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JenniferE.Tollefsonl,Departmentf Botany, niversy of VermontBur ngton Vermont 5405

Ffederick . Swanson,USDAForest ervice. ac c North\ lest esearch tat n 3200JeffersonWa v Corva sOregof9733l

an o

John H. Cissel,Bureau f Land 4anagement OBox 10226, ugene. regon 7440

FireSeverity n Intermittent treamDrainages, esternCascadeRange,Oregon

Abstract

We quantiiicd irc severil\ prtterns$'irhin ntermittcnlstrexmdrainagesn a recenrlybumcd,lrca of the cenral wencm Cascades.Ofegon.Aerial pholographsr ere used o estimate osl lrc live canopvcover vithin slrcamside nd uplandzoneson rhc soude.rstand south$e\I-facing slopcs of 33 \iatersheds.Live canopy colcr did not differ sigrrificanlh bclween streamside nd uplandzones n the $aiersheds.Firc sc\crily dala obtained rom aerialpholographswere highl,vcorrelatcd$ith lire severirydata oburined n the field in \ix of thc qalcrsheds.confirning that aerial pholognph esiimrte\ of live canopy cover reflecred acrualcondilions on the ground.whilc prclious studies ndicate hat firc sc\crirv ma) be lo\\'er alongpercnnialsre.rnN. he fesultsofthi\ \tud)_suggest hat ilrc scvcritv n inknse event\ may be similar bet$een intermittent strea channelsand adj.rcent plandareas.At the hndscapc scalc.dilGrences n fife se|eritl along slreamsof different sizesnray nilucnce rhe mo\aic of post firc

vegetation nd contribulc o o!crrll nructural di|eNity in forcns of mouDrainousandscapes. irc rcgime rfbrmation obtaincd l1tiis and felated tudies nraybc used o guide fore\t managenrcnl cliliries that are modeledaftcr natural disturbance roccsscsand seek o balancecomnrodilyproductionand ecoslsten protection.

Introduction

Contemporaryecologistsagree h t natural dislurbancc vents ccurringovervariousspatial ndtemporal scalesarc ntegralcomponents f eco-slslems White I979, Pickeuand White 1985.Sprugel 991,Whiteet l. 1999).nfbnnation boutthe histoic l'rcqucncy.sevedty,and spatial cx-tcntof suchdisturbance lents can be applied olandscapcmanagementAgee 993. Huntcr 1993.

Morganet al. 1994,Swanson t al. 1994.Engstromel al. 1999).Basedon the assumptionhat spe-cies have adapted o a certain range of ecosys-tem conditions reated y naturaldisturbanceregimes.he concept f managing n ecosystemrvithin ts rangeof naturalvadability s beingerplored as a way to increase he potential forsuslaining ative pecies cross broad ange fhabitat ypes Morgan t al. 1994.Swanson t al .199.1, ngstrom t al. 1999).

ln thc Pacitic Northwest, ederal orest man-a-qcnent bjectives nclude both ecosystem ro

rAuthor to who r corcspondence hould be addrc\scd.

E mail: tollefson@hard.cdu.Cunent address: udronia t-ld.

PO 8or 5000, Annandale. !'u YoR 1250,1

18 6 Northwest cience. ol.711. o. 3,2004

e . ]1 ) r i l l i ) r l , c \ ra h re !5 f ie n ! i .A * o . j r rd j , \ l l r i g h n rc \ rn e d

tection and timber production. Thc Norlhu'estForestPlan employs a systemof static reserves.corridors,and habitatmanagement rescriptionsfor matrix lands o protectan array of terrestrialspecieshought o dependupon atesuccessionalforest habitat, o protectaquaticecosystems.ndto provide sustainableupplv ft imber(USDAand USDI 1994).Riparian eserves. hich con-sist of zonesof uncut orest along streamsof allsizes.arean ntegralcomponent fthc Nofthwest

ForestPIan. These cserves.which are ntcndedto prolcct streamsldeareas,concentrate lmbermanagementn the uplandareas etweenbuf'fersand esult n spatialsegregation fold andyounglbrest stands.

An altemativestrategy br meeling he broadobjectivesof the Northwest ForestPlan nvolvesus ing a tura l i s tu rbrnceeg imen lonnr t ion , . rguide orest management ctivities Cisselet al.1999). n Douglas-fir .P eutlotsuga enli e i )dominatcd brestsofthe centralwcstgrnCascadesof Oregon, ire has historically been the dominant naturaldisturbance gcntand a pdmary dc-terminant fforeststmcture ndcompositionAgee1993. Weisberg1998. Weisberg1ir Prcss).Un-derstandinghe angeofnatural variabilitv within

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this andscapc,herelore.s coutingeirt pon antundcr . tand in !l l l re e ! ime har . re r i : l i c . .

Intcnnittcnt stlcam drainagesare a predomi

ni:urt tructurul lement f mountainousandscapes

in thc Pacitlc Northwest.Variation n fire severity at the scale of these small watershedsmaycontribute ignit icantlyo remnantrc cdcnsiti(]sand orerall habitatheterogeneity Ronme 1982.MorrisonandSwanson 990. urner t al. 199,1.

KushlaandRipple 1997, aylorandSkinner1998.Kccton 2000). Pattems of fire sevedt)' n thesesmallu'atersheds.owever. repoorlyunderstood.Th e central bjective f this studywas o quan-

tify fire sevedtypattems$,ithin the watershedsof internittent streamsn a recentlyburnedareain thc centralwestemCascades.

Documented re regimecharacteristicsbr thewatcrsheds l perennialsffeams uggest hat ireseverit)' s lower in riparianzones han in adja-

centuplands Campet al. 1997,WimberlyandSpies200l. Skinner2002).Riparian-associated

landtbrms ndvegetationonditions re hought1(r itigate fire severity Campet al. 1997,Impara1997,Kushlaan dRipplc 1997, aylorandSkin-ne r1998, eeton 000.Wimberly ndSpies 001.

Skinner2002, Lee and Smyth 2003).Higher hu-

midity, lower solarheating, he eft'ects fcold airdrainage. ydricsoils.abundant erbaceousnd

dce iJuouscge la l ion .ndh ighermoi \ tu re on-tent n both ivinganddeadwoody 'uelsmay allcontribute o apparently ower fire intensity and

severit),n these reasRomme1977.RommeaDdKni .eh t 981. gee t ;1 .2002 . Ber 'ausenter ' -mittcnt strcam channels n the study landscapearegenerally teeperandessoftenassociated,ith

humid riparian zonesand deciduous rees.ho\4-cvcr. wc predicted hat proximity to the steamchannel oesnot mitigate ire severity 'ithin hese

snall watelsheds.

StudyArea

We examincda portionol theWamerCreekFireon theWillametteNational Forest, 9 km eastof

Oakfidge n thc ccntralwesternCascade angeof Oregon. n this region, Iow summerraintall,castcrly winds. and lightning storms create a-vorablewildflre conditionsn latc summer nd

early fall. The Wamer Creek Fire was gnited b1'an arsonist n l0 October1991 ftera prolongcdperiodofhot, dry weatherand desiccatingwinds.

Dri\,enbl' a southwest 'ind. he ire raneastalong

the south aceofBunchgrassRidge.a north*estsouthcastrcnding idgc hat oughlybisccts hcfire arer.andnorth nto adjacent rainages. totalof 3,630 ha bumed befole rain showersslowedan dextinguishedhe ir eon 23 October. he irewas actively ought by the USDA ForestSerriceusing aerial etiLrdeurtropsand backlires USDA

Forest ervice 993). ecauseuppressionffbfts

were less ntensiveon the south side of Bulchgrass idgc, owcvcrwc think lrccffccls fsup-prcrs ion ct i r t i e . ' n i re .e rer i t r l l uern \n u fstudy areawere mininal.

The study area ncluded he watersheds f 33intermittentstreans nc;sed nto the steep. outh-southwcstaccof Bunchgrass idgc Fi-surc ).The averagewatershed ize s 16.2ha. andeler,a-tion ranges rom 800-1750m abovesea evel.Vegetationof the wcstcrn hemlock (fsir,qa

heten4 ryllu) zone s dominant n the study arca(Franklin ndDyrness 9lJll).Although vesternhemlockandwestem edcedarTlurjaplituttil are

common.shade-tolerantpecjesn this zone,Douglas-firmaintains ominanccn manystandsasa rcsultofits longevity elative o the requenc)offires thatcontinually esetsuccessionFianklin

an dHemstrom 91|]1).

Methods

Aerialphotographs erc used o quantifypattems

of fire severitywithin he ocalwatersheds.e-

causea fire of aparticular ntensity (e.g.,eoerg,vreleascdcrunitoffirc linc cngth)canhavcdiilcr-en teft-ectsn different lant peciesAgee1993).Wc quantified ire severity n tems of the eflectof the fire on Douglas fir, which is the dominant

canopyspeciesn the studyarea.Aerial photo-graphsof the Wamer Creek Fire area taker 1n1990. ne yearbefin the ire, nclicatcha t hewatersheds ad nearly complete orest co\,erbeforc Lhe um. Fire severiLywas herelbredelined

as he percentage f canopl' ffee cover hat sur-vived he ire.

Th e 33 sample trcams nd thcir watcrshcdboundarieswere drarvnon acetate hat overlaidI :12,000 oloracrialphotographsakcn n l99li.This photodate ndicates 'e sampled oth m-mediate reemo ality and nortalit.v of trees hat

occumed 7 yr atter he ire. Each watershedwasdividcd nto ourzones efined y andscapeo-

sition (sh'eamside r upland) and aspect south

eastor southwest-ti icing lope).The division

Fire Se\edty in lntenn ittent StreamDrainages 187

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i t ,U , !

E =

- ' '

:

zo(,IIJg.

o

l x x T , ' l l . t \ , ' n , \ \ rn .on . ndCi . .e l

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bet$een he streamside nd uplard zoneswa sdrawn halfway between he strcamchannelandthe dg clinc so that th e zoneswould be largeenough o visuallv estimate ive canopycovt:ronthe 1 12.000 erial hotographs.his esultednindividual zones overingslopcdistances f-50-100 m. Using a Stratexprismnirror stereoscopewith,lx binoculars, ercent ost-t ireiv e

canopycover in each of the four \\,atelshed ones wasvisuallyestimated ithin l0cqual intervals angingfrom 0-1007c e.g.,0-10%, I l-207o,etc.).Th enid-point of each ntervalwasused n statisticalanalysese.g.. - 07c= 5a/cl1 20c/c l5%. etc.).The direct and interactiveetTectsof landscapeposition streamside.upslope) ndaspcct south-

east . southwcst-tacinglope) n Iivec,ulopv o\er$,ere estedusing t\\"o way analysisof variancc(ANOVA) on thearcsine quarc-rootranstbrnreddata Za r 1999,SAS nstitute 995). he evelolsignil icance asselat P = 0.05.

To test he accuracyof the aerialphotograph

interpretation, ire severitydataobtained rom aerialphotographs crc conrpared ith lire severity ataobtained n the tleld. Six of the studywate$heds(totaling 10 3 ha. or 197c f thc arcasanpled)werc randomlyselectedbr ground-truthing.Percent ive canopycover was calculatcd n the ieldusinga MoosehomdensitometerGarrison19,191.Each watcrshcdwa s divided nt o a l0 x l0 m

grid, and a canopy reading was taken at everygrid nterscction. t eachpoint, he canopywa sopen f l ivc canopy il led less ha n half ol thesquares isible n the Moosehon grid,andclosedif live canopv illed half or more of the squares.Fielddrta werecollapsed nto the our watcrshedzonesused n thc acrialphotograph nalysis,and

thepercentagefclosedcanopy ointswithin eachzone wascalculated o obtain an estimaLc f live

canopy cover within eachzonc. Wc tested br acoraelation etween ivc canopycovercalculatedfrom tield data and ive canopy cover estimatedfrom aerialphotographsbr eiichwatershed oneusing Pearson roduct-moment orelation (Zar

1999,SAS Institute1995). hc levelof signif i-cancewa sse tat P = 0.05.

Results

Aerial photographdata revealedno significant

differencc n Jivecanopycover betweensffeam-

side and upland zoneson either the soulheast rsouthwest-facinglopcs f the sarnpled atersheds(Figure2). Wc observeda significantcorelationbctween ive canopycover calculated rom fielddataand ive canopycoverestimated rom acrialphotographsn eachof the tbur watershed ones(Pearson roductmoment corelation: r = 0.95-0 . 9 8 . N = 6 , P < 0 . 0 0 5 ) .

Figure 2. Niean ivc canopy colcr (+ I srandarderor) estinated fionl aerial fhorographs n strcamsidc nd

adjacentupland Toncson sourhcaslrnd soulhwesl acing slopesu ithin the $arersheds f 33 i.lcrmit

tent streams n the WarnerCreekFire studv arca.Jul! 2000.

tr sbeamside

I upslope

45

4 4 0(D ^-

+g t ob 2 5

3 z o

3 t sc

3 r oo

0

wesl-tacingslopes east-hcing lopes

Fire Severityn Intcmrittent treamDrainages 18 9

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Discuss ion

F-ire everitywlth n Watersheds

The watershedsncluded n this studyare ocatedin s teep. south-1acing. issected erain wherevegetationomposition nd environmentalon -ditions are similar along thc strcam and on the

rdjacent uplands. Solar radiation s high in thestud,varea and. by late sunmer, soil and fueJmoistureareextremely ow. The potential or ilr-termittent streamdrainages uchas hese o miti-gatc tirc scvcrity may be reducedby a lack ofnr i c roc i i t n r tend o l r r rn ro is lu rehr r i l c l (i \ l i (associated'ith riparianvegetation nd andfomscommonalongJarger,ower-gradienttreams.heextent o which fire severity s reducedalong streamdrainages n general. hcrcforc, mav dependonthe size of the streamand he degreeof differen-tiation betweendparian and upland fuel condi-tions. At the landscape cale.diflerences n fireseverityalong strcams f differentsizesare ikely

to nfluence he mosaicofpost fire vegetation ndcontribute o overallstructural iversity n for-estsof nountainous andscapes.

The conelation etweenlr e severity ataes -timated rom aerialphotographs nd ire severitydata obtained n the lield was signihcant, conllrming that acrial photographestimatesof livecanopy cover reflected actual conditions on theground.Although heremay have een orne e-la,ved o tality betweenhe ireyear 1991) ndtheycar hc acrialphotographs ere aken 1998),

u' eassumed osignitlcant hangen live canopycoverbctwccn1998and 2000.when ield sam-pling was conducted.

Potenta l\,4anagementmp cations

An alternative trategy1brmeeting he broadob-jectives f theNothwest ForcstPlan nvolves sing

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Fire Severity n IntermittentStreamDrainages l9l