (Right-of-Kay. Trench. Bumed forest and Conuol).

ii) Q u a n t i - and compare the changes in microclimare condiaons benveen burned treaunents and

control.

iii/ D e t e r m e the importance of the radiation budget components in modifjing the surface energy

eschanges in bumed and unburned surfaces.

Factors aecting permdiost and the ground thermal regime

In undisrurbed, pre-ike conditions, the t h e r d state of permafrost is in equilibrium uith the

prm-ahg microclLnate. In veas of d k c o n ~ u o u s permafrost. the "summer" penod (foUouing

snomeIt) is characterised by thawïng of the upper layer of the ground. This thawed rnaterd - the

actire i a y - atll x-ary in thïchess according to the amplitude of summer temperarures. ,\cri~-e laver

da-elopment is not restricted to areas of disconcïnuous permafrost. as it is aIso present in areas of

conrinuous permafrost but its thckness c m be much less.

The seasonai derelopment of the active iayer is detemillied b!- the temperarure regune at the

ground surface, the thermal propemes of the ground and the u=ater/ice content of the active laver.

.hmospheric mass and e n e q - flows and the geothennal heat tlus are b o u n w - condirions

accountïng for the equilibrium benveen perrna fros t and i ts surrounding environment, uith the

vegetation canopy. snowcot-er and the surface organic layer acting as buffers berneen the

atrnosphere and the mineral soi1 (Riseborough 1985).

- E$~LYJ- ot 're3e~~t ion on the rrlai'cttion brldgtt ~ n d t h gmmd thenncti' 23zmt:

ï h e imponance of regetauon in c o n u o h g the energ- eschanges of the ground can be

dk-ided into nvo caregories. according to wgetaùon architecture: the ot-erstory t-egetaaon iuee

canopy) and the bryophyte iayer at the ground surface.

In forested areas. the physical characteristics of the canopy are determinkg factors in the

energ eschanges benveen forest-aunosphere-pemafiost. Trees intercept a large portion of the dail-

solar radauon, thereby reducing the net solar tlus belon- the canopy Plunn t~ d 1978. Luthin and

Guynon 1971. Broun and Pe1.e 19-3. Haag and Bliss 1974 a). Some of the short-U-ave incoming

sadiation is reflected back to the aunosphere as a hnction of the aibedo of the uee crouns or laves

(Lafleur and =\dams 1986). .+nocher portion of this incoming radiation is absorbed by the canopy. -At

the same the . vees act as a source of long-wave radianon as the absorbed heat is re-radiated to the

aunosphere as weii as cou-ards the ground. Trees aiso affect air temperarures near the ground b!-

reducing wind tlow uithm and below the canopy (Haag and Bliss 1974 a). The impeded u-ind flou-

cannot dissipate sensible heat as readily as open areas and thus promores higher air temperatures

Seconda? roies also include the intercepuon of tarn and vanspiration by the canopy. This affects the

ground chermal regime by m o d i h g the thermal ~~~~~~~~~iry of the soil and the aibedo of the

organic laver as a hnction of the soil moiswe contents.

The surface organic iayer is often referred to as a buffer layer berween the near-surface soi1

e r i q exchanges and aunosphenc inputs of energ-. Three factors cited for this are: i, the lou-

conductit-i~ of organic soils re1am.e to minerai SOL N) the effecr of the seasonal variation in the

moisnue content of the ocganic soil on its conductiviry and, riz) the seasonal a-aporatil-e regune of

the surface, as controiied by dimatic factors (Luthin and Guymon 1974, Fitzgibbon 1981 [rom

Riseborough 1985). Because of these buffering charaaensucs, the organic (moss and lichens) laver

has been credited wïth rhe penistmce of permafrost in the southem margin of the d i scon~uous

permafrost zone. Nakano and Brown (1972) demonstrated the importance of thc properues of rhe

surface organic layer to the ground thermal regime using a computer mode1 of the thermal regune at

Barrou-. -Uaska. They conduded that die thickness and the moîsrure content a f f e c ~ g the latent heat

exchange of the organic layer eserred the greatest uitluence on the progression of the frost line

through the soil. -\ similar sirnulauon b?- Ng and 3filler (1973 indicated that the thermal conductiviry

of the surface layes Kas the most sensial-e parameter. while organic laver thickness was l e s

important dian some parameters (e-g. albedoj related to che energ- balance of the surface.

-E#eL-ts ot-~-f ioqrlL.k Liilma~-tmhiL~ on the g m n d rhennd nym:

Snow- has an irnporcanc influence on ground temperatures because of its insularing effect

that reduces uintes heac loss fi-icholson and Grandberg 1973). The effeca\-eness of the insulaaon is

proportional to the thickness of the snowpack as weii as its thermal conducci+. ahich varies with

snow densiry (Kershaw 1991). ShaiIotv snow accumulations otfer tirde insulauon, conuibuhg to the

maintenance and/or grotvth of permafrost @lacka?- 1995). ,\ddicionall!-. tree col-er has a direct effecr

on the depth and duraaon of the sno\\pack (Kershaw 1991. Rouse 1982. b d 198 1. Brown and

Pewe 1973). Dense regetaure col-er wiii create a barrier to winds chat scour and rediscribure snou-

accumulacions (Kers haw 193 1, Rouse 1982. 1983). -iddxionall!-. these barriers aill promote the

deposiuon of whd-mnsported snow. enhancing the insulation of the ground (IÜnd 1981). Howerer.

snow accumulauon under tree cover is mitigated by the retention et'têct of cree branches and shrubs

which can reduce the snow cover 011 the ground, thus Iowenng sod temperanues.

-Postjire eneg. exibunge~~ md cilJer-t~- on pemtfio~-t equiiibn'c~m::

I t is generally agreed that post-Eue permafrost esperience a deepening of the active layer as a

result of the disnipaon of the themal equtlibrium. The p d and/or complete rernoval of both the

overstoq- vegetauon and the surface organic la^ Iead to increases in the amount of energ-

p m e u a ~ g the ground and chus lead to acave iayer deepening. The removal of the trees by fire

eliminates th& role as interceptors of incoming radiation. This Ieads ro increases in the net solar Bus

at the surface as shon-wave radiation is no longer reflected by uee crowns and long-uxe radration

cannot be absorbed by the canopy. Eren if the surface organic cover is not completel!- removed by

tire, the biackenirig of the surface drama tically lowers surface albedo. This leads co an inuease in the

absorption of shorr-wave radiation resultbg in increased surface temperanires. Changes in the

albedo of burned surfaces hare been reported. but consistenq- of n.iues uithin a parncular corer

type are diff idt to obtali due to rariauons in surface moisnve contents at the t h e of obseri-auon

(Brown 1983). For this reason. spe~ific values of albedo are not andable. Nonetheless. there seems

to be an agreement that dbedos of burned surfaces van- bent-een 3-13"'. Early work by Jackson

(1959) and Davies (1963) reponed raiues of 9' O in areas of burned spruce-lichen woodland In

burned lichen-tundra. the posr-&e aibedo has been obsen-ed to r - becu-een -O O Peaold and

Rencz 1975. Rouse and ~~s 1976) and l5O O (Rouse and XUs 19'6). These posr-ltre values

consutute differences of 50' o 4 û O U o 01-er the albedos of similar unbumed surfaces Petzold and

Renn 1975. Rouse and Mis 1976, Oke 1987). Kersha\v tt d (1 975) reponed a rapid pos t - he drop

in albedo from 200 O to 3' O. chus giring a fresh burn the lowest albedo of any terrestrial surface.

Canopy remon1 and inaeases in albedo can lead to increases in soi1 and surface unperanires. Soi1

surface temperatures hare been reporred to increase by 60-X" O subsequenr ro canopy removal. Even

after 25 years. surface temperatures can rem& 30-40"0 warrner than tn unburned environments

(Kershaw and Rouse 1976).

;\nocher consequence of l o w e ~ g aibedo is an mcrense in ner radiation over freshly burned

surfaces (Kershaw tf d 1975. Haag and Biiss 1974 b). Hou-ever. conmdictory results hare been

reponed by Kershaa. and Rouse (1976) where burning led ro a reducuon in surnmertime net

radiation of 1 j 0 ~ - 1 9 0 ~ orer bumed surfaces of rarious ages (O, 1. 3. 24 and 81 !-r.). This &-as

aruibuted ro differenaal surface heating benveen sites of ditfërent ages. which increased the amounr

of outgoing long-wave radiation. These authors noted an inunediate decrease ui ner radiauon of ?O0 O

whch remained at kast 10° O lower than unbumed surfaces at'cer 3 0 Tears. They concludcd rhat the

low aibedo of freshly burned surfaces does not necessanly lead ro an increase in net radiation. Rouse

and h U s (1976) also found that net radiation deueased by 11' O orer burned areas as a result OF

greater long-wave Ioss offsetting the increased solar radiation absorption.

Fina*. uee removal affects the distribuaon and characrenstics of the snowpack. Open

burned areas d o u - for greater snow erosion by unchecked u-inds. This leads to thinner. denser

snowpacks thar favour frost penetration ro deeper depths than in undimbed areas. Consequendy.

snoupack thinning can lead to colder uinter tirne soil temperanires thar ma!- partiaIIy offset the

surnmertime deepening of the active la!-er.

Methods:

Mim~Ï'im(~te

hlicroclirnate stations and sensors were re-instded ui 1996 by Dr. Kershaw and rau; data

were esnacted Gom the data archn-e for anaiysis here. The initial installations were placed on site in

1985, 1 O vars prior to the 1995 uddfire-

Microchate data were coliecred at four locauons uithin and adjacent to the SEEDS site: 1)

burned forest, 2) bumed RO\Y. 3) burned uench and 4) conuol. -+il SEEDS treannents were

insvumented from 1986-1993 when a uildfue desuoyed most of the equipment. In 1996. neu-

stations were erected and data collection has been ongoing since. - I r each station, sensors monitored

soi1 and air temperatures. wind speeds. relative humidin-, preapitation and incoming solar radiation

throughour the v a r . .\ddiûonaiiy, "seasonal" sensors were instaiied during the s p h g and sumrner

months. In 1937. these were used to rneasure net radiation, soi1 moisnire and outgoing short-ware

radiation. Data were coiiected and stored on mtcrologgers.

Soil temperanues were measured using Ugauge. cpe-T (copper-constantan)

thennocouples. made accordmg to Johnston (1973) and attached to a 25 mm drameter wooden

dowel. Thermocouples were posiûoned at depths of 5 cm. 10 cm. 50 cm. 150 cm and 20(! cm. This

setup \vas used at the trench. RO\Y' and control stations. -Gr temperatures at +Si) cm and + 130 cm

were measured ~ i t h thermistors mstaiied in the relative humidity probes isee belou-).

Incomuig and outgoing short-wave (solarj radauon \vas mmsured with LI-COR !mode1

WUOS-L) pyanometers LnstaUed at a height of 150 cm on each srauon. Ourgomg short-wa1-e

radiarion sensors were incerted so chat the sensor head \vas oriented towards the ground surface.

Net radiation \vas measured wirh 2' (Radiation and E n e w Baiance Systems Inc.) net

radiometers. -4s \vas the case uith the rneasurernent of outgoing shon-wave radiation. esueme care

\tas taken to ensure that the surface belou- the sensors u-as not dtsmrbed during installation and data

coilecrion. -\ll the sensors measuring eneqg- tluses were insrded nichin or belou- the canop!-. No

instruments were deployed above the canopy heqht. Outgoing long-u-ave radauon uas calculated

from surface temperatures using equation (4). Finally, incorning long \rave radiation was obtained b!-

calcutating the residuai 1-alue from equations (1) and (2).

-At each stauon. mind speed was measured at nvo standard heights: 150 cm and MO c m using

XIET-OEYE anemometers uirh a programmed offset of 0.447 m *. ;\ddiuonallv, Cd@eif SLienrzbt-

(Mode1 2075 and \*aisala (lfodel HMP 35C) temperarure and relative hurnidtp- probes were

installed ac heghts of 50 cm and 1% cm. The data were recorded on a combination of C~"pbti/

SL-ientijG- automated dataloggers (lfodels CRlOS and 215 with attached memon modules). These

units were powered by 12 V batteries that were kept charged conünuousIy with solar paneis. Loggers

and power supplies were housed in protecuve sheltets.

Snow conne mcc~~~mnrentr.'

Snow sampiing was performed during the week of 17 Februq 1997. Sampling sites were

established in 1985 with pre-fke results reported in Kmhaw (1991). The sarne sites were used in

1997 since they were selected to protide representaut-e sampIes from each SEEDS treaunents

(Figure 2-1). Additiondy, 60 sites were randomly sampled in the control treaunenc. Leading edge

burned forest sites were witfiui the burned foresr, less than 15 m from the ROR' edge.

Figure 2-1: Snoupack sarnpllig sites on the simulated transport corridor. SEEDS, Tulita. hXT. Sampling sites have been categorized as bumed forest (sites 1, 2, 10, 11, 21, 22, 23 and 26). rranspon corridor (sites 3, 3, 5, 6, 7.8, 12,13, 16, 17, 18, 19.20 and 23) and leaduig edge of forest (sites 9, 14.15 and 25) (Kershau- 1991).

-At each site. 5 snow core samples u-ere exmcted uith an .\dirondacIï snou- corer. The sampling

technique used is outiîned b - -4dams and Barr (1974). -bd!-sis was based prima+ on the depdi and

densi- data derired from dus &ta set. The major site differences resultlig from erposure to wind

were noted During the ubirer. prmaillig wind direcrion was from the wesr-northwesr suiking the

chree 150-m long ROS's at an oblique angle (Figure 2- 1). ï h e MO 125-m long east-u-est comdor

segments were posiaoned ar approsirmrel- 30" to the p r a - a h g winter uind direction (Kenhaw

1991)-

Datu ana!pi:

The air temperanire data were analysed by using a "thaubig degree indes" flDI) and a

"freezing degree indes" (FDI). This rndes is the surn of all posiul-e P I ) and negatk-e (DI) air

temperanires during the measuremenr period The index s a s used as a means of comparing the

differences in cumulative air temperanires over each ueaunenr. Ir was also an indicator of the degree

of post-tire change in surface conditions that lead CO changes in air remperatures.

The microchare data were processed using the .\lïcrosoft Escel spreadsheer program.

Sranstical a n - s i s of the data was performed uirh the Jandel Sigrnastar soinvare package. Figures

and tables were produced b!- using a combination of Escel and Jandel SignaPlor soinvare packages.

Theory:

-Component~- q'rbr rddi~~iion 51tdget.

The radiation balance at the top of the canop!- or ar the ground surface can be espressed as:

where:

Q x is net (dw-awj radiation

I i L is Licorning shon-u-are radiation

a is albedo. the ratio of reflected to incoming solar radiauon

Lm is net Iong-wave radiation

L$ is incoming long-waw radiation

L? is outgoing long-wave radiation

The computation of this energy budget requires measurements of all energy fluses abot-e and belou-

the canopo. The instrumentation at the sites chd not aliow for the coUection of aU necessq-

measurements. The net long-u-ave component of equauon (3) had to be calculated. Outgoing long-

wat-e radiation uas derived from surface temperanites as follows (Oke 1989:

where:

E is ground surface emissirin

a is the Stefan-Boltzman constant (5.67E K m 2 O K 3

T is surface remperanue (Oh;

Since radiation budget caiculations began on Juhan Da! 156, mou- \vas not a factor in modifiing

surface emissivïry. The actual emissiriry of the surface \ras unknown but narurai surfaces c m

g e n e d y be assumed to have ernissi\-iaes close to unin Eagleston 1970). Because of the vaqing

thicliness of the organic laver and slight seasonal rnovement of sensors due to ground subsidence,

L? calcuiaüons for the RO\Y and burned forest sites were compured frorn tempemures integrated

orer the soiI surface and the f u s r h - e centuneters in the burned organic mat. In the conuol, this

\-due s a s integrared orer the soiI surface. Lichen mat and rree canopy mouse and Kersha~r 1971). LS \ras calculated as the residuai from equauon (3).

The solar tlus rctlected frorn the top of the black spruce canopy \ras not directl!- measured

but could be approslmared by the espression (Zaheur and -4dams 1986:):

where:

T 1s the coefficient of solar transmission through the canop!

Q;- is the ground surface aibedo

ot.1,: is the tree-crown albedo

In equauon (5). t was calculated as the ratio of incoming solar radiation above canop!- and incoming

solar ndiation below canop-. Because pyranometers were not deployed abore canopy, I;&

measured on ùie RO\X was assumed to be an adequate surrogate measurement of K& in the conuol

treatment. The close prosirni? of the w o sires (-1.5-2 km) and the fact that t;L (also L&) is

governed b>* large-scde atmospheric relationships d e s rhis assumption valid (Oke 1987. hfleur

and .\dams 1986). The values of ai< were nor measured in the hld . Values used for caicuiaoons

u-ere obralied from published l i r e n u e on rhe albedo of subarctic surfaces (Peaold and Rencz

1975: Pnce and Peaold 198-1: Wdson and Penold 1973). Equation (5j is ~ a h d insofar as solar

transmission through the canop- is assumed ro be isouopic (1-e. T is die same for solar radiacion

passing upuwd and dounward through the canopy) and multiple retlections of the rree crouns are

ignored. The open nature of die canopr \iith l jOo croun closure Kershau- L 1988) and the

generaily s m d albedo of the uee crowns indicate thar the errors associated uith rhe ptimary

assurnpaons are only a feu- percent (Latleur and -4dams 1986).

In order to inregrate the snou- deprh and densin values and to compare posr-Cm snoupack

modifications. a heat transfer coefficient (HTC, u-as used. Ir includes the influence of depth and

density in an attempt to assess the po t end for hem Ioss irom the rarious SEEDS ueaunenrs

(Kershau- 1991). HTC is d e h e d as:

HTC = C l d

where:

C is the thermal conductivi~- of the moupack

dis the snou;pack thickness (cm)

The thermal conducti\-in- of the snoupack \cls calculated irom the formula Kershaw 199 1):

where p is snowpack densin- (kg m ')

Results:

-- Iir temperat~m md degm inde-1- LÜiL~~/rl~ion~+:

During the period preceding the onset of chan* @ban days 50-1 15). mean daily air

temperature ar + I j O cm was lower han conrrol in the rrench treaunenr. The bumed foresr and

ROK' ueaunents were O.l?C. and 1.26'C warmer chan the conuol during the sarne period (Table 3-

1 ;\). Between Julian Days 116-162. the bumed forest and trench rreaunenrs were cooier than the

conuol. Differences raried from O.l°C to 226'C. During the same period temperarure on the ROK'

-0.24 -03 1 -0.76 -0.65 -0.-K) -0.'8 -0.43

no dara 1 . 3

-1.81 0.38

1-30 0.45 0-33 0.19 0.39 0.47 0.49

no data 5.30 1.93 3.75

- 1 .56 1.21 - 1.06 0.83 -0.08 0.45 7-34 0.68 1.24 1.01 1.1 1 2 15 0 . 7 0.9 1

no data no data 7.1 1 4-9 -0.84 1.58 0.98 3.49

136 4-13 0.46 1.82 -0.99 3.46 0.92 2-46 -0.97 4.13 0.50 4.49 -0.0 1 4.00 -1.14 6.83

no data no data 1.68 5.39 -1.41 1.90 0.78 3.74

1.1' 2-09 0.92 1.3 1 -O.7 1 2-54 1.47 2.52 1.37 4-40 1.65 4.03 1.18 3.66 -0.03 5.94

no data no data 1 .'3 4.80 -1.19 3.43 0.79 3.38

-035 4-10 -0.91 1.82 -326 330 -0.1 O 339 - 1.93 4.05 -0.63 4.37 -0.83 3--3 - 1.49 6.64

no data no dara 1.20 5-18

-303 1.82 0.12 3.69

2.58 1.1 1 0.55 2.6' 1 .BI 2.45 1.19 4.06 306 3-70 1.68 3 . 3 0.35 6.19

no data no data 333 4.39 -O.-l 1.36 1 .-50 3.28

Table 2-1: Mean & temperature diEferences and standard deviations between the control and burned neamiaits î r heights of A) 150 cm md B) 10 cm. Meîsurement periods indude the "uinrer" period be fore snowmelt (Julian Days 50- 1 1 5) and weekly segments for the rest of the measurement

period. The data period benueen Juüan Days 162-204 is missing due ro sensor maifuntaon. .Ui temperatures are in O C .

Figure 2-2: 1997 ak temperature rneasurements at standard haghts for -i) Control treatment, B) B m e d Forest treatmenr, C) Trench trearment and D) RO'X treaunenr.

fluctuated abore and below the mean concrol temperanves. The ROW exceeded the conuol

temperature on three occasions Vable 7-1 .A). The rnzximwn difference reached 0.910C (Julian Days .

130-1361. The ROK' was also cooler than the control on four occasions with a m u m

temperature difference of 0.9g°C @dian Days 113-139). Durkg the last 20 measurement days. all

burned treatments uiere w m e r than the control except for the period bernreen Julian Days 213-

218.

Mean dailv ai temperature at + 10 cm was much more variable than that rneasured at + 1 50

cm. During the ttinter period (presence of sïgnificant snowpack on the ground), up to the

commencement of thaw. temperatures tvere coldest on die ROW, foiiotved bv the burned forest and

uench ueatrnents. Khen cornpared tc the erench, mean dady temperatures were generally 3-F°C

cooler on the ROW and bumed forest treaunents. Temperanues in the control w-ere s d a r to the

SEEDS d u e s (Figure 3-3).

XIean d d y air temperature at 10 cm was more variable than at a height of 150 cm. The

burned forest elchibited the most variation as standard deviation values were -KI0 O-50'0 greater chan

l50cm values. During the tvinter period, the mnch was die warrnest burned mearment followed bu

the burned forest and ROW. Follotçing thaw and for the remainder of the surnmer period the

crench remained warrner than the control (wirh the exception of one week benveen Julian Days 212-

21 8) (Table 2- 1 B) [Figure 3-3).

The highest Thuwiing Degree Inds P I ) was recorded in the burned forest. foliotved by the

control and R O K treatments. The trench had the lowesr TDI. consatuthg a clifference of Y o from

the burned forest. The F ~ e ~ n g Agne 1nde-x (FD I) \vas greatest in the trench and decreased in the

c0ntr01 . ROW and burned forest treaunents respecavely. The trench FDI was 1 l0 o greater chan the

burned forest. The difference in thawing-freezing degree indeses (A) indicared a 52'0 greater

number of freezing degree days for the trench Fable 2-1).

Freezing 1 . -- -

Table 2-2: 199' degree indes cdculaaons for the SEEDS and control treatments. The data period used for calculations is frorn Jdmn Days 5 1 - 16 1 (FDQ and 204-22- (TDI).

-Rzhtire h11midi9.

The pattern of relative humidi- disrribucion was si.& in ail four œeaunent ppes. The

p ~ c i p a l difference \vas the greater amplitude of the relative hurnidicy in die conuol when compared

to the other ueatments. Peaks in reiauve humidity in the control u-ere 23-23"' p a r e r than for die

SEEDS ueatments. S1Liimurn values only differed by 3-5' O benveen burned and unburned

uetrtments (Frgure 2-31.

- IC'ïnd p e d

The connol treament had lower mean dail! ~ u i d speed than the bumed treamenrs. The

average for the whole measuring period indicares wind speeds that were 0.63-0.66 ms and 0.68-0.71

ms.' 10%-er at +300 cm and c l50 cm respecrively in the control stand. -4mong the burned

treaments. uind speeds were slighdy hgher in the bumed forest rhan on the ROK' (0.03 m s - [ at

+300 cm and + 1 SO cm)(Frgure 2-41.

-hdicltion b11d3~'r

Incomin~ short-\va\-e:

Levels of incoming shorr-\va\-e radiation were s d a r on burned foresr and RO\X surfaces

(Figure 2-5 .i). The difierence \vas less rhan T u . In the conuol. radiation levels were 50-200 \Km:

lotver than the bunied treaments. llinunum radiation let-els were uithin 2" O at ail treaunents and the

greatesr difierences occurred during peaks of masimum radiauon [Figure 2-3 .ij.

O u t ~ o i n ~ - - s horr-\vave:

The parrern of ourgolig radiation was s d a r in all ueamienrs. ROU- and burned foresr

eshibited slnilar levels of outgoing ndiaaon diroughout the measusement period (Figure 2-5 8).

During peaks. the control ueatmenr eshibited lerels thar were 20-30 R'm = lower than the bumed

ueaunents. .iddiaonaily. during periods of radiation minima. lerels were equal at all bumed sires.

Radiaaon lerels ar the bumed uearments were 3-5 \ K i n higher rhan the control (Figure 3-5 B}.

Julian Day

Figure 2-3: 1997 relative humidity measured at 150 un in .A) Bumed Forest matment, 8) ROW aeaanent, C) Trench treatment and D) Conad.

Figure 2-4: 1997 mean daily vind speed masured a< nïo standard haghrs in .\) Row neaûnent, B) Burned Forest neaunent and C ) Conuol rreamient. Wrmd speeds indude a programmed offset of 0.-U7 m/s. Line breaks are due to data @p.

Figure 2-5: 1397 mean dady shon-wat-e mergy tlux components for the ROW, Bumed Forest and Control treaunents; -i) Incoming short-wave radiaaon, B) Outgoing short-wave radiation, C) -Ubedo (caic&ted). Line breaks are due to data gap.

Albedo:

-Ubedo was hqghest in the conuol ueatrnenr. L-dues flucruated beween 7' O and -11' O. In the

burned ueaments. albedo raiues varied bem-een 20 O and 18" O. During periods of minima, aibedo

values were sirnilar in both burned ueaments. Peaks in aibedo were higher on the R O K for the

perïod beween Julian Days 303-208. This situaaon u-as ra-ersed bent-een Julian Da!-s 217-119 when

the Burned Forest aibedo was hrgher than the ROW ( F i e 2-3 C).

Incomin~ Ionp-u-al-e: - Incorning radiarion was htghesr in the control ueatrnent. During periods of concurrent data,

peah in long-uâve radiauon in the control w-ere 50-300 \X m-2 greater than the burned ueaunents

(Figure 3-6 -A).

Out~oing Ionp-wal-e:

Outgoing long-wave radiauon was highest in the b m e d forest alrhough the conuol had

\-dues that were genenily within 10 \Y m.'. In conmst. the ROW values were 33-50 \K' m' lower.

Peaks and iluctuaüons were synchronous in the burnea forest and conuoi ueaunents but rh is u a s

not the case in the RO\Y' treaunent. This dmribuuon was more constant with an absolute seasonal

amplitude of 30 K- m 2 in cornparison to the -90 \Y rn: amplitude in the orher nvo treatrnents

(Figure 2-6 B).

Net ahc-ave radiation:

Net radiauon \vas h h e s t in the w o burned ueaments where die discribuuons were

idenacal throughout che measunng period. The pattern of radiaaon in the concrol resembled the

other wo disuiburions. the principal difference being lower radiauon lm-els in the conuol. Peaks of

net radiation in the bumed ueaunents frequendy reached 180-IN) \.' m = while correspondmg peaks

in the control attained 140-1 SC, K' m = (Figure 3-6 Cj.

- Rrldi~ttion 6114e1 " o n p ~ n i o n . ~ be~ween brrmed und m t m / treutrneent~:.

Short-wave radiation and aibedo:

Incoming short-wm-e radiation in the conuol ueaunent was 11-50'0 lower than in both

burned ueaunenrs. Outgoing short-wave radiation in the

conuol bv 1+30°~. Ground surface albedo v a s greatest

generally 35-67'' O lower in the burned ueaunents (Table 3-3.

b m e d treaments was lower than the

in the concrol ueaunent. 1-dues were

Figure 2-9.

Figure 2-6: 1997 long-wave and net enew flux cornponenrs for the ROSI Bumed Forest and Conml aeaunents; -A) Calculared incoming long-wave r;iciiauon, 8) Modeiied outgomg Iong- wave radiation, C) Sec radiation. Lrne breaks are due to data gap.

Low-wave radiaaon:

Incornmg long-wave radiation was greater in the conuol than in both burned treaunents.

Differences v d e d between 133°,~. Outgoing long-wave radiation was generaily greater in the burned

forest. closel>- foUowed by the control meatmeut. Kkh the exception of the period between Julian

days 210-216, the ROW treament e-xhibited the lowesc levels of emitced long-wave radiaaon Fable

2-3, F i e 2-7).

Table 2-3: Weekly averages of radiation budget components for the Burned Forest, ROW and Controi treaments during the 199' masurement period. .Ill radiation filues are in Km '.

Net radiation:

The cornpurauon of the net radiation budget revealed the highest net radiauon levels in both

burned trearmenrs. Net radiation \vas generally 5-33Oo lower in the control. .irnong the burned

treaunents, rhe burned forest e-shibired radiation levets thar were 0.8-2.1' O higher than the ROW

t r amen t (Table 2-3. Figure 2-7).

-Soir' t e n p r i z f z ~ m

M a n monthly calculations of sod temperatures were obtained [rom the m a n dail!-

temperarure data. During "ubitu" months (January. Febmui; March and -4pnI). the uench u u

the warmest of aii uemnents with surface tempetanires of --?OC. Throughout this period the

control creamenr remained the coldest with surface temperatures of -6 to -Soc. ROUF and Trench

sites had sKnrlar temperature profües during the four aimer months. The gmund surface

temperature raried beween -6 and -8 OC (lanu-. Feb ru - . Slarch) and -'OC (.\pnl). .U

rempenture am-es conx-erged at a depth of -150 c m where mean temperature wa belou- O°C

(Figure 2-81.

During spring and surnmer months (May June. !ul!-. .iugust). surface remperuures became

posiave. The conuol rreaunent u-as one of the coolest trerrments at all depths duMg &fa. and June.

This changed in Jdy-.+pst when the uench was rhe coldest trament. In Ma!- 2nd June. ail

rreatments analied a temperature of O OC ar a minimum depth of 50 cm (Figure 2-7). In July and

.iugust. uench and conuol temperatures remained below freezing at 90 cm depth &sr bumed

Fomr and RO\Y rreatments only reached O°C ar a depth of 150 cm. Surface temperames gradually

lncreased d u h g the "summer" period. r q w g from 4-4.3Y (Ma-; to 1--lS°C (.iugun) (Figure 2-

8).

Snow~ack de~th :

In February 1997. mean snou-pack depth in the conuol ueatrnent \vas 54-28 cm ( ~ 6 0 .

S.D.=3.62). For the same period. mean dep th &-as only 3' 0 ( 1.3- cm) greater in the h e d forest

than in the conuol. Snowpack depth \vas more variable in the bumed forest as standard deviarion

values were greater by 5.94 cm (Table 2-4 -4. Figure 3-9 -\).

.Uong the oorth-south oriented ROK. snowpacks were deeper on the western edge and

slow-1:- thïnned ro\vards the easrern edge where depth \vas 9.51 an shaliou-er. Yariabilin. in

snowdepth was also grearest on the west edge as ir also decreased uith an easward trend .Uong the

easr-west orienred RO\Y. mou- depth uas grearest in the uench. closely foilowed by rhe easrern

edge. RO\Y center uas -il0 O shallower than the uench. Snow d n f ~ g uas noted on site as evidenced

by the development of smaii snow ridges on the leeside of burned standing snags.

Figure 2-8: 1997 mean monthly soi1 temperature profiles for the bur SEEDS ueatrnenn

38

The leading edge sites e-shibited the greatest o v e d snowpack depth of ail S W S ueaunents.

including the control ueamienr Fable 2 4 -\). hlean snow depdi aas 3-72 cm greater chan conuol

with onlv a 0.32 cm difference in standard deviation.

Snowack densin?

Khen compared to the control snowpack densin- was greater in aii burned forest

aeamimts. .Uong the ROW. the trench. the easrern edge of the no&-south orienred ROB* and the

cenrer and eastern edge of the easr-wsr orienred R O K densities were lower than in die conml.

In the burned forest the a-esremrnost section eshibired the highesr densi?. E s u-as

followed b - the eastern leading edge sires. The difference benveen t h a e sires raried benveen 8.1 and

29.3 kg m-' (Table 2-3 B. Figure 1-9 -4).

;Uong the nonh-south orienred ROE'. snow- densin- decreased h m the western to the

easrern edge (2113 kg m.' to 149.1 kg m 3. 0- die western edge and the RO\Y center had densin-

ralues greater than die undisnubed foresr. ïhe geatesr o r e rd snow density w a s obsen-ed ar the

western edge sires. The uench sires had the lowest snow densiry of ail sites (1 45.- kg m').

The easr-w-est oriented RO\Y had snoupack densiues tliat u-ere generall!. Iower chan the conuol by

2-57 kg m m ; . The ody cscepaon u l i s rhe uench with density ralues 11.3 kg m ' greater than the

controI (Table 2-3 B. Figure 2-9 -4,-

Leading edge sires had mean snolipack densities thar were 6.1-19.2 kg m ' greater than

d u e s from undismrbed treaunenrs.

Diffimies h ~xozaptack dqpth ma' demifi. brtween hrned und mrtml trerltmrnrj-:

Posr-Ge snoupack depths of disturbed sites were grearer than conuol at only diree sites:

BnY. BRK. BFEE (Figure 1-10 .il. However, these differences were sùghr. averaging 1.5 - 4 cm. .Ar

all other mes. snowpacks a-ere t h n e r than the conuol treatmenr. Both cranspon comdors

eshibired snowpack thinning. The grearesr difference was noted in the center portion of the east-

West orienred RO\Y where the snou-pack uTas -23 cm thinner than die control and -26.5 cm chuiner

chan the burned forest.

Sites with greater-han-conuol snowpacks dso had grearer densities. The differences ranged

from -6-59 kg m.'. .\ddiaonaii- three sires nith lower-rhan-control snowpacks had grearer densities:

BRC. BFE. BET. Differences only ranged from + 12 kg m ' (Figure 2- 10 ;\).

B F W BRW BRC BICT BRE BFE BRCE BET BREE BFEE

m - - 115

FW R E RC i;r RE FE RCE REE FEE

Loaaon

Figure 2-9: Cornparison of mean -3) post-tire, Febmary 1997 snowpack depth and densi- and 8) pre-lire, Februacy 2986-2989 snowpacb: depth and density (Kershaw 1992) on a simulated transport corridor, Kev to locations: (B)FW - @urne4 focest upwind of rights-of- way (ROW); (B)RW - (burned) West edge of no&-south-otiented R O W (E3)RC - (bumeci) center position on no&-south-oriented ROW, @)NT - (burned) north-south-oriented simulated pipeline mnch; @)RE - (bumed) east edge of no&-south-oriented ROLR @)FE - (burned) leading edge of focest on east side of no&-south-orienred ROU' or south side of est-west-orieated ROLq (B)RCE - (burned) center portion ofeast-west oriented ROW (B)ET - (bumed) est-west-oriented pipeline trench; (8)REE - (burned) east edge ofeast-west- oriented ROVe'; (B)FEE - (bumeci) leading edge of forest on east side ofeast-west-oriented ROW.

I 1 I I I i 1 I 1 1

BFn;' BRIX' BRC BNT BRE BFE BRCE BET BREX BFEE

-30 f 1 1 1 1 I 1 1 1 1 1

F'K RTX' RC XT RE FEl RCE ET E F E

Location

Figure 2-10: Diffuences in deph and density between snowpacks on, or affected by a simuiared transport comdor and an undistubecl brest in A) port-File condiüoas (Febniaxy 1777 and B) pre-frre conditions (Febmary 1786- 1989). See caption Figure 2-9 for explanauon of location.

HCUI fmnrfer ~ a + ? f i & H t HTC):

ROK:

The low-est HTC d u e s were recorded ar sites dong the transport corridor. --\il ROW HTC

d u e s were bdow 0.165 \Y m = O1.; l . the lowest being 0.135 \X m.: O K 1 at the eastern edge of the

east-west oriented RO\S'. The oniy exceptions were che cenve portion of the east-w-est oriented

ROW and the western edge of the nonh-south oriented ROK' whch eshbited the hrghest HTC

d u e s (0.3 \X m = OE; and 0.25 W m = OIi respectively)(Figure 2- 1 1 -\).

Bumed forest and Ieadine e&e sites:

-U burned fores t sites had HTC values above 0.136 \Xe m = O K '. Kithm the burned forest,

the highert HTC u-as recorded at leading edge sites where ralues O i 0.2 \Y m = OI; were attained.

The second leadhg edge site had the lowest HTC of ail bumed forest sites (O. 156 \Y m O K l).

However. this was htgher than al1 but one of the RO\Y sites (BE) where there u-as a difference of

onlv 0.08 \S' m = 'II; ' (Figure 2- 1 1 -4).

Pre-Lie HTC ralues were greater at all locations sare for die leadmg edge sites on the east

side of the east-wesr oriented RO\X (BFEEj, the bumed iorest site (i3FW;. and the u-est edge of the

no&-south oriented RO\Y (BR\\). The greatest differences occurred ar the ROW sites u-here pre-

fue HTC uas at Ieast 0.06 \\- m = OK greater. The east-wesr oriented RO\T' sites differed the mosr

from pre-fie values. This w s panicularly srriklig at the RO\Y centre site. rhe uench site and the

east edge site where differences reached -ci. 18. 0.083 and 0.08 \Y m = O Ç ; ' respectirely (Figure 2- 11

Comparing HTC ralues of dsnirbed sires wirh their respecure control trearments is the

most reiiable rnethod to assess the changes in snowpack conditions foilo\sing fie. This cornparison

eliminates the effects of seasonaliry of the sno~ipack. In post-tire conditions. control-correcred HTC

values were grearer than pre-tire ralues at Ieading edge sites (BFE and BFEE). on the u-est edge

(BRLX') and in the centre of rhe nosth-south oriented RO\Y (BRC). The greatest difference occurred

ar the BRIX sire where post-tire HTC difference was 600° a p a t e r than in pre-Lire condiaons (Figure

2-1 1 B). -At al1 other sites. post-rire control-corrected differences were equal ro or lower than pre-tire

conditions. The greatest differences occurred on the c e n d porrions of the east-\est oriented ROW

(sites BRE. BRCE and BET) (Figure 3-1 2 B).

Figure 2-11: A) Cornparison of bem fruq4pt roefl&nt (HTQ values between snoapacks on, or affected by, a simulated transport comdor during pce-fire conditions (1986- 1989) (Kershaw 1991) and port-Eire conditions (1997). B) Differences in HTC values between snowpricks on, or affected bv, a simulated transport comdor and an widisnirbed forest durhg pre-6re conditions (1 986-1983) (Eüxshaw 1991) and port-6re conditions (1997).

Discussion:

Rad'ration brrdget ~ v n p t u o n r between bumd and iontml tnatmenrr

Short-wave radiation and albedo:

The lower Imels of uicoming short-wave radiation in the conuol treaunent resulted Erom

the presence of uees which partially bloclied incoming radiation. The measured radiation l e d s ae r e

lower than results reported b!- Haag and BLiss (1974 b). Th- noted chat approldmatel- 80° O of total

incorning radiation penetrared to a height of 2 rn, the remainder beïng scattered or absorbed and re-

radkted by d e r vegeratïon- In the controI treatment 40-79' O of total incoming radiation reached the

sensor head at 150 cm h q h r . These lower levels ma? be due to differences in prevailing weather

conditions and the percentage coverage of regeration at the SEEDS conuol maunent (47.8' O)

(Chapter 1) which was 7.8' o greater chan the col-erage reported by Haag and BLiss (1974 a).

Lm-er les-els of outguing short-am-e radiation in the burned ueaunent were not une-xpected

considering the abrupt surface datkening after die h e . The albedo values for che burned ueaunents

were consistent uith moçt of the published literature (Rouse and Slills 1976, Kershau- et UL 1975,

Haag and BLiss 1974 b).

From the weeklt- arerages of the radiation componenrs. it \vas apparent that short-wave

radiauon and albedo were the conuoiiing factors on the changes ui surface tempennires and. thus.

the rnodilicauon of permafrost. In al1 ueatments. La (net long-wave radiation) values u-ere always

negative as a result of greater fluxes of outgoing long-wave radiation. In cornparison. the htgher K'

(net short-wave radiauon) values in the burned tratments led to tncreases in surface temperatures.

Surface blackenuig and the lowered albedo irnpamd the grearest control over the partiuoning of

incornkg radiaaon ar the surface. Tree remord d so conmbuted to the dominance of the shorr-w-a\-e

radiation componenr by allouing greater amounts of radiation to reach the surface-

LO~P-wave radiation:

The bumed forest site eshibired the grearest amount of ourgoing long-ware radiauon. This

was not unespected since fluses of outgoing long-wave radiation 1-aq- only lki th surface temperames

(Kershaw et d 1973, Oke 1987). =\t chts site. the post-fire albedo deaeased. causing greater

absorption of solar energ'. hgh surface temperatures and hence high anission of long-wax

radiaaon (Rouse and S U S 1976). Ir w s surpriskg chat the ROU' treamenr had the lowesr I e d s of

outgoing long-aave radiation despite recking levels of incoming short-wal-e radiaaon that were

sirnilar to the burned forest ueaunent. These results mal- reflecr the posiuon of the meteorologicat

staaon and rhe topographie characteristics of the ROK' itself. Throughout the SEEDS site. the

ROW generdy consututes a depression where rain and rnelm-ater tended to drain. The uench.

ROW and adlacent areas were often waterlogged. This high moisnire content may have reduced

suthce ternperatures, and hence outgohg long-wxe radiation. through increased rares of

evaporative cooling of the surface (Oke 1987). This uas supporred by a m d of increasing long-

wave emission during the lacer part of the measuring period as the surface dned and ernisskïry ma!-

have increased ( F i e 1-6 C. Table 2-1). More Wiely. higher uuid speeds on the R O K would

dissipate sensible heat more effiaently through greater rates of advection (Haag and BLss 1974 a).

Higher leveis of incoming long-mm-e radiation were recorded in the conuol as a result of the

tree canopr t e - r ad i a~g absorbed energy (Haag and BLiss 1974 a, Lafleur and -\dams 1986).

-\dditionally, the relatively high IereIs of outgoing long-ware radiaaon ma!- have resulted from higher

air and surface temperatures as a result of reduced advemion (Haag and Bliss 1974 a) and utcreased

uapping of e n q - by the uee canopy. The high absorptirky of evergreen uees rnakes hem

extremely important in the radiation budget of high latitude landscapes (Oke 1987. Lafleur and

;\dams 1986). Th& importance is accented at lou- soiar altitudes as the trees present th& ma-simum

surface area for kadiauon, and their receking surfaces are h o s t normal co the solar beam. Their

relative warmth rnakes h e m sources of long-wave radiation which is readily absorbed b!-

surroundhg surfaces (Oke 1983.

Net radiation:

Net radiaaon \vas appreciab1: greater in both burned ueatmenrs chan in the conuol. 17us

was in agreement wth Haag and Bliss (1974 a. b) who attributed ths increase to the rapid change in

surface albedo and a nse in short-u-ave absorption orer the burned surfaces. ,-\dditiondy. the

transpiring plant canopy in the conuoi u-as able ro draw sub-surface moisrure through its roots and

continue to dissipate a large porrion of net radiation as latent heat (Haag and BLiss 1974). Howe\-er.

these findulgs are contradicted by Kershau- et ul. (1975) and Rouse and Mils (1976). Eiershaw- tt cl/:

(1 975) reponed a reducuon in surnrnertime net radiation lascing up to 8 1 years.

Most soi1 ternperatures when the soi1 is frozen. pnor ro snotrmelt. do nor differ significandy

arnong die different surfaces. so thar the lugh air temperatures w-hich are achieved in early surnmer in

the burned treatments must be accompanied b!- a large increase in soil temperatures (G).

-+dditionaily, the rates of evaporauon decreased substantially after the trrçt year of buming due to

Iower soi1 moisnire Iargely resulting €rom the ml!- melting of the snowcorer orer the bumed

surfaces. and the lack of cranspiring regetauon, which could have tapped moisrure from the deeper

soil layers. Because the decrease in evaporation which accompanies buniing is greater than the

decrease in nec radiation. the sensible heat Bus ot-er burned surfaces is greater chan oves unburned

surfaces.

In the case of the SEEDS fire this siruauon ma? not be direce applicable as a resdt of the

ciifference in the intensiry of the fie. Haag and Bliss (1974 b) have suggested several factors which

ma? esplain a deaease in post-fke ts-aponanspiration despite hgher d u e s of net radiation. These

kduded increased resistance due to surface m g , a muichmg effect frorn ash and iicter and the

removal of the cranspiring plants. -4ithough evapotranspiraaon \vas not measured at the SEEDS site.

it is possible that these rhree factors accounted for the htgher levels of net radiation ocer the burned

surfaces. -%O, dependmg on the intensin- of the fire affecnng the site srudied by Kershaw ~ . t JI:

(1975), the liner could have been completek consurned etimuiating the mulching effect of the

ash/lirter mis and increasing sod surface temperanires. Finaüy. die lowered evaporation rates one

year after burning uill depend iargely on the moîsture and ice content of the active-laver. Surface

dr+g will occur at differenr rates as a hnction of surface moisrure and evaporarion udi be

prolonged over wetter surfaces. It is possible that the h g h moisrure content of the SEEDS active

laver d o m evaporauon to occur weU beyond the fm t post-fke year.

-.!i'noqtm& dqtb

ConuoI ueaunent:

During pre-tire condiaons. the sections of undisnirbed focesr benveen each ROK' were used

to compare snowpack depths ~11th d u e s from the uansport corridors (Kershaw 1991 j. In 1997. this

area usas not used as a conuol ueaunent as it had burned and the surface condirions were

hndamenrally altered. The post-Cie control ueaunent u-here microchate stations u-ere erected was

dso used as a control ueaunent during snow samphg. The lack of data conceming total seasonal

snou- accumuiation at the SEEDS site in both pre- and posr-fire conditions resuicts direct

comparkons of snowpack characterisacs. -4ddiuonaU!-. using snow on the ground data from the

Norman WeUs meteorologicd station as a cornmon conuol to each site u-as nor possible since the

location of the station grossly underestimates snowpack depth O;crsha\v f 99 1).

Burned Forest:

The grearer-than-control snoupack deprhs and densiaes in the bumed forest resulted €rom

the redistribution of snou- trom unchecked winds. Inaeased snow density in wind-scoured sites has

been reported by Rouse (1982). The removal of vegetaaon b!- Lire decreased surface roughness in the

burned forest fadtating snou- drifting and increasing snou-pack density.

North-south oriented ROW:

*Uong the north-south onented ROW. the decrease in snowpack depth easmard was a

direct consequence of increased erosion of snow on the simufated transport comdor. .iIthough the

removal of vegetation in the bumed forest substantially deaeased surface roughness. the standing

snags still affect the boundq- layer to a greater degree than on the simulated transport corridor. This

effect w-as enhanced in the u.uzter as most t o p o p p h c irregularities were infded by snou- and erect

shrubs were incorporated in the snowpack (Kershaw 1991). \-egetation remord has increased the

distance of fetch fer prei-admg winds. thereb- increasing the degree of snow deilauon a-- from the

edge of the ROW: For esample. the western edge of the no&-south oriented ROW' had a mean

snowpack depth 5.36 cm Iess chan the adjacent burned forest. 'fhis difference increased to 15-85 cm

on the as tem edge as fetch dong the ROW was greatest at this point. This effect u-as panicuIarl!-

pronounced at these sites as sampling locations were oriented approsirnately parallel t a the prevailing

wind direction.

Eas t-wst oriented Roi\-:

Kershaw ( 199 1) reported that snow drifts accumdated on the leading edge of the forest on

the dounwind side of the ROK-S. This resulted from deflaaon of the snoupack on the veeless

RO\Xs. Lmding edge snoqacks were consequendy enhanced by 23.9O 11 and 3.4' t, over the control

on the east-west oriented ROiY and norrh-souch oriented ROWs respecuvely. niis conmsted

strongly uith the post-fie leadmg edge snow characterisucs. The leading edge of the nonh-south

oriented R O W had snou-pack depths that were 30'0 less than the control treaunent. Concurrendy.

the east-west oriented ROK- eshibited only a 6" O increase over the conuol. -{gain. ths increase &el!-

resulted from the rernoval of regetauon between the R O W s and the estended ktch distance. During

pre-tire condiuons. the uee canopy and lotv-lying branches slowed ~ i n d from the RO\Ys and forced

the deposition of cransported snow. In post-fire conditions. uee remord would permit t'aster uind

speeds and increased snow enmainment on the ROK's and doumnind RO\Y edges. This clearly

suggests that the remord ofvegetauon and the associated Fetch increase has transforrned the foresr

edges from areas of snow deposiaon to areas of net erosion.

Convoi treaunen t

Mid-uinter snonpack densin in the control meaunent was Ion-, but npicd of snoupacks in

the Subarcac (McE;ay and Findlay 197 2 . Pruitr 1984). .\ddiüonally. densi- vdues u-ere nor markedh-

different than during pre-ke conditions (see Kershaw 1991). These s d a r i a e s resulted from the

open-canopied cree cover that provided surface roughness and reduced snow movement and drifnng

(Jeffrey 19711. IUnd 198 1). These conditions permitted @ii (Pruitt 1958) budd-up and snou-packs

rhat were nor orerly densitïed by wind.

T r a n s ~ o n comdor

\'Cith the esception of w o sites (BR\+' and BRC) on the north-south-oriented ROK' densin

was Iower than that obsen-ed in the conuol during post-tire conditions. f i s \.-as a remarkable

change from pre-fie conditions uhere di sires. 'YL-P~ RU* and RC. exhibited greater snow density

than the control 6 e n h a w 1991). The greatest change occurred on the western edge of the norch-

south-oriented RO\\;'. where densic- increased aimost 60 fold. Thrs change \vas agam atuibuted to

the increased xlind effects on the snowpack. The open nature of the ROK-s fax-ored higher uind

ve10aties ar the ground l e d . resulting in increased rares of snow- removal. -4dditionall~. the RO\Ys

were areas of snow deposiuon during periods of decreasing wind velociues. This snow \vas alreadl-

mechanically metamorphosed (oblitention of crysial arms through saIrauon. etc-j and packed with

greater densin than freshly-fallen snow. This resulted in snoupacks eshibithg decreasing depths and

densiaes across the north-south-onented RO\S'. This situation was rex-ersed dong the east-west-

orienred ROW. where sno\v depth and densi? increase easnvard. Tu-O sites along dus RO\Y' B R C E

and BREEj had densi? values chat u-ere lower than control u-hile tu-O other sites had depth and

densiry values greater chan the control. The Iower posr-l?re densiry values can agam be atuibuted ro

high rares of snow erosion and metamorphism. Both sires had snow densiry values s d a r ro the

control d u e s (Table 3-1) !-et mou- depths were 8" O and 45' O shaiiower than conuol. This \vas a

prime esample of the densificauon process assoaated with snou- dnfting. I r \vas parucularly well

esempiified by site BRCE (site 3. Figure 2-11 located on the norrhem edge of the ROW. had

ma-sirnized fetch distance for the w-inds affeccing it. For sites BET and BFEE. the h.gh snowpack

densic values resulted from the lengrh of the ROK' and its Ion- surface roughness. In the case of sire

BFEE. RO\S' length u-as again a significant factor in determinhg the densin of the leadmg edge

snoupxlr since it was the distance over u-hich die snow couid be entrained and u-ind-eroded upuind

of the sarnpiing site. Prekrential redeposiâon occurred in the tirsr 3-4 m of the forest as tree snags

created enough surface roughness to perturb wind flow and alIo\\- deposition. The redeposited drift

snow had a higher density due to che modification of grain sizes duruig transport as weii as wînd-

paclruig effects (31cKay and Gray 1981).

Heat Tmn& Coefl~ient und J-oz/ temperuttim-:

-Uong the transport corridor. the high HTC talues resulted from h h snow density. Despice

having considerable snou* depths. Compared uith other sites. these areas would be pooriy insulared.

resulting in grearer winter heat loss than adjacent aras. This should also result rn colder near-surface

soii temperanires and perhaps enhance frost penetration. Xe=-surface soil ternperawes were indeed

colder in die burned forest and R O K u ~ u n m t s . The 10x1- HTC d u e s along the crench were

suggestk-e of low-er rares of heat loss occurring at these sites. This is in agreement mich the soil

temperature data with the trench +bac u-armer that the ROK and burned forest trearments.

PR- UJ. po~tyire ionprln'~-o n~. -' H TC r ~ I ~ Z J J :

1997 sites u-ith the greatest HTC differences trorn the conuol also had the Lou-est difference

tfom the 1986-1989 data. This \vas similar to densiry in post-hue condiaons \\+here there \ras a

reversai of pre-Cie conditions. From equauons (6 and (7 and the relative importance of snow

densiry (p). ths influence %-as espected on the HTC d u e s .

Conclusion:

In the durd summer after a wldfue and preceding the onset of thaw* air remperamres were

Iower in the burned treaunents than in the control. This sinration \vas hoa-ever rex-ersed atier the

commencement of thaw as the bumed ROW and the burned forest were - T C \.armer dian the

burned uench and the conuol ueaunenr.

=\s a result of the remol-ai of the uanspiring vegetation, relative humdiry \vas lower over the

three burned treaunents. Tree remord reduced surtàce roughness and aïfected u-ind speeds b!-

permitting greater u-ind velocities in the burned ueaunents.

Followng fie. the radiation budget of the burned surface \ras hndarnenraiI!- altered.

Burning creaced decreased albedo tfom burned surfaces which resulted in an increase in net

radiaaon. Consequend!-. soil temperanires were warmer in the burned forest and bumed ROW

treatments. This prompted the movernent of the O°C isodiem 60 cm deeper chan in the control

treatmen t.

Burning aiso drered snowpack characreristics. Snom~acks were g e n d y thinner and denser

than d u ~ g pre-fire conditions. This w a s a direct resdr of the rernot-al of t-egetation whch ta\-ored

snow redistribuaon and erosion by wkd. Borh cransport corridon eshibited slgns of snowpack

thinnrng as a result of the increased fetch distances. The most significant posr-he modification of

die s n o ~ a c k was a reduction in die variability of snou;pack characteristics ben.-een the uansport

corridors and the adjacent bumed forest areas.

HTC (Hea t Tram fer Coefficient) d u e s were lowes t dong the transport corridor. Two

exceptions w-ere however noted: the center pomon of' the east-west orienred R o b ' and the western

edge of the north-south orïenced ROW had the hghest HTC values. Wthm the bumed forest sires.

the highesr HTC cilues were recorded at leading edge sites. The highesr HTC d u e s of the burned

foresr were greacer dian a i l but one of die ROW sites. This suggests chat sites in che burned foresr

and on some areas of the ROWs u-ouid be poorl!- insuiared and be subjecr to coider soil

remperatures. This would aiiou; frost penemtion to greater depths. The active layer and the top of

the permafrost u-odd cool ro a grearer degree than orher treaunencs. This could rempordy offset

the summerume \rarming rhar results from increased net radiarion ot-er the burned uaunents.

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Geography, Tmt Cnk-ersin-, Peterborough. Canada 114 p.

Brown

Brown

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Haag R.W. and Bliss LX. (1974bj. Energy budget changes foilo~ing surface disturbance to upland

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Jackson C.I. (193). insolation and albedo. . \ l tGi l /S~bu~t iL. RJ-trln%ip.er. 5. 103 p.

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Johnston G. H. (1973). Ground temperature masuremats using thennocouples. In Promdng~~ ot'u

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Lafleur P. and Adams P. (1986). The radiation budget of a Subarcuc woodland canopy. :lfi-til;

1-01.39. Xo.2. p. 1.2- 176.

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-.lppled .\leteorufog. 1'01.12, p. 1359- 1366.

Chapter 3: Soi1 properties and thaw depth foliowing wildfire in a Subarctic u p b d forest and

on a simulated transport comdor

Introduction:

In Canada. permafrost Is present in various foms over alrnost 50'0 of the country

(Heggmbocrom 1995) and its presence creates unique e n g i n e e ~ g problems. It was quickly

recognized that the main concem facing northem derelopment u*as the degradauon of thaw-

susceptibIe. ice-rich permafrost u-hich can cause increases in active layer depths. thermokarst

subsidence and mass movement (Broun 1 !)?O. French 1976).

K'ildtires are one of the most important disnubance affecthg permafrost and vegerauon in

the subar& region nïereck 1973 a). -3 number of srudies hare been conducted on permafrost

condiuons follosing widfïre ( H d r t A 1978. Heggmbonom 19-2. 1973. Slackay 1977. 1995.

Viereck I973a.b. I'iereck and Schandeimeier 1980) and although resuirs have been rarïable, it is

generdy agreed that active Invers are thicker in the successional stands atier Fie than rn the adjacent.

un burned areas filacka' 1970. 1995. \'iereck 1973a. 1983).

Brown (1963. 1983) stated thar the heat produced by the tGe generally has litde unmediare

effect on the thickness of the active layer smce the orpnic layer seldom burns to permafrost depths.

Follouing fre. it is the change in surfàce albedo and the removal of vegetation that prornotes

wanner sod temperatures and deeper thauing.

Pubiished results of permafrost-uddfrre srudies have becn mainiy conducted in -\laska (Haii

a JI: 1978. I'iereck 1973a. b. 1982. I'tereck and Schandeimeier 13811, \Yek 1971) and in the

continuous permafrost zone of Canada (Heggmbottom 1971. 19'3. Macka!. 19-0. 19". 1995. K'ek

and Biiss 1973). There are no reporred results conceming the effects of uiidfves in rhe

disconcinuous permafrost zone of Canada. This paper \dl address rome of t h lack of information

by presenting some results of the short-rem effects of uildtve on the active la!-er rhickness of a

simulated transport corridor and adjacent burned forest.

Objectives:

The objectit-es of chs smdv n-ere:

il Compare the active layer depths and the sod moisrure contents for the rarious SEEDS

treaunents foiiouing burning.

2) Compare the post-tire thau- depths and moisme content changes for the SEEDS ueaunents-

z i ) Quanti+ the active layer changes of a bumed black spruce foresr in discontinuous permafrost.

Post-fire modifications of the active layer:

In eastem .ilaçka, ar the end of the Grst sumrner of an -\ugusc he . Lorspeich (.; J/. (1970)

found no significant differences in active iayer depths. Both bumed and unburned sites had rhawed

to depths of -70cm. Wein j1971) reporred an increase of 130-150° O in the deprh of the acuve layer

Li a l > - surnmer after a f i e die prex-ious year. However. dus difference had deched to 1 15- 120' O bv

the cime masïmum thaw \vas rached in the td. Brown et di. (1969). reported increases of 140- 160' o

4 years after a fïre in a black spmce forest. -4ddiuonaUy. rhey iound increases of 141-152°~ in thaw

depth in a 1-year-old burned area in centrai .ilaska. For the \~ïckersham Dome f k of 19'1. Fiereck

(1 973 b) reporred no slgmficanr differences in thaw depth benveen bumed and unburned stands

during the t'di of the Grçr sumrner after fixe. Hou-ever. during the tollowing thau- season. thawng

progressed deeper Li the burned chan in the unbumed stand .\lthough snownelr occurred 2 weeks

eariier in the burned stand thawing u-as sunilar in both sites und - lune. Beyond ths date. thatsing

progressed more rapidly in the bumed area. -4 masirnurn thaw- depth of 63cm u-as anained in rhe

bumed stand b!* 23 .\ugust. l l ashurn thaw in the unburned srand \vas attained on 6 September and

onl!- reached 4Ucm. Thus. rhawing in the burned stand was 137' O greater rhan in the unburned

(l'iereck and Dymess 1979).

Regarding the 1968 uïidi-ïire at Inul-k. N\\T. Heggmbottom (19-1) reporred no significanr

deepening of the active layer after rhe fmr surnrner. However. by 1970. rhaw depths in the burned

areas were 9 cm deeper than in the unburned. hiackay (197t)) menuoned much grearer increases in

chaw depth for the same period. By the end of the t i r s r surnmer afrer tire. rhe average Licrease of

thau- \.as 24.1 cm. representing a 149' O chickening. Thaw- depths had incremed co 34.8 cm ( 17 1' O) b -

die end of the second summer. In a follow-up smdy. l lacby (1993) re-esamined rhe originai sites

from 1970 and found rhar some sites had been esperiencing acuve laor increases und 1988. He also

nored chat there had been aggradation of permafrost during recenc years. perhaps as a result of the

shading effecr of the t-egetauon. More irnportan*. llackav showed char indiridual site characteristics

played an imporranr role in the development of the acnt-e layer. Some burned hummock sites. had

active la!-er increases bem-een 9-20 cm d u ~ g the 1968-1993 period. This was less increase than in

some of the unburned sites. Ir is important to note char thaw depth was nor monirored each year and

so it is possible char the ma-sîrnum post-fie thaw depth \vas not recorded. Permafrost ma? be

aggrading at the site and the values reporred my Slackay (1993) mav therefore be shailou-er than the

ma.sïmurn thau- depth.

Post-fire modifications of soi1 moisture contents:

F m srudies have been able to quanti- and dratr- detintte conclusions on the soil moisrure

modificaaons induced by d d f u e . -4 number of variables affect soil moisnue content and therefore

d e it difficult to quantifi- annual and seasonal variations. In non-&e conditions. soil moisnue

content depends on rates and volumes of soiid/liquid preapitaaon. rares of sno\tmelt, soi1 texture,

etc. -\dditionailv. the presence or absence of vegecation. its type and densin uill also affect soil

moisnire through various rates of evapotranspication. If the effects of ddf ï res are added to ths

already extensive tist of variables. the s p a d and temporal disuibucion of soil rnoisnire dramacicalh-

ïncreases in cornplesln and. therefore, renders seasonal cornparisons of soil moisrure contents

equally cornples. Comparing moisrure contents quicldy becomes an esercise of g r o s escimarion

rather than precise recording. 3ionetheless. some generai conclusions have been drawn from

previous s tudies.

The effect of fue on sod moisnire content seerns to depend on the sa-erin of the h e . the

type of soil and the nature of permafrost present (l'iereck and Schandelmeier 1980). number of

smdies have reported increases in soil moisture a short cime afier burning. (Kane e t k 19.5.

&uchkov 1968. Swanson 1996). It is genetallv agreed that these increases are due to permafrost

melting as a result of the rupmre of thermal equilibnum. i+-uchko~- (1968) argued char. in Sibena.

the increased moisnue hvored rapid plant growh char ultimately caused shalIower acal-e Iayers.

L n e et d (1 975) and Kers hau- and Rouse ( 197 1) suggesred the Uicreases in free surface u-a ter u-ere a

result of reduced e\-aporranspirauon thar tollowed removal OP the vegetauon. However. on sites with

litde organic material remaining aker h e . moisture contents ma!- be Lon-er. In lichen-u-oodland sires,

Kershaw and Rouse (1971) found that moisrure content-; \vere lower and flucruated more than in

unburned sites. The!- attnbuted ths difierence to increased rates of evaponuon fiom the esposed

mineral soi1 in cornparison to lîchen layen thar tend to retain moisnrre and reduce tlus fsorn the sod.

Smdies comparing decade-old surface disrubances found general trends of sod moisrure decreasr

when cornpared to undisturbed areas. The degree of change benwen these sites \vas highl!. variable

and depended IargeIy on individual site characteris tics (Lawson 1986).

More recendv. Swanson (1996) presented data sugges~ing that post-tue moisture contents

do not change predictabl- and that one of the major controls on moismre content \vas microsire

characteristics. He obsen-ed thar sods ~ 7 t h permafrost on the coldest and wettesr landscapes

(concave to plane. lower dope positions and north-facing midslopes) usuaily fded to thaw deeply.

with no substanaal changes in moisture conditions. Soils with permafrost on convesiues. crests and

shoulders and east-.west- or south-faang midslopes thawed deepl!. in some instances and not in

others. presumably as a hncuon of €ire severity or frequency.

59

Field methods:

Frost pro bing

In 1986. four p d e l frost probe transects were established a t the SEEDS site. These

transects crossed the site from a-est to mst and were used to monitor the progressive inaease in

a&-e laver rhïckness during the thau- season (Gallinger and Kershau- 1988). niis semp was used

Gom 1986 u n d the 1995 wddtire and several sm-eys were conduaed annualiv. In 1996. a new

nework of probe sites \vas irnplernented. this cime with nr-O uansects. -\dditionallv. a second

ne&,-ork of probe sites was set-up in an unburned stand of Pitw r n m u n ~ Iocated -3 km north of the

SEEDS site. This area has been used as a control since the begmning of the 1996 thm- season.

,%ch-e iayer depth measurernents were coliected using a soiid 3-rn-long and 1-cm-uide s d e s s steel

rod graduated in 1 cm increments. -+ sunilar 3-m-Iong probe \vas also used in areas u-here acu\-e

layes deprhs esceeded the probing capabilip- of the shorter probe. The technique used is described

by Mackay (1977). where the posiaon of the O0 C isotherm is inferred by probe refusal. indicating

chat frozen ground has been reached. &lacka!- (1977 discussed the potenaal errors associated uith

this method. Narnel~ that probe reiecnon can occur well abore or belou- the 0' C isotherrn

depending on soil testure. To address this potenaal error source. a third npe of probe was used in

1997. It consisted of a hollow. 2 m-long and 1 cm-wide s t d e s s steel rod where nx-O type-T. U-

p a g e therrnocouples were inserted. The therrnocouples were connected to a dual display digital

therrnomerer (mode1 Omega H H 1 C ) (Figure 3-1). Because of the long thermocouple calibracion

cimes required. ths probe \vas used at every fit& probe point dong each transect. Th~s permitted the

verificacion of temperarures when rejeccion depths were reached. -4 margin of O.I°C was deemed a

suffiaent indicaror of m a - h u m thaa- depth. This m a q n \ras also considered to be within the range

at which the zero-curtain/frozen t'ringe effect can occur (Rouse 1976. Hinkel and Nicholas 1995.

\Kïlliams and Smith 1989). Benreen 1986 and 1993. the number of probe sites varied from 339

(1986) to 361 (1993) due mainly to the extension of the mnsect lengths. In 1996 and 199.. 37 probe

sites were used dong each OF nvo transects on the SEEDS site. -~dditionaiiy. 50 sites were probed in

the conno1 treacment. Probe site spacing raried from 10 m on the ROK's and in the burned Forest to

0.5 m across the uenches. Due to tirne and Iogtsacal consrraints. the thaw depth \vas usudy not

monitored beyond the third week of .iugust. This prevented recordmg of the maslmum thaw depth.

Nonetheless. ir has been shown chat 90'0 of acave layer thickness is attauied b!- late ,\ugust and that

a v e q small increase usudt' foilows O'iereck 1982).

Figure 3-1: Permafrost probe (right) and permafrost/temperanire probe (left) used to mesure thaw depth in 1997.

Soil CO*

Soil moisnue contents and partide size/te ' rm u-ere detemrined from soii core.; estracted

€rom rhe various SEEDS ueaanenn. Coring was performed ores a four day period in May and

A u p s t 1997.1 total of 32 cores were exuacted during these penods- In each rreauncnt. sarnple sires

were randomly selected. .\ totai of 8 cores were esuacted from the uench, 4 korn each RO\Y. 8

from the bumed forest and 4 from the control matment. The sampitng was performed nith a hand-

dm-en corer sunilar ro char descnbed by ZoItai (1978). -in effort u-as made to estract core segments

of 10-13 cm. This u-as not alu-ays possible and core segment length varied from - to 21 cm.

Foilouing exmiction, sarnples u-ere prompdy bagged and kepr cool. D u ~ g the -\ugusr c o ~ g

period. samples u7ere werghed a few hours after esuaction.

Laboraton; methods:

Moisture content and testure analvsis:

hloisrure content \vas decermined b!- u-eighmg ';amples in the field and q p n after being

oren-dned ar 105 I 5" C ( K a h and lfaynard 1991). Moisrurr content \vas espressed on a \ver

weighr basis !total moisturej thereb!- avoiding awkvard moismre conrents of more chan 1 0 0 ° o

Ts\-tovitch 1975). Tord moismre was calculated using the foiiowing formula:

Tesnue analysis was performed using the Bococous hydrometer method as ourlined in Kaha and

hfavnard (1991).

Staasucal analysis:

Due to the small sample sites obtained during coring. stausucal analysis of moismre

conrents Kas not possible. Howe\-er. the thaw depth sampling was sufficient and stausucal analysis

u s performed. The data were compiled using the Slicrosoft Escel spreadsheer program and

srausacal analysis was perfonned using the SigmaStat analrsis package. -4 combination of the Escel

and SigrnaPlor programs were used to graph the data.

The data were 6rst tested for norrnaiiry using the Kolmogorov-Srnurioff tesr for goodness-of-fit.

N o n - n o d disuiburions were in (nanual logarithm) ms tor rned to meet criteria for pararnetrïc

staasticai anaiysis. One-way anaiysis of variance (,LNOI-,lj \ras used to test for significant

differences in mean maximum thaa depths in the three SEEDS ueaunents. \\%en significant

differences esisted mulaple cornparison cesring (ïuke!-'s test) u-as used to isolate the differences

benc-een groups. Both pinvi~-e and ~ x i o n ~ m i testing was used.

SemnLJIpo~~r-fi m o i ~ t m '.ontent m d ~#i~~nL.crr tinrn rbe i onrd tnutment.

In 1997. during the spring coring penod. the maioriry of sarnples eshibited some type of

risible ice, generally comprised of smaii cryais or tbkes. In a few isolated cases. longer (Ï-8 cm

long) core segments were entirel! compnsed of "ciean ice" (=\ppen&- .A). These ice Iayers were

obsen-ed in cores onginating from the burned foresr and the RO1X-s. S o ice lenses/ceins were

encountered during c o ~ g of the trench sites. aithough smaii ice cryscals. were seen . In the control

area. no ice Ienses. were encountered. During the lace summer coring penod ice of arîy n p e (reins,

intersaual, etc.j usas conspicuousIy absent from cores esmcted from the RO\Y sites. Cores for t h s

penod usualiy did not esceed - 150 cm. These were entirel!- mithin the acuw layer. Hou-ever. frozen

silts and in&\-idual ice cn-stals were present in cores from the burned forest. \vhere they peneuated

the permafrost table. -4ii cores eshibited high amounts of escess free water in the upper 90-100 cm.

The ody exception was the conuol ueaunent where escess \vater \vas prcsent in the upper 53 cm of

the soi1 column (Figure 3-2 D) (Table 3-1).

The burned forest eshibited ma-ximum moisture content in the upper 60 cm where morsture

varied benveen '2'0 and 30' O . Belou- 60 cm. moismre content remained benveen 20" 11 and -KI0 4 1

(Figure 3-2 .A). The uppcr 1U cm a-ere 3' O dqer than the conuol. Hou-et-er. benveen 20- 1 lu cm.

moisture content \vas at least 12' O tugher than the control (Table 3-3).

Figure 3-2: 199' posr-tire mean soi1 moisnue contents in A) Bumed Forest treament, B) ROW treatrnent, C) Trmch rreaunent and D) Control rrearmenr. Cirdes represent mean values and error bars represent standard dmiation.

Table 3-2: 199' post-fke differences in moisture coateot (O.0) berneen the burned treamients and the conuol at various depths.

In the R O K cores, mashum moisture contents reached 56'0 in the top 50 cm (Figure 3-2 B). -1

steady decrease followed to a depth of LM c m (20°0 moisnue). ROW moisture in the upper 10 cm

was 19'0 less than the control (Table 3-2). Below 20 n ROW' cores were werrer than control. The

maximum difkrence occurred at 60 cm depth (3 1 'O) (Figure 3-3 B).

In the uench. moisture contents decreased more rapidly &an for the ROW. .i max.knum

moisture content of 66' o \vas recorded at 20 cm and decreased to 2 9 O O at 110 cm (Figure 3-1 C). The

upper 10 cm of the trench were 1 j 0 o +er chan the conrrol. Below 20 cm. moisnire contents

evceeded the control values by at least 7'0 (Table 3-2).

The newly-esrabiished control treaunent had moisnve conrents that sreaddy decreased with

depth. Maximum moisture \vas 74" O in the upper 10 an (Figure 3-2 D). Surface moisture (0-10 cm)

was greater dian aU burned treatments. Hou-mer, below 20 cm, die conuol treament had lower

moisnire contents than the burned treaunents (Table 3-3).

PR- U J - . , O O J J I ~ ~ ~ ~ rhmge~- in moihtre ~untenf.

The s m d sample sizes obtained from soi1 coMg did not permit rîgorous statisacal t e skg

of the data. Nonerheless. a graphical representauon of the results p k n e d visual assessment.

Follouing h e , moisnire conrents generally decreased for ROT' and bumed foresr ueatrnents whùe

there was an increase in the uench (Figure 3-3). For alI three burned sites, moisture content in the

upper 15 an decreased by at least IO0 O from pre-Eire nlues. In the 15-30 cm depth range. moisture

contents for ROW and trench were again lower than in pre-€ire condiuons (-1 I0,o and -5'0

respecavely), whilst only the bumed forest had increases in moisture content.

Below 30 cm, uench moisture content was greater than pre-hre values. -\ rna,xknurn increase of

-18?0 was reached in the 105-110 cm depth range (Figure 3-3)- The burned forest had iow-er post-

hre moisnire contents below 45 c m depth. ;\ maximum decrease of - 12'0 was attained in the 60-

75cm range. Finallr. post-6re rnoisture in the ROB- cores decreased throughout the soi1 column.

Below 60-75 cm, moisnue content was sunilar to pre-tire conditions with differences of -3'0 to

0.8''o.

POJ-I$-R ~ -ea romi 2frln'rlf~on~- in mem rnc~iimzm ~huw dcpfh.

In 1996, mean maximum thau; depth for the burned forest, ROW and trench were 83 cm.

113 cm and 112 cm respectix-el>- (Table 3-3) (Figure 31). In 1997. meui maximum thaw- depth had

increased to 93 cm for the bunied forest, 136 an for the ROK' and 156 cm for the trench. This

constintted an inaease of 1 loto for the burned fores5 21°'0 for the ROW and 38O'o for the trench

over the 1996 values (Table 3-3) (Figure 34) . Thaw depth &-as 113"o. 31 1' O and 2-11 O greater than

the control for the burned fores& ROW and trench treatments respecat-ely. series of t-tests were

used to compare thaw depths becween creaunents for both post-tire thaw seasons. In order to

compare the n ïo datasets. the last probing of 1996 Ci .iugust) and the second-tast probing of 1997

(8 ;\ugust) were used There w-ere significant differences in thaw depth for burned forest and trench

sites. No signikant difference esisted berween years on the ROW qable 3-4).

Table 3-4: Results of t-tert comparing thaw depths of each burned umtment for the y . r s 1996-199'. 1-dues are b (n~turallog..) transformed. 1996 data are Erom Kershaw (unpublished).

Burned Forest 1996 vs. Burned Forest 199' ROB' 1996 vs. ROPC' 199-

Trench 1996 vs. Trench 199-

PR- L'C. p o ~ - t j i ~ ~ w + i t i o t ~ ~ - in mem ntr~~irnz~rn ~baw &lh.

.Ul post-fie SEEDS ueatmenrs had increases in active layer depth. The 1997 probe depths

were corrected for surface subsidence, thereby increasing the absolute thaw depth values. \\%en

compared to 1986 t-dues, mean masimum thaw depths for 1997 were 243.3°r~, 258.8' O and 203.3' O

greater for the burned forest, the RO\Y and the trench respectively (Table 3-3).

One-way analysis of variance (.kiOV-i) revealed significant differences in mean maximum

thaw depth arnong ail ùuee ueaunents @<0.001) during post-tire years (Table 3-5). Subsequent

multiple cornparison resting revealed signi ficanr di fferences benveen thaw depths in trench and

3.32 135.00 0.02 Yes 2.00 41.00 0.05 So 3.4- 38.00 0.00 1 \+es

Trench ROW Bumed Forest

Figure 3-3: Differences in mean soil moisnrre contents benueen 1991 (Solte 199 1) and 1997 for the SEEDS treatments

burned forest sites and between R O K and burned forest treatmencs @<0.05) (Table 3-6). No

significan t difference eUs ted benveen uench and ROK treatments. In 1997, subsidence-conected

values as weU as raw vaiues were used for tesMg. In bodi cases, patterns s& to chat obsemed in

1996 ernerged: painvise ces ring of ROW vs. burned fores t as weii as uench vs. bumed fores t rmealed

significant diffkrences in chan- depths whilsr no significant difference existed berneen ROX* vs.

trench pairs.

Table 3-5: A..-O I ;-I resuits compmïng 199' mean maximuni thaw depths amoag Bumed Forest. ROW, Trench and Control treatrnents. 1-dues are In (nrtturaf hg.) trmsformed.

Table 36: SIultiple cornparison test ( T u h i tcrl) for pairs of mean mauimurn thau; depths in the three burned treatments (8urned Forest, ROK', Trench) and the Control treatrnent. .U cornparisons are based on In (n~ruruf hx.) transfonned data.

Trench vs. Burned Forest Trench vs. ROW RON' \-S. Conuol ROW vs. B m e d Forest Bumed Forest vs. Control

Discussion:

The graphic representation of the acave laver in lare summer (1996-1997) indicared that

parterns of thaw were relaà-el? conscanr during these w o posr-tire years. The principal difference

being che magùtude of thaw which \vas greater for the latter year. Each point on the graph

represented the mean maximum thaw depth for each probe site averaged for the w o transects. The

vears 1996 and 1997 were plotted with values that were not corrected to account for total

subsidence, since these data were nor available in 1996. This generalization of the position of the

frost rable is probab- not an accurace representation of the acnral fieid conditions. The averaging of

values benveen transects has certainly attenuated some of the micro-site rekted rariability of the

0.545 4 9.982 Yes O. 15 4 323- S o

O.--- 4 14-16 Yes 0.395 4 '-509 Yes 0.382 4 9 - 5 9 Ses

rhaw depth.

Pre- vs. post-fire changes in mean moisture content

FoIiowmg Gre, the rnoditied eneqg baiance at the ground surface usually -ers the melting

of ground ice. This is particdariy pronounced in areas of thaw-susceptible, ice-rich permatiost such

as that presenr ar the SEEDS site. .\ssociated mith this meiting is an esculsion of ground-ice

rnelmter and assockted ground subsidence (Collins et clj. 1994. Mac+ 1995). The rha\suig of ice-

rich permafrost adds water to the bottom of the active layer. This arnount ofwater is thought to be

approsimarely qua i in volume to the arnount ofground subsidence (Mackay 1995). In surnmer. pore

w te r €rom the thauuig active layer can migrate dounwards under a temperature gradient and

rerfeeze around the posiaon of the seasonal permafrost tabIe (Parmuzina 1973, Cheng 1982, Mackay

1983. Bum 1988, \ . - i s and Smith 1989).This resulrs in an inuease of ground ice at these depths.

This mechanism can esplain the changes in rnoisture content obsen-ed ar the SEEDS site.

-PoJ-t-jire d r $ ë ~ n r ~ ~ - zn moh-t~tn c o n t ~ t between tfp~trnent~-:

The decrease of post-fie moisnire content belon- the organic layer ((15 cm) foiiowed the

progression of the deepening of the active layer. The slgniticant differences in moisture content

benveen the uench/bumed torest and RO\S'/burned forest were the result of the age of the

drsnirbance and the rime since thaw progressed beyond the pre-disnubance active layer depth. The

age of the disturbance also esplained the lack of sqpifcant differences benveen RO\S'/Trench. Both

sires were affecred by a disrurbed energ'- balance for 8-9 years more chan the burned forest. Because

of h a . permafrost melred and meInrater drained from these areas in g a r e r amounrs and for longer

penods han in the burned torest.

- Po~-t-jire di$C.renm fin moz~-rxtrp ~antmt Itetwten bzmed crnd iontroi' tnwtntentx.

The differences in moisture beween the control and burned treaunents resulted from the

post-he modification of the evaporaave regirne as weU as slight differences in the parricle size

distribution of soils among the sites. The moisnire decrease in the burned ueatments was related to

the rhichess and colour of the remaining organic layer. In the burned forest and the ROK-S. there

was a hnning of this moss/pear layer as a result of being consumed/osydized by fie. ;\ddiuonally.

the decrease in aibedo led to increased surface temperatures and greater races of evaporauon, thereby

l o u - e ~ g the moisture content of these organics (Rouse and Miils 1973.

Since both of these ueatments still contained their organic iayer. it would be reasonable to

expect similar levels of moisture tklthin this layer. Wh!-. then. were the moisrure contents so

markedly different? The greater decrease in rnoisnire of the RON' u-as Wiel- related ro the near-

surface ground ice content. It is important to remember thar t h s cornparison uas based on nvo

ciarasets coiiected 7 years apart and that the ROSS were undergokg permafrost degradauon before

the fire. Consequenciy. the melting of exess ground ice and the runoff of this meInrater Iowered the

moiscure contents of the ROW ueaments. The difference in pre-/post-he moisrure contents for

this t r a m e n t did not indicate a large decrease. .ilthough chere is no way of et-aluaung the runoff

that has occurred. the arnount oiground subsidence obsewed berneen 1990 and 1997 (Chapter 4)

confïrmed that excess ice has been removed. In the trench, the orgarilc Iayer was elimrnared during

construction and cannot be invoked as a controilmg factor on near surface moisnve contents. -\s

was the case for the ROWs. ground subsidence suggested that escess ice melted from the upper soii

column, par$- e-tpiaining the lou-ered post-lire m o i s u e contenrs for these depchs. More likely. the

lower post-tkie moisrure \ras a resuIt of a sampiing bias. During coring, core segments could not be

exuacted from water-logged areas as suction developed because of melnt-ater CiUuig the u-hole. This

resuicted coring to elevated (and therefore dryer at the surface) sites within the uench where a core

hole could be staned without coliapsing. -As this uas the only wa!- of extractïng cores from the

trench. the method had to be used despite the bias. This explains the presence of lower rnoisture in

the top 10 cm of the uench.

Below 20 cm, ail b m e d tremnents were wetter than the conuol as a result of a difference

in particle size. The SEEDS treatments wcre composed primanl!- of silts and clays. sometimes

containing fine to coarse sand i-Ippendk -i). In the conuol creaunent. the silt-clay h c a o n \vas

Iower and coarse sand \vas more abundant. The f ier material in the bumed treatments offered

op tha l conditions for u-arer sanirauon and the developrnent of segregared ice. The poor drainage

imparred b!- these material T e s fa\-oured hgher rnoisrure in the SEEDS ueaunents.

Pre- vs. post-fire variations in thaw depth.

Bltrned Forrit/ h - / i r P Contrai

Since the creation of the SEEDS site in 1986. there have been significant differences in chaw

depths among the three treaunents (Gallinger 1990, hiolte 1991). In 1989, the conuol forest

(undisturbed by clearingi had arrained thaw depths chat were h o s t 20 cm deeper than the 1986

measurement. Nolte(1991) and Seburn (1993) reported an apparent stabhzing trend for the Forest

sites as early as 1988. This srabilization was relatil-elv constant from 1989-1992. Seburn (1993)

reported no significant change in mean maximum thaw depth for this penod. The initial increase Li

thaw depth (1986-1987) may have been a product of the establishment of the fint probe neworks

where localized foorpaths developed. This resulted in a compacuon of the surface organîc cover.

therebr uicreasing the bulk density and thermal condu&-in- of the soi1 (Goodrich 1983. Lawon

1986). This would seem pkusibk. more so since the sarne foorparhs were s a risible foiiowing rhe

hre. increase in thau. deph in the bunied forest u-as recorded during the nvo than- seasons

foiioauig €ire. In 1976. thaw depth reached 82 cm. an increase of 23'' O over the last recording (1992)

and 91' 0 over the initial 1986 vdues. In 1877. thau; depths reached 93 cm. r e p r e s e n ~ g an increase

of 37' O over the 1992 pre-fiire probing. These d u e s did not take into account surface subsidence at

the site. Only the 1997 d u e s could be correcred for subsidence. Mean subsidence in the foresr --as

calcuiared at 38 cm (Chapter 4). Sfean subsidence-correcred thas- deprh becarne 131 cm

represencing a 108' O increase over the 1986 thaw depths. Slnce subsidence has most kely been

ongoing ar different temporal and spatial rates. only a cornparison \~is i th p r e - c l e a ~ g values is ralid.

The lack of data on the degree of subsidence that has occurred annudi! ben-een 1987 and 1996

renders an- cornparison with 1997 data precarious. However. given the reduced rate of thaw depth

increase and the lower moisnire content wifh depth. it may be safe to assume litde subsidence

benveen 1990 and 1993 pnor ro the fire. If one acceprs this. &en a l increases in thaw deprh u-ere

due to the 1995 wddflre and took place over three thax seasons.

The post-fie increase in thau. depth u-as not unespected The disturbance created by the

f i e modihed the enerE balance of the surface and the resuhng increase in thaw depth \vas an

expression of these microchatic moditications. The 1995 fie did not consume ail of the orpnic

mat. The degree of bum was variable rhroughour the site and an orgaruc layer (1(?-15 cm rhick)

remained in the forest and on parts of the RO\K*s. The p ~ c i p a l modihcauon to this surface \vas a

substantial increase in albedo (Chaprer 2). The insulaung properties of the organic mat have been

discussed b!- numerous aurhors (Luthin and Guymon 1974. Zolrai and Tarnocai 19-5. Riseborough

and Burn 1988) =-ho agreed that the persistence of sporadic and some discontinuous permafrost

u a s closelv related to the thcimess and moisrure content ofthese organics. Fol lo~ing rue. decreased

albedo and increased moisnire contents due to ground ice melcing have tncreased the thermal

conducrivi~ of ths layer in the early part of the melt season (Farouki 1986. L n e r.t i 19-5;.

resulüng in the obsen-ed increased tha\v depths. .iddiuonnaffy. rhis increased thaw depth \vas h k e d

to the removal of the tree canopy and the ensuing increase in incoming shornt-are radiation. The

open-canopied forest present before f i e u-as completel- remored. .ilihough sparse. the pre-he tree

cover buffered the incoming radiauon by possibly absorbing and/or retlecting benveen 40°0-'Go O of

this shomva\-e radiation (Chapter 2) (Haag and BLiss IX-la. Latleur and .idams 1986. Rouse and

M i s 1973.

R.l$Jt,--q:wg

Lmrnediarely a fter clearing. G a g e r (1 990) found thar mean rna.uimum thaw depth

inaeased from 1386 to 1989. From 1989 to 1991, Seburn (1 993) also found an Ïncrease in mean

maximum chaw depths. Probe data from 1991-1993 (Kershau-. unpubiished data) u-ere a p

indicative of chau- depth Licrases. This suggested chat the pemfros r uas s d degradhg eighr y r v s

after the initiai disnubance. In 1996 (Kershaw. unpubiished data)-1997. Lhere was agam an increase

in thaw depths.

The iack of signifcant ciifferences in thau- depth afrer 199 1 u-as reponed by Seburn (1993).

He noted rhat the 1990 mean masimum rhaw depth \vas -10 cm deeper than the previous year.

However. this uas not a signiticant difference @<0.01). In t 99 1. the ROW attained its greatest mean

maximum rhaw depth. orer 13 cm deeper than 1990. This constinired a sigmficant difference from

the 1990 thau- depdis (p40.01). prompting him to suggesr that die permafrost u-as r d degradmg

fa-e and sts cears after RO\Y creauon. (Sebum t r d. 1996,

The posr- f re actii-e layer rhickening of the ROUS indicared that permafrost degraded since

1986 and that the 1995 Cie had not accelerared the rate of degradation ro lerels greater chan those

obserr-ed m 1991. The lack of sigmficanr difference benveen mean masLnurn thaw deprh b e o n d

1991 suggested that the annual progression of thau- on the ROW's had stabilized and remained

relatirely cons tant even a fier fiire.

.\ rapid incrase m thau- depth \vas noted from 1986 ro 1990 as a rejulr of the clearing

disturbance I?;olre 1991. Noire and Kershau- 1998). D u ~ g ROW clearïng. the surface organic mat

was not removed but \vas trampled to rarious degrees Kershaw 1988). The b u a l increase benveen

1986-1991 uas probably the result of a rapid response ro this thermal ciisequilibnum. The organic

mat buffered some of the efiects of t h s new energy balance. resulung in a rapid <+5 !-ex)

stabilization of the annual increase of tha\v depth. FoUouing fxe. the organic Iayer on the ROK-s was

in a srate s d a r to that obsen-ed in the bumed foresr. The kck of srgnificant increase in mean

ma-simum thaw depth sremmed from the facr that the posr-fie r n i c r o c h a ~ c disturbance \vas nor

grear enough to orerwhelm the i n i d efkct of the clearing disturbance. .in increase in near-surface

soi1 temperatures was obsen-ed follouing tire (Chapter 2) but the thermal "inertia" of the rhawd

marerial of the active layer ke ly dampened and bufferred (Lunardini 1981. \Yfiams and Smith 1989)

any warming that could potentdy increase thaw depths.

T m - b e ~ -

From the tune of the first measurernents taken at the SEEDS site. it \vas clear that the

trenches were esperïencing the grearesr increases in mean masimum thau- depth. From 1986 ro 1989.

mean masirnum thaw on the uenches inaeased at a rare of at Ieast 30 cm a ' ^;olte 1390). -4

rempomry period of apparent permafrost aggradaaon u-rs reported in 1990 when thaw deprhs u-ere

shaUower than the previous year b - 14 cm. Sebum (1993) anributed rhis variation ro cooler and dq-er

climatic condiûons. as recorded at Norman K d s . NTT. From 199 1 to 199'. thaw depths remained

rekitively constant. Sorne caution musr be exerased when inrerpreung rhese data. In 1993. the

masimum thau. depch was nor recorded at aU probe sires. In panicular. ciara u-ere rnissing from the

mnch and probe h e s 3 and 4. This resulted in mean \-dues based on approslnately ' 4 of the rotai

probe sites. In 1996. the final probing was performed on 7 .\ugust. the earliesr of ai i probe dates

smce 1986. Ir w s reasonable ro especr that some posr-surr-ey chauing occurred: as rhese ralues were

certain- an underesrlnao'on of the mashum thaw deph Nonetheless. a panern was apparent for

die trench sires. The significant differences in mean masimurn rhau- depth for the years 1993 and

1996 ma- have occurred because of the rmaller daraset. Sebum 11993) and GallLiger (1990)

suggesred that permafrost degradation \vas deueasing as earI!- as 1389-1990 and that thaw depths in

rhe rrench u-ere srabking. The posr-tire thaa- deprh resulrs supponed this initial obsen-aaon. More

ïmponandy rhts indtcared thar the tire had a rery limired effecr on the diaw depths of the urnches.

It is probable rhar the initial clearing and trenchng dismrbed the surface to a degree fax esceeding

the disnubance lerel of the uildfue. During uenchmg. the surhce organic mat \vas compkrel!-

remored and subsequend- back-iied leaving bare mineral sod at the surhce. Thxs n-pe of surface

disnirbance \rns ranked amongjt the mosr damagmg ro permafrost (Heggmbonom 1973).

Heggmbotrom (19-3) also indicated chat the wildfue disnirbance \vas much less severe dian the

uenching. The rernod of dus important thermal bufferïng layer. resulred in increased ares of soil

hear flus and rapid thaw progression during the fvsr 2-3 years (Solte 1991:. S d a r resulrs have been

found by Hegginborrom !1973) and Iiereck (1982). Borh srudied post-fie rhav depths foiioning the

1968 Inuvili rire (Heggnbottom) and a hre in .ilaska n7iereck). Ther reponed rhaw deprhs up to 5U-

80'0 deeper Li areas disnirbed by the consmcuon of iuebreaks in cornpanson to areas afkcted b!-

wildfire. They concluded char the removal of die surface regetauon and the soi1 compaction from

repeared passage of he- machinen resulted ingrearer disnirbance than the f i e itself. Lawson

(1986) also found similar resulrs by using a Sei~e~g inde-Y fJC) ro quanue the degree ofpernirbaaon on

areas affecred b - disntrbances of r a e g degrees. Trampled vegetation had rhe lowesr severin- indes

and after 30 years. diese areas had Si ralues rhat were equai or less than before disturbance. .ireas of

killed vegetaaon had ralues equal to or sLghdy hîgher (lOOa) than for pre- disubance conditions.

Sedunent and regetation remol-al created increases in thaw depth of 10-250' o (Lau-son 1986). The

rares of licrease observed at SEEDS f d \~ithin the upper rang of Lawon's ( 1986) predicred values.

Spatial variation of thaw depth and influence of microsite characteristics

hficrosite characterisucs have often been recognited as determinuig factors mfluencing thaw

depths. In paracular, the pondmg of water in surface depressions has been shown to increase thau-

depchs dramaucdy (LmeU and Tedrow 1981. Nelson and Outcalt 1382, Swanson 1996). The

importance of chic flutio-thermal erosion was invoked b~ Gallinger (1990) as a means of expIaining

the lugh cariabdi- of thaw depths obtained at different sites. Water accumulaaons a-ere found to

preferentially occur in areas affected by deartng. P o s t - c l ~ g surface changes resulted in the serrling

and compaction of the back-ulled umch materiais which lead r o hear depressions compnsing

sections of ponded or occasionali!- flowing =ter. Because the trenches were lower dian surrounding

areas. rhey collected melnrarer. snowmelt and preapitation nuioff preferenriaü!. In post-he

conditions. numerous areas of ponded uater were obsen-ed in the burned foresr. whùe less w-ere

present on the ROK-S. .\ssurning chat a great deal of the variabili~ in thau- depth wts conmiled by

these areas of ponded \vater. the degree of skeuness for each site \vas used as a aa)- of a - a l u a ~ g the

change in distribution variabdip-. The degree of skewness from 2986 was used as "connol" values

for pre-disturbance variabilin- to which post-disnirbance/post-f~e rariability codd be compared.

From 1786 to 1993. all three S E E D S treaunents had distributions that were skewed to greater

degrees than in pre-Eue condiaons. Foilowing tire. skewness decreased co pre-fie levels or less.

This was parücularly striking on the Rom' where 1993 skewness tt-as 2.064 and 1996-1997 skeu-ness

was 0.782. and -0.00'41 respecurelv. This suggested that the variabilin- in the distribution of rhau-

depths had decreased likely as a result of surface subsidence and flattening of the ROW surfaces.

resulcing from the melung of ground-ice. In the burned forest. mcreased distribution variability =-as

obseri-ed und 1993. \-anabilin. then decreased sighdy in 1993. Post-fie data shou-ed thar n . r iabiL~

decreased alrnosr co pre-dismrbance levels. This posc-Fie change ma'- have been the result of a rapid

initial response of the burned foresc to the ne%- eneqp balance. Th.; process may be similac r o thar

obsen-ed in the trench benr-ecn 1986-1987. where variabilin- had decreased rapidly after the Fmt

year. as a result of the substantial energy balance change follouing cleaïing. .i rapid geomorphc

response was also obsen-ed bv Codv (1964). where surface subsidence in h u m r n o c ~ terrain occurred

only 4 years after h e , as a result ofground ice melting.

Conclusion:

Follouîng the 1995 uildfire. active laver response uxs variable rhroughout the SEEDS site.

The trench sites had the least post-Gre active layer increases. foiiowed by the ROB' sites and the

burned forest. The trench sites were lide affected b!- the d d h e as thau- depths were not

significandy different from the last pre-fie measurements and the 1996 values. Ttils suggested tu-O

77

possibilities: i) char the initial 1986 dearing and trenching process disturbed the sudace to a greater

degree han the wiidfire disturbance or ir) rhat rhe effects are sa l i being fdt and the fd response ha%

vet to be regktered The majorin- of the acave layer depths obsen-ed in 1997 were a result of the

initial simulated uansporr corridor distubances and kelv occurred ben\-een 1986 and 1995. The

ROW sites had low lnaeases in amive hyer deprhs. The post-fie actn-e l a~e r depths w-ere not

significan* differen t from depths observed a fier 199 1. .\gain. this absence of significan t inaease

Wiely stemmed from the degree of disturbance of the initial dearing of the ROWs, that superseded

the rnicrodimaac modifications caused by wildhre. The burned forest sites had sigmficant increases

in thau- depths. This was a result of the modi~cauon of die surface energy balance resultïng from the

burning of die orgamc mat and the rernocd of che uee canopy. This aiiowed thaw co progress deeper

into the ground-

Mean moisrure contents have decreased at all sites follo\\kg wildf~e. -\dditionally. there has

been an inaease in the variabîiip- of moisrure throughout the sod column. -4iI SEEDS treatments

eshibited decreased moisture contents in the upper 13 cm. This \\-as atuibuted to the buming of a

portion of the organic mat and irs decreased albedo \t-hch fat-oured greacer rates of evaporaaon. -\t

depths below. 15 cm, motsmre contents were again lou-er rhan in pre-fie conditions but there were

rapid flucruaaons in these amounts. These ducmations xvere interpreted as ephemeral active layers

that resulted from the migration of \rater to the freez;ng front during each thaw season. Such aras

of supersamted matenaf w-ere thought to be artifacts OF the progression of thau- foflo\~ing the

wdd frre-

References:

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in che Xorthern Cucurn~ohr Ecosrstem, RW. \ K i and D.,l >lacLean (Eds.). Scope 18.

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Hampshire, 13p.

Burn C.R. (1988): The devetopment of near-surface ground ice during the Holocene ar sites near

hfavo. Yukon Terrirory. Canada. journui or~Q11uret71ug SLiemr. 1-01 3. p.3 1-38

Cheng G. (1987): Effecr of uni-direction accumulation of unfrozen water in season+- froten and

thawed ground. KKW Toqbrlo. No.27. p.98+989.

Cody W.J. (1964); Reindeer Range Sun-ey 1957 and 1963. Canada Depanmenr of .ipculrure. Plant

Research Insuture. 16 p.

Collins C.M., Racine C.H. and Walsh M.E. (1994): The phrsicai. chernical and biological effects

of crude oil spills after 15 years on a black spruce forest interior .liaska. .-lnlii: i*o1.-I7.

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Farouki, O.T. (1986); Thermal Pro~erties of Soils. Series on Rock and Soi1 Xlechanics 1-oL 11.

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Human-Induced Disturbances on Pennafkost--\ffected Terrain, Occasional Papers in

Geographv Castlegar, Micheal C.R Edgel jed), B.c G t o g r i h i ~ d Senes. So- 46. p.2138.

Gaffinger BJ. (1980); Permafrost degradation and thennokarst processes assoaated mth human-

induced disturbances, Fort-Norman, WXT., XISc thesis. Depanment of Geography.

Cniversity of -IUbern. Edmonton. 338 p.

Goodrich L.E. (1983); Thenna1 performance of a section of che Mackenzie Highway. In: Pc.nn<th~-~:

Foroth In/ern(~tioncri Cocterentr Pmt-ecding~, Narional -\cadem!- Press, Washmgton. D.C. p.369-

373.

Haag R.W. and Bliss L.C. (1974a): Functionai ettects of regetaaon on the radiant enew- budget

of b o r d fores t. C~nrldrln Gc'ote~-hniLizfjo~~nr~~f' \-01.11. p.37+379.

Haag R.W. and Bliss LC. (19-1b): E n e r e budget changes foilowing surface disrurbance to

upland mndra. J O Z ~ B ~ q'.-fppfitd EL-oiog. ifoI.I1. p-335-374.

HaU, D.&, Brown, J., Johnson, L. (1978); The 197- rundra f ie in the KokoWi Rn-er a m of

-\laska, . 4rL.fjL-.3 1:5+58

Hegginbottom J.A. (1995); T P ~ J ~ ~ v J - ~ ' : .\utiond--lth~- ot'C~m& $1' Ehtion. 51ap > K R 41°F. Scale

1 :7.500,OUO. Nanual Ressources Canada, Ottawa.

Hegginbottom JA (1973); Some effects of surface disnubance on the permafrost active 1ayer at

I n u d . XKT, Ottawa: Environmental-Social Cornmittee Northern Pipelines . Tdik F o m on

Sorthem Oil Derelopmenr Rpport .\-o. '3- 76. 19 p.

Hegginbottom JA. (1 93 1 j; Some eitects of a fores t fire on die permafrost active Iayer at Inu~-k

NW T. In: Pmceeding~- ot'u Semindr on the Petmg/io,-t . - f ~!+c)r. Sarional Research Councll o f

Canada. -\ssociate Cornmittee on Geotechnicai Research. Ottawa. Technical llernorandum

No. 103. p.3 2 -36.

Hinket K.M. and Nichoias J.RJ. (1995); -icrk-e Laver Thaw Rares at a B o r d Forest Sire ui

central .%ska. C.s.-\.. . - bi-tfL- crnd - -i&ne hertnh. 1'01.27. s o . 1, p.7381).

Kaka Y.P. and Mavnard D.G.(1991); Afethods for forest soil and Ianr analysis, Informauon

Report NOR-S-3 19. Fores Canada. Northw-est Region, Northern F o r e s v Center. 101 p.

Kane DL, Luthin J .L and Taylor G.S. (19751: Physical vansfer pmcesses Li subarcric soils

uifiuenced by fores t fircs. In: Pmceedny Conte~nce on Soii- ICher Pmb/em- in Cdd Rrgiom-. .\h 6-

' 19-5- Calgarv .-Ubena, Canada. P. 128- 147

Kershaw G.P. (1988): \---End Repon 1987-88. Smdies of the Environmenral Effects of

Disturbances in rhe Subarctic (SEEDS). Department of Geograph?-. UN\-ersin- of -Ilbena.

Edmonton. 45 p.

Kershaw K A and Rouse W.R. (1976): The Impact of Fue on Forest and Tundra Ecos~stems-

Final Repon 19-5. . - L t ' R -F--6-63. Depanment oi Lndian .\fiairs and Nonhem

DeveIopmenr. Ortau-a. 54 p.

Kqvchkov V.V. (1968): Soils of the far nonh should be consened Pnroda !51useurn of soi1

saence. .\loscou. Stace Cnii-ersin.), \'ol. 12. p.-l--4. Translared in 1.Brou-n. \Y. Ricltard and

D. Vicror. Reporr # 138. Cold Regions Research and Engineering Laboraton. Hanover Sew

Harnpslure 13 p.

Lafleur P. and Adams P. (1986): The radiation budget of a subarctic woodland canopy, .-l);-lzc:

Yo1.30. No.2, p. 172- 1'6.

Lawson D.E. (1986); Response of terrain to disturbance: a sythesis of obsen-ations from northem

-ilaska. CS=\. .- lnti~. und -- lipinc' &.sean-h. 1-01.1 8 No. 1. p. 1 - 17.

Lineii =and Tedrow J.C.F. (1981); Soils and Perrnafrosr Sun-ers in the .\rcac. Clarendon Press.

Oxford, 217p.

Lotspeich F.B., Mueller E.W. and Frey P.J. (1970); Effecrs of large scalc forest tires on a x e r

qualin- in intenor .liaska. C.S. Department of the intenor. Federal Kater Poiiution Control

;\dminiçtration, -UasEra Rater Laboratory. Fairbanks. 155 p.

Luthin J.N. and Guymon G.L. (1974): Soil moisture-1-egetaaon-temperature relauonships in

central -ilaska, &mui of Hjdmio~. VoL23, p.233-246

Mackay J.R. (1970); Disturbances to the mdra and foresr w d r a environmmr of the Yiesrern

,Gctic. Cclncldiun Gr'ot~~%InlcirlJo~trn(~~ VOL 7 p.420-432-

Mac- J.R. (1 977); Probing for the borrorn of the active layer. In: Report of -1cuvities. Pan -4:

Geological Surr-ey of Canada Paper. 77- 1.4 p.32'-328

Mackay J.R. (1983): Donnward uiiter movement into irozen ground. western -1rcuc Coast. Canada.

Cmc~dirln journui or-Eu~h Liefifi-. \*o1.2(,. p. 1 2i 1- 1 34.

Mackay J.R(l995); -1ctix-e L a o r Changes (1968 ro 1993) folloming die Foresr-Tundn. FLe near

I n u r k NST. Canada. .-itl~il. md --llpim ~ J - ~ J T L ' ~ . 1-01.27, No.4. p.393-336.

Nelson F. and Outcalt S.I. (1982); -4nthropogenic geomorphology in Norrhern .\laska. Plpjid

Gr'ogrgb. 1'01.3. p. 17-48.

Nolte S. (1 99 1): Some GeoecoIogical Effects of Dis turbances on Sear-Suriace Permafrost

Characterisucs (SEEDS. WXT. Canada). Diplomarbeir am Fachbereich Geographie der

Phillips-Cniversitar. Marburg/Lahn, 167 p.

Nolte S. and Kershaw G.P. (1998): Than- deprh characterisacs over five rhaw seasons foilouing

ins raihaon O i a simulared transport corridor. Tulita. NKT. Canada. Pemgt;o~-t rlnd peng/rlLiu/

pmt-e~m-. 1'01.9, p. 00-00

Parmuzha 0. (1978); Cn-ogenic tenture and some characteristics of ice formation in the active

layer. Translated from Russian in P o h Georqlg u ~ d G e o i o ~ (1 980). 1'01.4. p 13 1 - 153

Riseborough D.W. and Burn C.R(l988); Influence of an o w c mat on the acuve layer. In:

Pnmrl/"~-t-Fozirtb Intemrlrzonui C o + x e Pm-eedngr. National ,\cademy Press. Xashington.

D.C.. p.633-643.

Rouse W.R. (1976): Microclimatic changes accompan!ing burnïng in subarcac lichen woodland . --in.rt;.and--l@ne Rr.~-r'~~r'h. 1'01.8. Pu'0.4. p.357-376.

Rouse W.R. and Mills P.F. (1977); .\ Classification of Fire Effects on the Microdimate of Forest

and Tundra Ecoy-s tems- Finuf Report. Emimnmentui .St~idie~- So .2 , Miuster of Indian and

Korthem .iffaus. Ottawa, 21 p.

Seburn D.C.(1993): Ecological Effecrs of a Crude Oïl Spill on a Subarcac Right-of-Ka!-. 5f.S~.

thesis. Department of Geography. Cniversity of -4lbena. Edmonton. 145 p.

Swanson D.K (1996): Susceptibrlin of soils to deep thalv iollo\ring foresr fves in inrerior .ilaska.

L*.S.-\. and some ecologc implications. --Ir&. ~ n d - - f/'im Re~wr~.h. 28. 3 17-23.

Tsytovitch N A (1975): The Mechanics of Frozen Ground, S~ïnzow.G.Ii. and Tschebotarioff.

G.P. Eds.. XlcGraw-Hill Series in hfodern Suucrures. Scripta Book Company. K'ashington.

D.C., 476 p.

Viereck LA. (1973a): Ecologtcd Effecrs of River Floodmg and Forest Fires on Pemafrosr In:

Pennajk-f-,\-orlh .-lmniim Contribrithn ro rhe Se~nnd Intmt(~tionui' Colf;.remr. National -\cadem!- of

Sciences, \'Cashmgton, D.C., p.60-67.

Viereck LA(1973b): Rïidfxe in the taiga of ;\laska. Jo~ t rnd cf211~temm h e u r i h . Yo1.3. p.465-495.

Viereck L A (1982); Effects of f ie and firehes on active laver thickness and soi1 temperatures in

in terior =Uaska, In: Penn+ut- FOI^ Cunudiun Co!/erenie Protwding~-. X Iarch 3-6. 1 98 1 .Calgary.

.ilbena. National Research Council of Canada. -\ssoaare Cornmirtee on Geotechnicai

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Fairbanks, =Uaska, CS. Department of =\griculture. Paatic Northwest Forest and Range

Experiment Station, 71 p.

Viereck L.A. and Schandelmeier L.A. (1980); Effects of Fire in -ilaska and -4djacent Canada -

a literanire retiew, CS. Deparunent of the Interior. BUTPLUI tf b n d .~l(~n(~gemtrt. --I/u&.

Teibnrd Rppod 6- 1 2-l p.

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Etaiog; 1-01-51. p.843-852.

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Cambridge: Cambridge Cniversiry Press. 306 p.

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Soltai S.C. and Tarnocai C. (1975); Perenniaii!- irozen peadands in the western ,ircuc and

Subarctic of Canada, Cclnlrdilrn J o z m d o/-Edrth S'7ent-t-i. L'oL 12. p.28-43.

Chapter 4: Thennokarst subsidence and seasonal /long-term terrain modifications following

wildfm and anthropogenic disturbance.

Introduction:

Surface subsidence as a result of thau- settlemenr consamtes one of the prinapal

considerations in norrhem engineering and exploration proiecrs. In regïons of ice-rich. thaw-

suscepable permafrost, surface subsidence may follow d l s ~ p t i o n of the ground. Thaw-ing ma!- be

initiated as a resdt of geomorphic. vegetational or chmatic modifications affrcung the thermal

equitibrium.

The magnitude of ground subsidence depends prirrady on the severin of die initial

disturbance as w d as the arnount and distribution of escess ice (French 1976. \l-rlliams and Smith

1989). The thauing of ground ice invol\-es an i n i d reduction in \-olume of 9O O. usuallv foffowed b -

an additional Ioss due to drainage of melnvater ~ ~ ~ i l l i a m s 1982). The uitimare amoum of sedement

uiu depend on the effective stress benveen soi1 particles. u-hich in mm is a function of the stauc

01-erburden pressure and the final pore water pressure +K'.ïarns and Smith 1989).

,\ comrnon rnanifesrarion of surface subsidence is the development of thermokarsr

depressions follouuig rapid increases in thaw depth. \Yilhams and Smith (1989) nored char surface

subsidence could be a positive feedback mechanism when it allo\t-ed thawing to progress deeper.

leadhg to more subsidence. -\s thennokarst develops. water accumulacion in surface depressions can

subs rantiall!- increase thawing depths Kerfoot 1973. Swanson t 996).

Paar smdies of uildfires and permafrost have reported va+g rates of surface subsidence.

Follo\ting the 1968 tire at I n u d . Northwest Territories. in a regron of continuous permafrost.

Hegginbotrom (1971) noted subsidence of 19 cm. This Kas coupfrd nith a tlatrening of the

microrelief as hummocks generally became less pronounced. .iddiuonally. the buldozing of die

surface during fire-break construction caused 28 cm of subsidence. \ïereck (1981) aiso reponed

substantial surface subsidence following firebreak constnicùon. Ten years after the Kïckersharn

Dome G e in =Uaska. surfaces underlain by discontinuous permafrost had subsided by as much as 60

cm.

Surface subsidence on iinear disturbances:

Follouing the consuucuon of the Norman Wells pipeline. a monitoring program was

undenaken to improve impact evaluauon and rniagation Li permafrost terrain (Burgess and H q -

1989). These authon reponed pronounced aerdemenr uidun the uench dong as much as 30'0 of

the 869 km pipeline route. ;\ho. a number of small. near-circular rhermokarsr pics and ponds up to 3

85

m in diametu had developed on the pipeiine right-of-\y- (RO\V) surface. O n level suetches ot

rerrain. mench subsidence led to pondrng nithin sha1lo.t- Linear basms. while on sloping ground it

fadta ted water flow and erosion along the ditch line (Burgess and Ham- 1987). In the pipeline

uench. the rnasimum recorded sedement -3s over 50 cm at 14 of 17 sume!-ed sites. uith three of

these havuig a masimum sertlement of LOO an or more. .\long the RO\X m a s h u m setdement of

50 cm or more u-as obsen-ed at 8 sites (Burgess and Hamy 1989).

-\t the SEEDS site. seasonal subsidence races reporred b!- NoIte (1991) reached 9 cm and

12 an for the ROW' and nench respectirely. Mean total subsidence. 4 years atier ciwubance.

attained 31 cm and 58 cm for the ROW and trench respecarely fiolte 199 1).

Ground peneuating radar as a tool for geophysical investigations:

Ground penecrating radar (GPR) sun-e*g has been shown ro be a fast. reliable and

relauvely Liespensive technique for non-destructive, h@vresoluuon mapping of subsurface materiais

to depths of 3-30 m. depending upon the elecuical properties of the materials Davis and -4nnan

1989). These qualiues have esrended the use of GPR suri-eying to a nide range of disciphes. The

technique has been used in applications such as fracrure mapping @enson and ï u h r 1990):

archaeological inresugallons (Toshioh tt di 1 990) and forensic applications (Strongrnan 1993;.

In geomorphological snidies. GPR has been used in the mapping of subsurface srraygmphy

(Davis and .innan 1989. Jol and Smith 199 1. Smith and Jol 1992. LIoorrnan r / d i 1 991). I r \vas

quicl+ recognued char GPR operated opumally in mapping the s u a u p p h y and ice content of

coarse-gramed. perenniaily frozen sediments. C o a n e - p n e d deposits conraining massive ground ice

have been sun-eyed b?- DallLnore and Davis (1987. 1992). Robinson ?f di: ! 1992. 1993). B a y and

Poilard (1932) and \Y-olk & di: (1997). GPR techniques have also been used est en si^-el! to map

permafrost (.lnnan and Daris 1976. Seguin ct d 1989. Judge rt di 199 1. Pilon d d 19-1. 1993 and

acuve layer characterisucs (Pilon c./ clj. 1983. Doolirde z t d l990). Finaiir-. GPR \vas used in

geotechnical inrestqgauons of slopes along the Norman \Yeils pipeline @urges tt L 1995. Sfoorman

ef d 2995).

O b jecaves:

The objectives of this smdy were:

il El-aluate post-fie seasonal subsidence in a subarctic upland forest underlain by disconunuous

zi) Evaluate rotai surface subsidence since ROK' clearing (1986) and since the iasr topographie sume-

(1 990).

Methods:

T o ~ o m ~ h i c Sun-ec

Seasonal and longer-term subsidence was determlied by leveIing. Two sun-e?-s were

conducted in 1997. The f i t s u - e r u-as conducted 01-er a period of four dars (3-6 !une). as close to

the onser of diau. as possible. The second sun-e!- v;as carried out benveen 7-10 .\ugust. For logsacai

rasons. this sume'- was carried out before the maximum thaw depth \vas reached. -4 rotai of 1050

points were sun-eyed each cime. Points were numbered and marked with pin tlags to ficilirate the

second sun-ey. .% rotai of 43 points could not be relocated during the second sume?*. Surface

elevauon w a s measured to the nearest centimeter. using a Soidisha B2 .\utomaric level. During each

siting the bearing of each point was recorded. Elel-arions and bearings were uansferred to a p d

produang a triplet t-~:i.d of coordinates to produce contour maps and @ta1 eievauon models

iDEhls).

For both spnng and late surnmer surr-eys. dl elel-auons were measured from a pre-

established benchmark ar the SEEDS site. This benchmark was established and used as a damm in

1990 during a s d a r esercise &olte 1991). The danirn consisred of rhree u-ooden dowels placed in a

triangle, 1.5 m a p m and anchored to the permafrost Bol te 1991). -Uthough the do\\-& u-ere

p d y bumed. enough stock remained to re-establish the benchmark in 199'. Closmg errors urre

corrected accordmg to the benchmark using standard techniques. The range O P error was believed to

be u i t h 2-53 cm.

Frorn the 1050 sume: points.

575 were located in the burned forest.

339 were located on the ROT'S and adjacent RO\Y connectors

106 were located in the trenches

40 were located dong the 1975 seisrnic lùie

30 w r e iocated in the new.1~-establis hed post-iire control.

Ground Pene tra t i n ~ Radar:

A total of three GPR tnnsects were suweyed in 1997. These a-ere established in order to

adequately represenr the various SEEDS creatments (Figure +1). The GPR data were coiiecred using

a PulseEKKO IV GPR systern (manufactured by Sensors & Software Inc.) mith a M O Volt

transmitter and 100 MHz amennae. A constant antenna offset (separaaon) of 1 m was used in

conjunction with a 0.25 m step size. A stacked pulsed radar signal of 32 source excitations was used

to improve the signal-co-noise ratio (Fisher et al. 1992 a b). Signai propagation velociues were

computed from common midpoint surveys ( C m ) and were checked -+th pubtished results (Barry

and P o k d 1992, Seguin et aL 1983).

I r ROW 1

Figure 4-1: Map of SEEDS research site and Iocarion of Ground Penetrating Radar (GPR) transects. Modified from Kershaw (1 99 t ).

Data processing:

Top0g'uphi~- d m

The series of data triplets were used to produce rwo color-classed hdl-shaded digital

elevation modeIs (DEXI) of seasonal and longer-term ground subsidence. DEhls were produced

using three prograrns kom the TERki FTRL\LI canogtaphv sofru-are. The program QSCRF u-as

k t used to interpoiate and generate a grid of surface elet-arions. This yielded a gnd composed of

565 r o w and (25 columns for the longer-rem subsidence model and a grid of -35 rows and 863

columns for the seasonal subsidence model. En both cases. a grid cell size of 0.5 m was used.

Secondly. the LIGHT program was used to create a relative radiance file. consisting of a hilI shading

of each surface. Finaiiy. the output files generated in the nt-O previous steps were integrated into a

single hill-shaded. color-ciassed surface model. The color p d e t used in the classification aas del-xsed

co allow three-dimensional riewing.

Stuti~tiLiII) LIRJ!~ xi-

The K o l m o g o r o v - O normalin. test revealed that subsidence dara were nor normally

distributed. The dara were /n (nclr~trd i~g(~nrhnt) rransforrned yet the distribution remained non-

normal. Consequendy. non-parametric statisticd tests had ro be used. Cornpansons of mean

subsidence in the ueatments was et-aluated using the KusH-\Sahi; -4NOV.4 on Ranks. \Shen

significanr differences existed benveen the treatments, Paimise ~[uluple Comparisons were

performed using Dmn 5 .\Mod.

Gmmd Penc'truting hahr

GPR data have the adramage of being recorded digrtally. ailouing for a varie? of processing

techniques ro be applieà. Dara processing was performed with the p u l s e E K 0 11- sofnrare

provided by rhe system manufacturer. The three uansects were corrected for surface elel-auon

changes dong rhe sun-ey path. -\ddiuond- an SEC gain (Spreading and E s p o n e n d Cornpensauonj

and DEWOW trace corrections were appiied ro the data. The SEC gain Kas used to compensate for

the spreading losses and dissipation of energv in the subsurface. This gain had the advanrage of

preserr-ing die relative amplitude information from the refiecrors. It aiiowed for reiiable deductions

concerning the suengrh of reflectors relative to others. eren after corrections had been appiied. The

DEWVOK' trace corrections were applied in order to remove Io\v frequenq- 'TYOW' signals

superimposed on the high frequena- reflecuons. Foiiouing corrections. the data files were esported

into PCS file formats to ladrare their manipulation in dra\t&g packages. Figures 4-4 through $8

were produced by using a combinauon of the Corel Draw and ,Adobe Phoroshop s o h a r e packages.

89

GPR &a interprrtcltion tecbnique~-:

Once GPR profdes have been plorted aich the appropriate iïlrers and gwis applied results

c m be uial!ï?ed Trpically. the f i t reflecrion recek-ed in -ch uace is cded an "air ware" whch

D V ~ I S through the air benveen the vaosminer and the receir-er. Because the propagauon speed of

this fint ware remains constant throughour the sun-ey. it c m be used as a marker for the ground

surface (Wolfe et d 1997. Robinson tr UL 1993). The second signa1 received is the ground um-e.

uaveling direcrly from the transmitrer to the receh-er through the upper surface "sliin" of the

ground. The propagauon relocities rhrough the ground are h y s slower han through rhe air and

ground waves are generdy recorded uirh a shghr dela? from the am-al of the air wn-e. However.

these signals can appear as one [hiclier wave signal where relocities are hgh. The succeeding signab

on the proales are from interfaces nithin the ground and the- are recorded in order of depth

(s hdowes t F i r) .

The patterns of reflecaons on the proules provide dues as to the nature of rhe subsurface

materid. Continuous h e remrns were expected from relatk-ely smoorh. continuous interfaces

(\Volfe et d 199'. Robinson f t d 1992 19931. Laterally conunuous retlecuons generally appev hom

sediment/bedrock contacts. well-del-eloped straagraph!- and other abrupt contacts. For the SEEDS

proues. continuous reflecuons could be generated by acke-la!-eripermafrosr contacts or

ice/thawed sediment interfaces.

Chaotic (non-continuousj retlecuons ma! reAect the presence oi rhin layers OF smaii point

source reflectors of vq-ing dielecuic constants within the ground. These could include tsolated

coarse sedïments such as cobbles or small boulders ('Wolfe rt d 1997. Pilon tf di! 1992, >loomian tf

d 1991) or ice Ienses (Barn- and Poilard 1992). Find!-. some retlecnons appear as combinauons of

chaotic and serni-continuous returns and can resdt from more extensive ice lenses or sediment

bedding.

The subiecul-e nature of GPR profde interpreration dictares that some a n d a r y data sources.

wch as cores or nearb- esposures, be used. The 33 soi1 cores (Chaprer 3) were used ro rerifj- radar

profde interprerauons. Recent GPR resulrs have shown rhar certain geologic condiuons ofren !ield

predictable results. Radar propagation \-doaues are ofren high (0.09-0- 16 m ns ' ) in ice-rich

frozen materials. These higher reloaaes enable hster pulse reflecuon': nith a higher frequenq

remm signal to the receil-er. Signal attenuauon is dso Iessened in frozen marerial. resulring in deeper

penetrauon than what would be achieved in unfrozen sediment. Inversely. propagauon reiocities

decrease in fme-gmed. unfrozen marerial. This causes a pulse "drag" on the pcofïIes resulrlig in a

thicker, smeared rehector. Cenain materials are dso known to attenuate sipals more rapidly rhan

othen. For esample. penecrauon in silrs and clays mav be Limited to a Tea. merers. perhaps sLghd!-

more if the clay is Gozen (Wolfe r t di 1397). Fina$-. signal penevation and resolution d depend on

antennae frequency. Low frequenq (35, 50 MHz) antennae d o w deep signal penetration but with

poor resoluaon of subsurface details. Inrecsely, higher frequency antennae (100, 200. UX) h W )

d o w s h d o w signal penetrauon with a iugh resoluuon of subsurtace details (Davis and -\nnan 1989).

Results:

Seasonal subsidence:

CompcrrUon between ireutmentx:

Mean seasonal subsidence in the unbumed control was at least 54'0 less than all che SEEDS

treatments (Table +l). The greatest difference occurred dong the trench where subsidence was

276'. greater than in the control (Table 41) . Kmskdl-\Xallis One LVay .liUOV.I on Ranks reveaied

significant differences in the seasonal subsidence of aii trearments (Hz376.6. df.=4. P=<0.001). .U

painvise multiple comparison of the means also reveaied significant differences among all treatments

excep t the seïsmic rir. RO\X combination of treaunents (Table 1-2) (Figure +2).

-- - -

Table 4-1: Mean 199- surface subsidence for the Bumed Forest, ROÏLY', Trench, Seismîc Lme and Control rreatmenrs. Subsidence in cm.

~Trench \-S. ControI Trench vs. Bumed Forest Trench vs. ROÏLX' Trench vs. Seismic Line Seismic L m e vs. Conrrol Seismic Lme vs. Bumed Forest Seismic Lrne vs. ROW ROK' vs. Control ROB' vs. Burned Forest Bumed Forest vs. Conuol

l'es Yes Yes \-es \-es 1-e s

so Yes Yes Yes

Table 4-2: Results of Painbise lldaple Cornparison Procedure between rreaunents using Dunn 2 .Llcthudn

SeismicTJnc ROWl ROW 2 ROW 3

Figure 4-2: Colour-classed, hiil-shaded digital elevation mode1 of 1997 seasonal subsidence at SEEDS.

h k a n seasonai subsidence Li the b m e d forest was greatest in the a r a between ROWs 1-3

(Table $3). The diffuence with the lowest value was only 1.4 cm yet diis constimted a significant

diffaence (WO.001) (ïable 4-4). ROW 3 had the most subsidence of ail ROKS (16 an) this was

Zan and 0.8 c m more than ROB;; 1 and 2 respectively (Table 4 3 ) . Hoa-ever, dus ciifference axs not

significant Fable U). In the trench treatment, the most subsidence occurred dong trench 3 doseiy

toilowed by trench ? w-hich was 0.42 cm las . Trench 1 had rhe least mount of subsidence (Table + 3). These differences were statistically significant (W0.00 1) Fable M).

I~unied Forest East ~~~d f or est ROWS 1 -2 jBumed Forest ROWs 2-3

R O W 1 R O W 2 R O W 3

Trench 3 1 3 3 1 21-18 1 2.3 - 1 1-.50 3".?0

94 1-55 156

Tcench 1 Tcench 2

Table 4-3: VGlthui treatment descriptive stacisacs of 199- seasond subsidence for the Burned Forest. ROW and Trench ueatrnenrs.

59 54 8 1

Table 4-4: Results of One-U'ay ,in;zlysis of ['ariame on Ranks w i d u n tremnents.

11.96 13.2? 1 9 3

34 3 8

Total surface subsidence since 1990:

Comprln5on befween freufmenfi:

Since 1990, the R O K traunent has subsided the most (33.2 cm) foilowed bu the trench

(32.1 cm) and the burned forest (34 cm) (Table +5).

14.08 15-28 16.0':

3.4 2.6 3.4

15-38 20.'6

3.1 4.0 3.1

73.60 19.50 21 -40

2.4 2.6

6.30 '.JO &'O

20.10 2 1 .'O 3 -30

8.30 8.40 '-80

19-40 35 .'O

i 1310 14.80

Table 4-5: Mean total surface subsidence stnce the last topopphic sun-ey (1990) (Solte 1991) for the Bumed Forest, ROK and Trench trearmcnts. Subsidence in cm.

hksimurn subsidence rook place along R O K 2, dthough ROW 3 has subsided only 0.84 cm

l a s than the former (Table 4-7). ROW 1 subsided 23 cm since the lasr sun-ey.

Nithin the trench, m a - u r n subsidence occurred dong trench 2, folowed by uenches 3 and t.

Trench 3 subsided 29' O and U i O o more than uenches 3 and 1 respectively Fable 47). The rotal

subsidence along R O K 3 was the highest subsidence rate of di SEEDS ueatments.

Subsidence in the burned foresr varied benveen 20 (Burn 1-2) and 28 cm (Bum 2-3) (Table 46).

These subsidence rates are comparable to the lowest rates observed along the vench and ROW.

Table 4-6: Mean surhce subsidence since die last copopphc sw-eu (1990) (Solte 1991)

Trench 1 Trench 2 Trench 3

~ît)un each treatment type at the SEEDS sire. Subsidence in cm.

34 24.19 1 1.32 39 U.3 1 12.6 32 3 1.5' 15.23

Total surface subsidence since clearinp ( 1986):

4

The esact location of the su-ey points used in 1990 could not be found afrer the fire. Ir was

therefore impossible to assns the subsidence of the ground where readings had previously been

taken. The rotai surface subsidence since clearing (1986) was calculated by rneasuring surface

elevation using the SEEDS benchmark and adding the mean rotal subsidence in each ueaunent as

measured in 1990 (Noite 1991). The amount of subsidence since 1990 -2s measured by using the

benchmark and subtncting the 1990 mean total subsidence values in each treatment.

Mean total subsidence since dearing ans greatest along the trenches, foiiowed by the ROW

and Burned Forest treaunents. In 1997, total subsidence in the trench was 29'6 and 6S0o greater

than the ROW and Bumed Forest respective. (Table 17, Figure +3).

Table 4-7: .\lem tord surface subsidence since the 1 986 clearing of the Bumed Forest, ROK' and Trench rreatments at the SEEDS site (Sotte 1991). Subsidence in cm.

Burned Forest ROW Trench

Ground ~ e n e ~ r t i n p radar:

The proses and protile sections are presented with vertical axes showing wo-way uaVd

cine and reaecror depth. On al1 proues, the uppermost r e m represented the direct air wave widi a

constant velocity of 0.3 m ns 1. The second and sometlries disconcinuous r e m was the direct

ground wave. This r e m cine was dependent on the propagation veloaty of the upper soil huer.

Subsequent retlecton varied in =ch treaunenr and uiiii be discussed separatelu. Soil moisture cores

and hand probing along the r u - e u line were used to corroborate the GPR interpretations of

subsurface suangtaphy.

472 T.98 1 1.24 239 63.42 18.71 105 89.38 16.31

Burned f ore~+t zrrni).s=

Protiles from the burned forest were espected to show the most complete strangraphy. as

this t r amen t was the least disturbed.

Three distinct reflectors were noted in the burned forest. .iddiciondy, the ground wat-e signai \vas

the most sporadic ar these sites. On the proules. an intermittent ground wave was present

(Figure C-i). These "skips" corresponded to the locaaon of dry hummock tops. In the inten-enkg,

uater-logged depressions, the ground wave signal \vas con tinuous.

Berneen 2.5 m and 3 m depth. the suongest and most continuous reflecror \*as presenr. Ir

couid be followed uninterrupted for distances of 40-80 m. This reflector was generally conformable

with surface topography. Dry high points on the surface corresponded to rises in the proule towards

the surface (Figure -U).Below 5 - 5 5 m depth, radar signals became incoherent and were suongly

artenuated. These residuals were hard to disUnguish on the profdes.

ROW 1 ROW 2 ROW 3

Figure 4-3: Colour-classed, hiIl shaded digital elevation mode1 of total suffixe subsidence since clearing (1986) at SEEDS.

96

ROK' swevs:

The nurnber of reflections on the ROW profles varied from 2 to 3. -\long transect 3

(Figure 4-5). two d i s ~ c t reflectors urre noted. dong sith a weaker signai at a deprh of -3-3.5 m.

Disconrinuous groundwar-e reflecton were veq- suong. appearing as thick traces. The second

reflector at a depth of -h appeared prominend!- on the profiles. Its depth rarely raried b!- more

than 3-30 cm.

Signals from the rhird retlecror were much weaker rhan the retlectors abor-e. Reflecrions

were visible at depths of 3 - 5 4 m and appeared in much shoner segments than on other profles

(Figure 4 5 ) . In certain areas. the signai disappeared entirely over distances of 10-15 m (see traces

255-2625 on Figure 4 5 aj or uas esuemeiy weak (see craces 18-32 on Figure +5 b).

Trench sun-ers:

The uench prokides were characrerized b!- faim and sporadic retlecuons at depth. The initial

groundwve signal w s only visible in short segments. .\r depth. where the Y and 3" reflectors were

visible in the other ueaunents. the uench profles had u-eak to non-esisrent slgnals. This u s

partidari- sniking for the 3d reflecror on certain secaons (Figure al). .iddiaonaii- borh reflectors

somethes had a tendenq- (0 dip downw-ard in si& tashion (Figure +Tj.

Seisrnic Line and Footnaths:

Other radar signals were obtained across the seismic line adiacent to the SEEDS site and on

foothpaths on sire. These sites hnd radar remrns s d a r to the uenches and sorne portions of the

ROW. Profües across the seismic line (Figure 48) had sporadic groundu-are r e m s and a suong

signal from the lower reflecrors. Sipals from the chird reflecror were fant and sornetimes absent.

Foorpadis and other areas of warer ~ccumulation also eshibired w:eak sipals from the t h d retlecror.

Signal atrenuaaon was not as pronounced as on rhe seismic line.

Discussion:

Surface subsidence

Ser~~onui rub~i&nri.=

The grearesr seasonal subsidence w-as recorded in die uenches iollowed by the ROK' and

the burned Forest. This simation u s similar to pre-fie condiaons where masimal subsidence u-ae

dso recorded dong trenches and ROR's (Nolte 1991). The prinapal difference in 1997 a s the

arnount of subsidence which was nt-ice that of I W O values in most ueaunents.

Figure 4-7: Radar profile kom the Trench marnent Note f ossible subsidence of the ground below - 2 . h as weli as the absence of 3rd reflector in the middie of the enc ch.

This sharp inaease in subsidence was a direct result of the &e disturbance of 1995. The

greatest change occurred in the burned forest treaanent which increased by 205'0 orer 1990 values.

This was not an unespecred resulr since h s rreament was undisrurbed in 1990. The Gre disturbance

had irs ma,xkd effecr in this meamient as the surface energ. balance was disrupred and invariably led

to inaeases in thaa- depth and seasonal subsidence. Ir is not possible to assess how much subsidence

rook place between 1990 and 1995 but. assuMng it was ml. the doubllig of surface subsidence in

dvee post-he thaw seasons. is sirnilar to results reponed by Hegginbonorn (1971) and Mackay

(1971. 1995) who reponed rapid initiai increases in thawr- depth and surface lowering afrer

dis turbance.

Addiaonall-. the d d h e had an imponant effecr on pre-diswbed ueaunents. Subsidence in

the uench increased by 18O0b orer 1990 d u e s . despite the pre-esiskg disturbance affecting dus

uearment. The likely explanauon for the increase in uench subsidence is increased inpur of

melniater from the surrounding R O W and burned foresr. This w-ould inaease heat conducaon into

the sod as \tater accumuhted in the uenches (Kerfoot 1973). .Uong the ROW, post-frre seasonal

subsidence u-as also greater than in 1990 (+176O O). This increase was ro be espected as most of the

ROK- \vas disturbed to a lesser degree than the uench. The buming of the surface organics

apparently produced suffisent microclimatic modirications to significandy increase thau- dcpth.

\Sithin the ROW and uench ueaunents. the variations in seasonal subsidence \a-ere s d a r

to chose obsen-ed in 1990 ('jolte 1991). ROK' 1 and its associated uench had the least subsidence.

This ma- be paraally due ro the age of the disturbance (RO\'' 1 u-as cleared a year after RORs 2-3)

and ro the shorrer uench on ths RO\.'. In 1990. ma-ximum subsidence was alonp RO\Y 3 and the

south link This was aruibuted ro increased disturbances by 1800 passes of an aii-terrain qcle. The

obsemed 1997 subsidence values may be a residuai etiéct of dus disturbance.

Tt9fil/ ~Xb~~i&?tt'e:

The similar d u e s of rotal subsidence benveen RO\Y and uench ueatrnents suggest that both

treatments are e-shibiting sudar responses ro differenr levels of disturbance. The initiai uenchng

uas more disruprive to the permafrosr than the clearing of uees on the ROK'. f i s difference Kvas

risible eady on in the SEEDS projecr. as urnches eshibited greater thau- and subsidence than RO\Ys

@diriger 1990. Nolte 1931. Sebum 1993). In 1997. this difference abared as s d a r subsidence

le\-els were recorded at both treatments. Ic is possible that the uildfire disturbance has been more

damagmg to the R O K than the rrench. In effect, the RO\Y may have "caught-up" to the uench

disturbance level. The same mechanism ma. parriallv esplaîn the wriations \vithm the treamenrs.

Trench 2 and RO\Y 2 had the most subsidence, followved br ROW 3 and the assoâated uench.

;Uso. ROW 3 \vas reported to have been more severel!- diswbed during construction (Xolte 1991).

The initial disnubance on ROW 3 ma!- have been suffisent to supersede an!- of the h e effects.

esplammg u-hy litde less subsidence has occurred The higher rates of subsidence on ROW 3 rnay

reflect a stronger localised response to the hre. This response ma: be greater than on ROK' 3.

resulting in the highest subsidence rates.

Çround ~ e n e t r a t ï n ~ radar ~ r o Wes:

Burned-lore~t rmtment:

The discontinuous reflections nirhui the ground wal-e are die resdt of a &elecuic contrasr

berween the dry organic mat and the \verter underlying mineral horizon. The Iateral estent of the

reflecaons resulted from areas of large hummocks. elel-ated 15-20 c m abore the ground. The strong

degree of associaaon benveen rnicrotopographic high points and these s p a l s c o n h s dus

relationship. In the surrounding depressions. ponded water or sanirated organics were otien

obsen-ed during the sun-ey. Standing \vater also irnplied saturation of the underlying mineral

horizon. The relatix-e homogeneiy in moisture contents benveen organic/mineral horizons wouid

not ailou- for the GPR signal to differentiate beween the mediums. so chat it appeared as a

contkuous reflector on the proues. On the dn-er h g h points. the dielectrïc contrast would be

sufficient to generate an. a l b e i ~ weak signal. In past smdies. GPR has proren successiul in delmithg

the interface benveen peat and underlying mineral sediment. due to the ciifferences in rlectrical

properties benveen the nr-O media (Hon-ath 1998). Radar signals were suongest d e n the conuast in

dielectnc permittk-in across an interface u-as large. In mm. dielecuic pennttux-in- is p r i m a + -

conuolied b!* moisture content (Davis c./ rlj: 1977. Kong zr d 1976). Theoreticdy. variations in

moisnire content as Lou- as one to chree percent bu weight cm be decected b!- GPR (Hanninen

19921. Theimer di, 1994). From soil moiswe cores (Chapter 3). the difierence in granmetic

moisnire content benveen surface organics and rnîneral soi1 varied benveen 7-12O0, m a h g the

in terface detectabte.

The second ret-lector Kvas from a p l - e l laver present throughout the site. This grave1 was

noted by Kershau- and Evans (1987) during c o ~ g at the site in 1986. It was also obsen-ed m some

of the cores extracted in 1997 (.ippendk -1) and ma- have prevented hrther c o ~ g in man-

instances. From soi1 cores. this layes ranged in duckness from -5-12 cm and GPR profies inàicared

ir occurred in long c o n ~ u o u s layers as weli as s m d isoiated lenses. En some instances. both the

grave1 lens and the 3d reflector (permafrost table) merged and appeared as a single. large reflector.

This onl!- occurred in the bumed Forest where thaw depth had not yet progressed beyond the depth

of the grave1 lens and the permafrost table \ a s in the ricinin of this sedlnentaq- unit. The abrupt

change in grain size. and therefore dielectric characterisacs, frorn the surrounding silts accounted for

the prominence of this unit on the profiles (Barry and Poilard 1992, S e p c.t d 1989. Smith and Jol

The deepest retlector on the prohles possibly represenred an old actn-e layer created under

cooler dimatic conditions (possibly during the i-iypsithermai) or as a resdt of pre~ious disnvbances

that occurred as much as 300 years aga The depths noted on the profles conesponded

approsimately to the smtigraphic sequence derived from the soi1 cores where ice-cemented layers

were atrained at depths betu-een 1.3-1.6 rn (Chapter 2). -\dditionaii!-. acuve laver thickness as

measured by hand probuig to rehsal dong the radar L e corroborated the deprhs interpreted from

the profles. The Rank Correlation Coeffiaent, R betu-een hand probing and radar depth u-as 0.768-

=Uthough not perfect. the correiaaon was sd good and ma? have stemmed tfom obsen-aaonal

m o r s on the radar profiles as well as during field measuremenrs. -1s noted by Dootittle et d (1990)

the probing depths ma!- be the iargest sources of error as shght spatial discrepanaes benveen the

probe site and the radar crack may have acted CO lower correiaaon. \-ariaaons in the combined

thickness of the organic mat and the acuve laver as great as 15 cm uithin a 30 cm radius of an

obsen-ation site w-ere obsen-ed. Kith such 1 - ~ a u o n s 01-er smaU distances. it is unlikely that an!-

method of measurernent could produce identicai results. The comeness of the vertical asis and the

width of the radar uace ma' have dao been poteritid sources of errors when readings were taken.

The undulating and conformable nature of the retlector in relation to the surface \vas hrthet

eridence for it being the top of the permafrost table. Brown (1967) reported chat the surface of the

frozen layer varies wirh the rnicrotopography of the soi1 surface.

The strong groundwave remrns suggested thicker and dryer organic accurnulauons at the

surface. It was therefore possible rhat drainage u-as better or char pre-tire organic thickness \vas

greater in these areas. Organic mat thickness may also retlect burn ses-erin- at these sires. with greater

accumulaaons remainuig in the less sererely burned areas. The constant depth of the second

reflector and irs s d a r appearance on the profiles indicated [fus \vas the grave1 lens obsemed on the

burned forest proiïiles. The generally fauit signal recek-ed from the third reflector was indicative OF

the degree of disturbance on the ROWs. -4ssuming this reflector was the bottom of the acuve layer.

the faint signal suggested that ice content at this interface had decreased, resdring in a weaker rerurn

of the radar signal. -Uso. GPR profrles indicated an increase in the than- depth beyond the values

recorded by hand-probing (Chapter 3). In 1997. mean thaw depth dong the ROKs was 136.4 cm

(Chapter 3). a deprh xvhich corresponded approsimately ro the depth of the second retlector (grave1

lens). Suice the probing method used probe rehsal as an indication of the masimum thaw depth. it

was possible that hand-probing grossly underestlnated thau- depth. Maay cimes dunng probing. the

probe could not be pushed hinher than 200-230 cm depth because of the c o n h g pressures from

che surroundmg thaa-ed SOL Similady. the probe aras exuemely hard to extract when it was pushed

beyond -2.5 m depth.

Tm%, J u n T

The weak signd r e m kom

and sanuauon of the sparse organic

the first uench reilector resdted from hgh moisture contents

cover. Throughout the SEEDS sire. che mach consütuted a

shailow depression 20-30 c m Iower than the surrounding ROK.. This created preierenual ciramage

touards the trench. keeping the moisnue content high. .4dditionallr. dueng conscniction of the

SEEDS site. surface organics were remored with escaration and mised-in during backtilling

(Kershau 1986). .Uthough some orgdnc marerial has groun back since the fue. the orgamc mat

found elsewhere at SEEDS mas generally absent hom the uench. These condiaons esplained the

iack of sporadic ground\vave syials that u-ere obsen-ed in the burned forest and RO\Y rreaments.

Subsequent faint signals from the deeper retlectors result from the hq$~ degree of

disturbance during site construction. The uenching and back-t&g disturbed and mncated

sediment layers to a depth of 50 cm. .iddiùonaIly. uenches eïhibited the deepest thaw depths and

these thick thawed sedunents attenuated radar signais resulting m fatnt renirns.

Benveen traces 81.5 and 83.3 (Figure 46). the third reflector u-as discontinuous and dtpped

dou-nuard. The nvo reflectors abo\-e it were also mncated and displaced. These signais were the

result of surface subsidence that may hare modified the posiuon of the grai-el lens foUowing the

locnlized deepening of the active layer. .\long the other uansect. radar signals were suggestive of

significant deepening of the acuve layer (Figure 47). O n these profiles. the water-sanuated silrs

suongly attenuaced signal penetrauon, resulting in chaotic mces that did not peneuate belou- 2 - 5 3

m. This n-pe of signal renun has been r e c o p e d as typical of a thawed. fine-grained active layer

(Segum et rii. 1989, Pilon et 6 1 992, Doolitde ef ai. l99O).

.$ez~-mz~. h e andfoopa~h~- J-MKYJX:

ïhe signals from the diLd reflector dong the seisrnic line were faint and sometimes absent.

suggesüng an overdeepened active layer over these areas. Foochpaths and other areas of water

accumuiation also had weak signals from the thLd reflector. Signal attenuauon was howvever not as

strong as on the seisrnic h e . The main effect of ponded water on signal returns seemed to be n

complete artenuation of the groundwave. followed by chaotic renuns doun the trace. Subsidence did

not seem as deep as in the uench since intemal straugraphv wxs not disnirbed.. Thrs was not

une-xpected when considering the ciifference in the degree of disturbance of these twn sites. XIost

changes created by ponded water sternmed I-iom its hgher heat capaary which increased soi1

temperatures (Kerfoot 1973). In conmst. the uench and seismic Iines were hem-h- disturbed . u-ith

surface organics k i n g serereiy crampled and/or completely remot-ed. thereby modih-ing the energy

baiance at the surface.

Interes~gly, the cornparison of radar protiles berneen the trenches and the seismic h e can

possibly give information on the recoven. tirne of such &turbances. It uas apparent that --en 23

years after iniaal disnirbance, the permafrost beneath the seismic line had not recovered to its pre-

disnirbance conditions. The dqxh of the amive la-r had increased and it did not seem to be

aggradtng. as illustrated by the absence of an ice-rich layer a t the freezing front. This funher

suggested that permafrost below the uench could still be degrading for at least 10 years. despite

ongoing plant recel-en (assumïng constant ciimatic conditions).

Conclusion:

Three thaw seasons after fie. there were significant difkrences in the mean seasonal

subsidence of ail SEEDS treaunents. XIean subsidence was h h e s t in the uench and the ROK'

ueaunents. The burned forest had onlv subsided 2 cm and 6 cm Iess than the RO\X and uench

respecavely. This situaaon was sirnilar to pre-tire conditions where rnasimum subsidence occurred in

the trench. RO\X and burned foresr. In 1997. the principal difference \vas the arnount of subsidence

which wxs double the pre-Cire values for most ueatments. This increase \vas a direct result of the

surface disturbance by tire. The burned forest had the strongest response to the wddfrre as the

increase in thaw depth utis 305" o greater than the 1990 pre-Cie \dues. Tite rapid intual response of

dus ueamient \vas due to the tact that the burned forest was undisrurbed (unlike the ROW and

trench) before the fie- -4ddiuonall!-. the uildfue had an important impacr on pre-disturbed

ueaunents as both ROW and trench eshibited significant increases in subsidence.

Total subsidence since clearing was htghest in the trench and ROW. The burned forest had

the smallest change. f i s was due ro nvo factors: the tirne since disturbance and the severin- of the

disturbance- The trench u.as the mosc disnirbed treaunent and it had the greatest surface subsidence.

Inversely. the burned forest \vas moderarelr ciisrurbed bv wildfïïe and had the least subsidence.

Ground penetrating radar proved to be usehl for accive layer invesagauons. .At least 3

reflectors were risible on radar protiles from the burned forest. In the other nvo rreaunents. 2-3

rekctors were risible but the quality of their signal was 1-ariable. Signal attenuation \vas suongest in

the most disnirbed ueaunents (trench and ROW) where a thck acrive ial-er decreased signal

penetraaon. The interfaces benveen thawed and frozen material were strong c o n ~ u o u s reflecrors.

These signals perrnitted the detecaon of lavers of coarse mineral matenai. Finally. because of the

htgh dielectric contrast berween thau-ed and frozen material the bottom of the active la~er w t s

visible as a strong concinuous reflector. The atm-e layer depths inferred from the GPR protiles

sornetirnes exceeded values obtained b~ hand-probing. This was particularly m e in areas where

thawed sediments could not be entirel- peneuated. This impiies that hand-probing ma2 have

underestima ted maximum thaw depth, panicularly a fter 1 99 1 - 1 992 when the deeper thaw dep ths

made probing more difficult.

Annan A.P. and Davis J.L. (1976); Impulse radar soundmg in permafrost, R&o SLlzm. 1 I.(4).

p.383-334.

Barry P.J. and Pollard W.H. (1992); Ground probing radar in\-esqations of ground ice on the

Fosheim Peninsda. Ellesmere Island. Northu-est Temtories. .\lzt~-k-Os. 39, p.59-66:

Benson RC., Yuhr L.M. (1990); Eraiuaaon of fracrues tn siIts and da!- usmg ground penetraring

radar, In: Lucius, J.E.. Ohoefi. G.R and Duke S.K. (eds.). Tbird I~nrrlrionrli Coqewnce on

Gru~tnd Penttmting bah? Denver. Colorado. United Scares Geologïcal Sun-ey, Open File

Report. 1 1. 39 p.

Brown J. (1967): Tundra soils formed over ice u-edges. Sonhern -Maska. Sod S&mr Sot7tg. of'--1menh

Pmceeding. 31. p. 686-691.

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p.33-9U.

Burgess M.M., Robinson S.D., Moomian B.J., Judge AS. and Fridel T.W. (1993); The

application of ground penetraring radar to geocechnica1 invesugauons of insulated

pemafrosr dopes dong che 'iorman KeUs pipeline. Somvest Terntones, l ' m a n / i r ~ n ~ ~

Pmceedng. 4 8 ~ Cun~dirln Geote)c-bni~'rlf Co@nie. \'ancouver. B.C.. p. 999- 1 OO6.

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Sun-er of Canada Paper 87- 1-1, p.9 13-9 18.

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ice, In: Gmitnd penetruting ruAr, Pilon J..i. (Ed.), Geologtcal Sun-e!- o i Canada Paper 90-4.

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Davis J.L. , h a n AP. (1989); Ground penetrating radar for hgh-resoluuon mapping of soi1 and

rock stIat@aphy, Geopb~-i~uf pm~~Liin& 37, p.53 1 -55 1.

Davis J.L, Topp G.C., Annm A.P. (1977); Measuring soi1 =ter contenc in-situ using tirne domain

reflecxornerq- techniques, In: &pot of-a~~it i t ie~-. Pat B. Geoiogi~izi Snnq q-Cuncfuh P*prr ' T - l B.

p.33-36.

Doolitle JA, Hardis@ M A . and Gross M.F. (1990); ,+ ground p e n e m h g radar stud!- of acuve

laver ducknesses in areas of moist sedge and wet sedge rundra near Bechet -ilaska. US-\,

.-Inh- mui.-ilpine &J-erlnh, 2 (3). p.175-183.

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ground penetrating radar data, Geopt!yzt~, 57, p.49 5-504.

Fisher E., McMechan GA., Aman A.P., Cosway S.W. (1992 b): EsampIes of rel-erse-tirne

migrauon of single-channel ground penetrating radar profides, G t ~ p & i ~ . 57, p.377-586.

French H.M. (1976); The Periglacial Envuonment. Lonpan , London and New-York 309 p.

Hanninen P. (1972); -~pplication of ground peneuacing radar techniques ro peatland investigations,

In: Hanninen P. and ,brio S. (eds.). F O U ~ I Intemrl~iond C#+Wit'e on gmztnd p~netr~1in3 rrlhr,

Rovaniemi, Finland, Geologcai Sun-ey of Finland, Special paper 16. p.2 17-22 1.

Hegginbottom J.A. (1971): Some effects of a forest tue on the permafrost active laver ar Inuvik,

!KU?. In: Ptoceedings U\'J Seminclr on fbe Penn@~-t .-it-tzzr L ~ r r . Xationai Research Cound of

Canada, -4ssociate Committee on Geotechnical Research, Ottawa, Technical Xiemorandum

NO. 103. p.3 1-36.

Horvath CL. (1798); -ln evaiuation of ground peneuating radar for investigations of pdsa

evolution, XlacmiUan Pass, Nonhwest Temirories, NSc. Thesis. Department of Earth and

-4uriospherï~ Saences. C'niversin. of .ilberta, Edmonton, ,ilberta. 207 p.

Jol H.M. and Smith D.G. (1991); Ground peneuating radar of northern lacustrine deltas. Chdditzn

]oz(rnd of'Em'h !Litnies, 28, p. 1 939- 1 947.

110

Judge AS., Tucker CM., Pilon JA. and Moorman B.J. (1991): Remote sensing of permafrost by

ground penetratïng radar at nvo aitports in -ircac Canada,.-ln?L; 4-4, Supp. 1. p.-Ki48.

Kershaw, G.P. (1988); The use of conuoiled surface disturbance in the testing of reclarnation

treaunents in the Subarcuc, In: Sorthem Em7ronmentJr' D i ~ ~ t ~ & ï n i i ~ , Kershau- G.P. (Ed.), The

Boreal Insatute for Northem Studies, Occasional Publication So . 34. Edmonton. p.59-70.

Kershaw, G.P. & Evans, KE. (1987); Soi1 and near-surface permafrost characteristics in a

decaden t black spruce stand near Fort-Norman, NKT. B.c GtogrihiLirl Sené,; Sio. U. p. 15 1 -

166.

Mackay, J.R. (1 993); -4ctk-e Layer Changes (1 968- 1993 follo\wlg the foresr-tundra fue near

Inux-k N.\V'.T.. Canada. :lrc./iL- und :!@nt fherlfih, i.01.27. -\;o.-!, p. 323-336.

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-Arctic. CrlnJdrjn G t o r e o . i'01.7, p. 237-249.

Moorman B.J., Judge A.S., Burgess M.M. and Fridel T.W. (1995); Geotechnical in\-escigauons

of irisuhted permafrost dopes along the ';orman \Kells pipeline using ground p e n e t r a ~ g

radar. Pmiecai'ngj. VI' Intrmcltionrli C O & ~ ~ P OII Gmmd Penetrrltins R&K U'aterloo. Ontario,

\'01.2. p.47'-49 1.

Moorman B.J., Judge A.S. and Smith D.G. (1991); Esamtning Burial sediments using ground

p e n e u î ~ g radar in British Columbia, In: Cmnr R~J-eun-h Pmt .-1. Geologlcal S w e y OC

Canada, Paper 91 - Li, p.3 1-36.

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Characre~stics (S EEDS. NKT. Canada). Diplomarbeit am Fachberuch Geographie der

Phillips-Cnil-ersita~ hIarburg/L.ahn. 167 p.

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permafrost and subsurface characreristics of surtiàal deposits in Iiangiqsualuijuq, northem

Quebec. In: Gmmdpenetmting ruAr, Pilon J-A. (ed.). Geological Sun-ey of Canada Paper 90-4.

p. 165-175.

Pilon J A , Annan A.P. and Davis J.L. (1985); Monitoring permafrost ground conditions ulth

ground probïng radar. In: Brown, J.. Xlea. 1LC. and Hoeksrra. P. feds.). Ir'orkbop on

Penncft;o~-t G c o p ~ ~ i k . Golden, Colorado. CSCRREL S p e d Reporr 85-5. p.71-'3.

Pilon J A , Annan A.P., Davis J.L. and Gray J.T. (1979): Cornparison OF thermal and radar acnl-e

layer measurement in the Leal Bay area. Nouveau-Québec. Gtogrqhie PLyiqru tt Q~~~tt'rnrlin.

33 (3-4). p.3 17-336.

Robinson S.D., Moorman B.J., Judge AS., Dallimore S.R. and Shimeld J.W. (1992); The

application oi radar svatigmphic cechniques to the investigation of massive ground ice ar

Yaya Lake. Northu-est Temtories. .\,l~t~-k-Os. 39. p.39-49.

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massive ground ice at Yaya Lake. Northwest Terrirorie': using radar straugraphy techniques.

In: Citmrr? fheufr'h krr B. Geological Sun-ey o f Canada. Paper 93- 1 B. p.23-32.

Seburn D.C.il993j: Ecological Effecrs oi a Cnide Oil Spa on a Subarctic Right-of-N-ay. MSc.

thesis. Department of Geography. 'niversin of -Ubena. Edmonton. 145 p.

Séguin M.& Aliard M., Pilon J., Lévesque R. and Fomer R (1989): Geophysical detecuon and

characterization of ground ice in northern Québec, In: I ' q m witb --lh-trt,u. Groio_?ilil!

lrrot-ljrion of CianrldLr, 14. -\76.

Smith D.G. and Jol H.M. (1997): Ground penecraung radar in\-esagaaon of a Lake Bonnede

delta. Provo leveL Brigharn City. Ctah, Gtoiog, 30, p.1083-1086.

S u o n p a n ILB. (1997); Forensic applications of ground penetraûng radar. In; Gmund penetrrltin~

ruAr. Pilon J.-\. (ed.), Geological Sume!- of Canada Paper 90-4. p.203-313.

Swansoii D.K. (1996): Susceptibiiity of soiis to deep diau- foiiouing forest fins Li interior .ilaslia,

CS-+. and some ecologic implicaaons. --in-~ii.-crnd :IICpine R~JcuR'~, 18.217-227

Theimer B.D., Nobes D.C. Wanier B.G. (1994); -+ sud!- of the geoeleftrical propenies of

paciands and their influence on ground penetrating radar sun-e+g, GmpoiiiL~fi Pm.tper.ting.

42, p. 179-303.

Toshioka T., Osada M., Sakayama T, (1990): -ippiication of p u n d penetrating radar to

archaeologÎcai inrestigations. In: Lucius, J.E., Olhoeft. G.R. and Duke S.IL (eds-j. Tbird

Internrl~iond Coq+Zmnce on Gni~tnd Penetrrring Ruhr, Denver. Colorado, cnired States Geologicai

Sun-ey, Open File Repon. 1 1.

Viereck L A (1989); Effecrs of Cie and tkelines on acüve la'-er thckness and soil temperatures in

interior ,-Uaska, In: Perm&~-f- Eourlh Crtn~fakn Conr2~nt-e Pmmding~-.

Xlarch 2-6. 198 1 .Calgan-. .-Uberta, National Research C o u n d of Canada, -Associate

Committee on Geotechrilcal Research. Ottawa. p. 123- 135.

Williams, P.J. (1983); The Surface of the Earth: -An Introduction ro Geotechnical Science.

Longman. London and New-York 312 p.

Williams PJ. and Smith M.W. (1989); The Frozen E h . Fundarnentals of G e o q o l o g .

Cambridge: Cambridge Coi\-enin- Press. 306 p.

Wolfe SA., Burgess M.M., Douma M., Hyde C. and Robinson S. (1993; Geological and

geophysicai inresugations of masske gruund ice in glaciot7uvial deposirs. Slave G e o l o g d

Province. biorthwesr Territorles. Geohgird J ~ t n f n q -C~nr l& Open File R r p o ~ 3442. 3) p.

Wong J., Rossiter J.R., Oihoefr G.R. and Strangway D.W. (137); Pemiafrosr: elecaical

properties of the active layer measured h ~itz,., C u n d u n Jo~trnui O/ Euril, lie nie^-. 14. p.583-586

Chapter 5: Conclusions

Wï.ldGes modifj- permafrost-affecred soiis by changïng the e n e w balance at the ground

surface (Broan 1983). This usudy lads to an increase in soil temperatures and the melang of

ground ice. resulring in a thickening of the acol-e-ber. Geomorphic repercussions of ground-ice

m e l ~ g include surface subsidence because of the rolume loss associated uïth dus phase change.

,idditionallv, the drainage of melwater Ieads to second? subsidence as pore space decreases.

This thesis has esarnined the microchatic and geomorphic responses of a Subarcuc upland

fomt underlain by permafrosr in the thrd thaw rasons follouuig uildfue.

.~[iLmt-/inatiL' ??JQO~J-&- /O wddtire:

The buming of the SEEDS site has lead to substanriai moditcaaons in the energ- budget of

the surface. The burned ueaunents recel-ed Ievels of shon-wave radiation chat were 21 -50" O greater

than the conuol ueaunent. Outgoing short-u*ave radiaaon was lou-er in the bumed ueaments bv

1+30° O. This resuited t'rom the sudden darkening of the organic layer foiiowing burning. The darker

surface led to a decrease in surface albedo. This. in nini, fawred greater absorption of solar

radiation and inaeased soi1 iernperarures in die burned treaunents.

Incornhg long-wave radiation uas also greater in the bumed ueaunents than in the conuol.

This occurred as a result of cree canopy rernoval whch dou-ed the penemuon of HI- ( 9 O O more

radiaaon. The warmer soi1 temperatures in the burned ueaunenrs led to higher amounrs of outgoing

long-wave radiation over these surfaces.

The remoral of rhe vegetauon canopy also led ro a decrease in relative hurmdrty and a n

increase in uind speeds over the burned ueaunents. .iir temperatures ar 1 3 cm heighr were cooler

in rhe burned ueaunents because ofgreater hear advecaon.

Burning also altered snowpack characrenstics. The SEEDS treatments had r h n e r and

denser snoupacks than d&g pre-he conditions. This \vas again due to regetarion remoral wvhrch

favored snou- redistribuaon and wïnd acuon. -\ Heur Trmg'èr CotjiLIent (HTC) (Kershaw 1991) was

calculared to assess the porenaal for hear ioss from the soil. High HTC values were iound in the

burned forest and on some ROW sites, suggesting that these sites u-ould be poorly msuiated and

would aiiow greater frost peneuation.

Soi/ rnoi~fztn und u&e f q e t dgpth r n o ~ i c r i o n s jollo Mirg wiidtie.

Burning led to a decrease in soil moisrure contenr as a result of ground-ice melting and

melnvater drainage. The greatesr decrease occurred in the upper 15-Xcrn of the soil column as the

114

surface orgvuc laver uas drier and dunner thui in the conuol treaunent. The lou-er post-Gre albedo

of rhe organic laver and die increase in surface temperanues favored greater rates of evaporaaon

and, hence drier conditions. Belou- 20- moisme content was again lower than in pre-fire

conditions. Howa-er, the ciifferences bent-een ueaanenrs were more variable and dus \vas thought to

be a h c t i o n of the age and severity of the disturbance. The uench, the most sererelr disrurbed

ueaunenr, had low moisture contents at depths greater than a l i other treaments. This likelv resulted

from the h e since ground-tce thawing had begun. ailouing for krge arnounts of melnuater to drain

am!-. The ROK- aiso had lowered moisme contenrs. alrhough not as deepl- as the uench. Finaii!;

the burned forest had the least amount of change in soi1 moisnue content, presumably since h s u-as

the least disturbed ueaunent and the time since disnirbance is still short.

The a&ve layer response to the nddfirt \vas variable throughout the SEEDS treatments.

The uench treaaent had the Ieast amount of post-he active laver increase, foilowed bv the ROW

and the burned forest ueaunents. The uench sites were Little affecred b!- the uildiïre as thaw depths

uTere not s~gnificand!- different from the last pre-tire measurernents and the 1996 values (Kolte 1991,

Nolte and Kershaw 1998. Seburn 1993. Seburn and Kershan- 1997). The majonry of the increase in

active larer depths in the RO\Y and trench treaments were a result of the initiai dismrbance and

k e l - occurred benveen 1986 and 1995. This lou- increase kely rtemmed from che degree of

disturbance of the initial clearing of the RO\Ys, chat superseded the microclirnauc modifications

caused br wildfire. The burned forest sites e-dubired signitcanr increases in thaw depchs. This \vas a

result of the modifcaaon of the surface enerE balance resulting from the burning of the organic

mat and the remord of the uee canopy. allouing thaw to progress deeper into die ground.

Thennokxn-t und J - I I ~ U ~ . P b~-idem ~/o/iuWing zviidfire:

Posr-tire seasonai subsidence was highest in the uench. foliowed b - the RO\Y and burned

forest This pattern was s i d a r to pre-he conditions F o l t e 1991). The phcipal difierence was the

amount of seasonal subsidence whch \vas aimosr doubled in 1997 compared to the pre-Fie \-dues.

This increase was a direct result of the surface dismrbance int-licted by the wildfire. The burned

forest had the suongesr response to the wiidfxe as the increase in thaw deprh uas 20j0 O greater than

the 1990 pre-he values (Xolte 1991). The rapid initial response of ths treaunent \vas due to the tact

that the burned foresr \vas undisturbed (unWie the R 0 W and crench) before the €ire. .+ddinonaiiy.

the d d f i r e had an important impact on pre-disturbed treaunena as both RO\X and uench had

significant increases in thau- depth.

Total subsidence since ctearing uTas highest in the trmch and ROI\'. The burned foresr had

the smallesr increase. This was again due to the Ume since drsmrbance and the severip- of the

II5

disturbance. The nench was the most disturbed ueaanent and it had the largest increase in total

surface subsidence since clearing. Invers* the burned forest was moderately disnirbed br d d & e

and it had che least subsidence.

Ground penetrating radar proved to be a ver)- usefbi tooi for actire larer investigations. -At

Ias t 3 reflectors were msible on radar profiles Gom the burned foresr. In the other m o ueaments,

2-3 retlectors were risible but the qualin. of th& stgnal was t-ariable. Signal attenuaaon was snongest

in the mosr disturbed ueatmenrs (trench and RO%] where a thick active b e r decreased signal

penetration. The interfaces benceen thawed and frozen material produced suong continuous

reflectors. These signais permitred the detecrion of iayers of coarse minerd m a t e d Findy. because

of the high dielecuic conuast benveen thawed and frozen materid the bottom of the aca\-e i a o

was visible as a sa-ong continuous reflecror. The acnt-e layer depths inferred from the GPR profiles

sometimes exceeded values obtained by hand-probing. This was pamcularly m e in areas where

thawed s e h m t s prevented the penetraaon of the probe. This irnplies that hand-probing may have

underesrimated m a - h u m &au- depth. particulady afrer 199 1 - 1 992 when the deeper thaw deprhs

made probing more difficuit.

Three thaw seasons afrer he. there were significant ciifferences in the mean seasonal

subsidence of aii SEEDS treaunents. Sfean subsidence u-as highesr in the trench and the ROK'

ueaunents. The burned forest only subsided 1.7 cm and 6.3 cm les5 than the ROK and uench

respectively. This situation was sirnilas to pre-fire conditions a-here masimum subsidence occurred in

the crench, ROW and burned forest. in 1997, the principal difference was the amounr of subsidence

whch was doubIe the pre-t'rre raIues for most ueaunents. This increase was a direct result of the

surface disturbance caused by the ddfue . The burned forest was most alcered b!- the d d f u e as the

increase in thaw depth was 20j0 O greater rhan the 1990 pre-€ire values. The rapid initial mponse of

h s treaunent was due to the tact that the burned foresr was undisturbed (unlilie the ROW and

uench) before the hre. .iddiuonaii~, the wldt ie had an important impact on pre-disnirbed

ueaments as both ROW and trench had significant increases in thaw depth.

Total subsidence since clearing \vas highest in the uench and ROW. The bumed forest had

the smaliest increase . This was due to w o factors: the time since disturbance and the sewxïn- of the

disrubance. The uench was the most disturbed ueaunent and it had the largest increase in surface

subsidence. Inverseiy, the burned forest was moderately disnirbed by d d t i r e and it had the least

su bsidence.

Future avenues of tesearch:

This sntdv w a s an esunination of the miaodimate and geomorphic responses of a subarctic upland

forest, three thaw seasons after d d f ~ e . ,ilthough this stud- is over. the resulrs reported herein are

limired by the short tirne span over which it was conducred The microchmate and geomorphic

changes obsen-ed in 1997 con&ue to respond to the initial disturbance and uill so For the forseable

funire. Therefore. the results of ths smdy provide a basis for cornparison for hue work on the

site. The SEEDS site is unique in chat it dous a v e - detailed analysis of micro- and meso-scale

processes o c d g over a smail geographical area. These conditions udl dou- m o n i t o ~ g of the

long-term post-&e response of discontinuous permafrost in a detail of spaaal and remporai scales

that has never been reported In this h g h ~ 1 have listed possible arenues of f i d e r research:

- Throughout h s thesis. the transfer of heat into the sod was invoked many &es to esplain

increases in acuve layer depth and surface subsidence. CnfomnateI!-. the importance of this

parameter remained purel!- speculation as no data u-ere collected to suppon such statements.

Therefore. hm efforts should be made to quanti- soil heat flus as u-el1 as the soil characteristics

that influence themal conductivin- (narnelv porosip-. ice/u-ater content. bulk densin-).

- In the same hght. a berrer sysrem of soi1 temperature measurements should be used. The curent

set-up does not allow for accurate measurement of soi1 remperanues below I W cm depth as

thermocouples are unerenly spaced. -4 better system could employ a series of thermocouples. e\-enI!-

spaced at 5 or 10 cm. This therrnocouple string could be mchored in the permafrost as deeply as

possible (possibly 3-4 m depth). Such a serup would ailow for \-en prease temperature

measurements with depth and the possibility to locate the bottom of the acal-e layer mith the O°C

kotherm. Combining these temperame measurements with better characrerizauon of sod conditions

would permit req- d e d e d analysis of active iayer development and the seasonal/annual fluctuaaons

of the active layes. This witi be increasingly Unponant if the active layer increases beyond depths

where the probing method can be used. Finally. usuig this semp would gn-e information on the

maximum thaw deprh and the freeze-back process. Borh need ro be measured and quanuhed at

SEEDS.

- Increases in surface subsidence and thaw depth should be monitored dosel!-. espeuauy in the

bumed forest as rhis site d l respond to the uildfire disrurbance orer the nest feu. 1-ears.

=\ddicionaily, thaw depth and subsidence should be rnonitored in the ROK' and trench treatmenrs ro

assess the importance of the 6re disturbance on the pre-disrurbed treatments. Ir is of interest to

know if these treaments continue to respond strongly ro the fire disnubance or if the iniaai dearing

disturbance is overriding the fke dis turbance,

- Finail., the extensive pre- and posr-fîre database wouid be particuiarly weii suited ro the

development of a compurer modeL .idcihg data on soil temperarures and moisrure could aiioui the

derelopmenr of a coupled atrnosphere-permafrost model. If a suirable mode1 u-as dedopeci.

prediaions of permafrosr response could be made under nr ious conditions. This could indude

dlnauc aamilig or c o o h g and rhe effecrs of repeared disnirbances (successîve uildfires oc&g

over a shorc tüne span).

References:

Brown, RJ.E. (1983); Effects of G e on the ground themai regime. In: The Rok of Fie in

Northem Circurn~olar Ecosysterns, RW-YCéin and D..-\. XhcLean (eds.). Scope 18. John

K'yIey and Sons, 322 p.

Kershaw G.P. (1331), The influence of a simulated nanspon corridor on snowpack characteristics.

Fort Norman, .u'.K'.T., Canada -4n-t~~- und .-l@ne Rrseunh, t'01.23. No. 1 p.3 1 - I O .

Nolte S. (1991); Some Geoecological Effects of Disturbances on Near-Surface Permafrost

Characterisucs (SEEDS. WST. Canada). D i p l o ~ b a r am Fachbereich Geographie der

Phillips-Cnkersitat. Xlarburg/Lahn, 167 p.

NoIte S. and Kershaw G.P. (1998); Thau- depth characteristics orer îïve than- seasoas follouing

installation of a simulared vanspon comdor. Tulira. hXT. Canada. PrmutrO~-t andpmgirlLid

prn~m-e~- . 1'01.9, p. 00-00.

Sebum D.C.(1993): Ecological Effects of a Cnide Oil Spill on a Subarctic Right-of-Ka!-. 'iI.Sc.

thesis, Department ofGeopph\-. L-niversiy of .ilberta, Edmonton. 145 p.

Sebum, D.C. and Kershaw G.P. !1993: Changes in the actil-e layer of a subarctic righr-of-wa!- as a

resdt of a crude-oil sp~ll. Cmudicrn J o m w f af-&flb Litm. Xo.34. p. 1539- 15-44.

o m m m e c m F Z - - ~ < ( N ~ J s m e . A a - 8l)r m * t ~ ~ ~ & ltAoioio

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