Postglacial dynamics of

Olympic Peninsula forests: comparing

simulations and observations

A Master’s Thesis presented to the

Department of Geography University of Oregon

byDavid Fisher

Thanks toDan Gavin

Bart BartleinJed Kaplan

Olympic Mountains, WA

• How does knowledge of the life history of tree species -- regeneration, growth, competition, mortality -- as well as the relationship between species and climate at important life stages, improve our explanation of the dynamic changes in forest composition since the Late Glacial period, 15,000 years ago?

Research Questions

• Paleoecology & Biogeography of Olympic Peninsula forests

• Methods -- quantifying important bioclimatic variables and simulating paleoecological records with a process-based vegetation model

• Results -- Simulations compared to present and paleo records

• What did we learn?

Outline of this talk

Paleoecological Records

Yahoo Lake - Pollen Percentage Diagram

Figure by D. G. Gavin

Cold, Dry? Warm, Dry Cool, Wet

(Gavin, D.G. 2013)

Limiting factors for tree growth: On the west side: energy On the east side: moisture

¯0 40 8020 Kilometers

¯0 40 8020 Kilometers

¯0 40 8020 Kilometers

0

2 deg C

-4

-2

4

6 meters

2

3

Alpinemountain hemlocksubalpine fir

Pacific silver fir

Douglas-firwestern hemlockSitka spruce

Minimum Jan Temp Mean Annual Precip Potential Natural Forest Zones

50km

(Henderson et al. 2011)

PRISM (Daly et al. 2008)

PRISM (Daly et al. 2008)

lodgepole pinePinus contorta

subalpine firAbies lasciocarpa

mountain hemlockTsuga mertensiana

Pacific silver firAbies amabilis

Douglas-firPseudotsuga menziesii

western redcedarThuja plicata

western hemlockTsuga heterophylla

Sitka sprucePicea sitchensis

red alderAlnus rubra

grass

Methods: Considering the seedling, how should we measure energy and moisture requirements?

Growing Degree Days

FJ M A M J J A S O N D

5

-5

10

15Average Daily Temperature

(Deg C)

Post-Snow Growing Degree Days

0

1000

2000Size of Snowpack

(Snow-Water equivalent)

Methods: Considering the seedlings, how do we measure energy?

(mm)

Local Measurements of Post-Snow GDD

(two SNOTEL stations)

Year SW NE2006 6492007 4322008 4932009 6702010 487 4732011 373 3842012 650 563

Post-Snow GDD Measurements

SW = BuckinghorseNE = Waterhole http://www.wcc.nrcs.usda.gov/snotel/SNOTEL-brochure.pdf

−60 −30 0 30 60

w. hemlockS. sprucew. redcedarr. alder

P. silver firDoug-fir

m. hemlock l. pinesubalpine fir

1600

1400

800

300

1890 1920 1950 1980 2010

Post-Snow GDD Simulations

Low - Dry

High - Dry

High - Wet

Mid - Wet

Low - Wet

Five Locations

Year

# Post-Snow GDDs

annual PS-GDD required for each species to establish

Cohorts of trees grow on patches of land (15m x 15m).

Each species is unique in its ability to establish, grow, and die.

Continuous Climate (temperature, precipitation, cloudiness) is the main driver.

LPJ-GUESS: a process-based vegetation model

http://www.nateko.lu.se/lpj-guess/education/html/guess.pdf

Process Parameters

title Title for runnyear_spinup Number of simulation years to spinup forvegmode Vegetation mode ("INDIVIDUAL", "COHORT", "POPULATION")ifdailynpp Whether photosynthesis calculated daily (alt monthly)ifdailydecomp Whether soil decomposition calculated daily (alt monthly)ifbgestab Whether background establishment enabled (0,1)ifsme Whether spatial mass effect enabled for establishment (0,1)ifstochmort Whether mortality stochastic (0,1)ifstochestab Whether establishment stochastic (0,1)estinterval Interval for establishment of new cohorts (years)distinterval Generic patch-destroying disturbance interval (years)iffire Whether fire enabled (0,1)ifdisturb Whether generic patch-destroying disturbance enabled (0,1)ifcalcsla Whether SLA calculated from leaf longevityifcdebt Whether to allow C storagenpatch Number of patches simulatedpatcharea Patch area (m2)outputdirectory Directory for the output filesifsmoothgreffmort Whether to vary mort_greff smoothly with growth efficiency (0,ifdroughtlimitedestab Whether establishment drought limited (0,1)ifrainonwetdaysonly Whether it rains on wet days only (1), or a little every day (0)ifspeciesspecificwateruptake Whether or not there is species specific soil water uptake (0,1)

Global PFT Parameters:

lambda_max Non-water-stressed ratio of intercellular to ambient CO2 ppemax Maximum evapotranspiration rate (mm/day)reprfrac Fraction of NPP allocated to reproductionwscal_min Water stress threshold for leaf abscission (raingreen PFTs)

Lifeform Parameters (Tree, Grass):

crownarea_max Maximum tree crown area (m2)ltor_max Non-water-stressed leaf:fine root mass ratiok_allom2 Constant in allometry equationsk_allom3 Constant in allometry equationsk_rp Constant in allometry equationscton_leaf Leaf C:N mass ratiocton_root Fine root C:N mass ratiocton_sap Sapwood C:N mass ratiopathway Biochemical pathway ("C3" or "C4")kest_repr Constant in equation for tree estab ratekest_bg Constant in equation for tree estab ratekest_pres Constant in equation for tree estab ratelitterme Litter moisture flammability threshold (fraction of AWC)respcoeff Respiration coefficient (0-1)k_chilla Constant in equation for budburst chilling time requirementk_chillb Coefficient in equation for budburst chilling time requirementk_chillk Exponent in equation for budburst chilling time requirement

Climate Group Parameters (Boreal, Temperate):

pstemp_min Approximate low temp limit for photosynthesis (deg C)pstemp_low Approx lower range of temp optimum for photosynthesis (deg C)pstemp_high Approx higher range of temp optimum for photosynthesis (deg C)pstemp_max Maximum temperature limit for photosynthesis (deg C)

Leaf Group Parameters (Broadleaf, Needleleaf):

gmin Canopy conductance not assoc with photosynthesis (mm/s)phenology Phenology ("EVERGREEN", "SUMMERGREEN", "RAINGREEN" or "ANY")turnover_root Fine root turnover (fraction/year)intc Interception coefficient

Shade Group Parameters (shadevintol, shadeintol, shadetol, shadevtol):

turnover_sap Sapwood turnover (fraction/year)greff_min Threshold for growth suppression mortality (kgC/m2 leaf/yr)est_max Max sapling establishment rate (indiv/m2/year)alphar Shape parameter for recruitment-juv growth rate relationshipparff_min Min forest floor PAR for grass growth/tree estab (J/m2/day)

PFT (or species) specific parameters:

include ! Include PFT in analysisphengdd5ramp ! GDD on 5 deg C base to attain full leaf coverrootdist ! Fraction of roots in each soil layer (first value=upper layer)turnover_leaf ! Leaf turnover (fraction/year)wooddens ! Sapwood and heartwood density (kgC/m3)k_allom1 ! Constant in allometry equationsk_latosa ! Tree leaf to sapwood xs area ratiosla ! Specific leaf area (m2/kgC)fireresist ! Fire resistance (0-1)tcmin_surv ! Min 20-year coldest month mean temp for survival (deg C)tcmin_est ! Min 20-year coldest month mean temp for establishment (deg C)tcmax_est ! Max 20-year coldest month mean temp for establishment (deg C)twmin_est ! Min warmest month mean temp for establishment (deg C)twminusc ! Stupid larch parametergdd5min_est ! Min GDD on 5 deg C base for establishmentlongevity ! Expected longevity under lifetime non-stressed conditions (yr)leaflong ! Leaf longevity (years)drought_tolerance!Drought tolerance level (0 = very -> 1 = not at all) (unitless)

Output Files:

file_cmass ! ! C biomass output filefile_anpp ! ! Annual NPP output filefile_lai ! ! LAI output filefile_cflux ! ! C fluxes output filefile_dens ! ! Tree density output filefile_cpool ! ! Soil C output filefile_runoff ! ! Runoff output filefile_firert ! ! Fire retrun time output filefile_mnpp ! ! Monthly NPP output filefile_mlai ! ! Monthly LAI output filefile_mgpp ! ! Monthly GPP-LeafResp output filefile_mra ! ! Monthly autotrophic respiration output filefile_maet ! ! Monthly AET output filefile_mpet ! ! Monthly PET output filefile_mevap ! ! Monthly Evap output filefile_mrunoff ! ! Monthly runoff output filefile_mintercep ! ! Monthly intercep output filefile_mrh ! ! Monthly heterotrphic respiration outputfile_mnee ! ! Monthly NEE output filefile_mwcont_upper Monthly wcont_upper output filefile_mwcont_lower Monthly wcont_lower output filefile_speciesheights Mean species heights in 2000

Parameters of LPJ-GUESS(Smith et al. 2001)

Parameterizing LPJ-GUESS, 9 different tree species

Shade&ToleranceMin&Annual&Post4Snow&

GDD%&available&soil4water

Maximum&Age

lodgepole'pine Very&Intolerant 300 0.15 250

subalpine'fir Very&Tolerant 300 0.5 250

mountain'hemlock Very&Tolerant 300 0.68 400

Pacific'silver'fir Very&Tolerant 800 0.7 400

Douglas8fir Intolerant 800 0.2 750

western'hemlock Very&Tolerant 1400 0.6 400

western'redcedar Tolerant 1400 0.5 1000

red'alder Very&Intolerant 1400 0.5 80

Sitka'spruce Tolerant 1600 0.7 500

-22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0Age (-ka)

-8

-6

-4

-2

0

2

Temperature(C)

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Temperature(C)

Annual

DJF

JJA

SON

MAM

[-120.0, 46.389]

[decadal averages every 10 years]

Figure by P.J. Bartlein

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0 25 50 75 0 25 50 75% Cover in field plots (gray); Simulated biomass x 10 (black)

elev

atio

n (m

eter

s)

lodgepole pine

subalpine fir

mountain hemlock

Pacific silver fir

Douglas-fir

western hemlock

western redcedar

Sitka spruce

red alder

West Side East SidePercent cover of tree species in 639 ecological plots in the Olympic National Forest (downloaded from Ecoshare.info)

Simulated biomass of tree species averaged overthe last 1000 years at each site

0

1500

0

1500

Elev

atio

n (m

eter

s)

Results: present-day

< 0.5 50-10010-502-100.5-2

−15000 −10000 −5000 0−15000 −10000 −5000 0

Grass

lodgepole pine

subalpine fir

mountain hemlock

Pacific silver fir

Douglas-fir

western hemlock

western redcedar

Sitka spruce

red alder

grass

lodgepole pine

subalpine fir

mountain hemlock

Pacific silver fir

Douglas-fir

western hemlock

western redcedar

Sitka spruce

red alder

Low Elevation, Wet Side Low Elevation, Dry Side

Percent of Total

15,000 10,000 5000 0 15,000 10,000 5000 0

Years before present

MD

MD

M = Model ResultsD = Pollen Data

−15000 −10000 −5000 0−15000 −10000 −5000 0

grass

lodgepole pine

subalpine fir

mountain hemlock

Douglas-fir

western hemlock

western redcedar

Sitka spruce

grass

lodgepole pine

subalpine fir

mountain hemlock

Pacific silver fir

Douglas-fir

western hemlock

Sitka spruce

High Elevation, Wet Side High Elevation, Dry Side

15,000 10,000 5000 0 15,000 10,000 5000 0

< 0.5 50-10010-502-100.5-2

Percent of Total

Years before present

MD

MD

M = Model ResultsD = Pollen Data

−15000 −10000 −5000 0

grass

lodgepole pine

subalpine fir

mountain hemlock

Pacific silver fir

Douglas-fir

western hemlock

western redcedar

Sitka spruce

red alder

Mid Elevation, Wet Side

Late Glacial to late Holocenetransition is captured.....

But what about the abundant Douglas-fir and alder pollen in the early Holocene

15,000 10,000 5000 0

Years before present

MD

MD

M = Model ResultsD = Pollen Data

0

200

400

600

−15000 −10000 −5000 0

−10−8−6−4−20246810121416182022

−15000 −10000 −5000 0

Deg C mm

Jan & July Temperature Jan & July Precipitation

Years before present Years before present

At the Mid elevation, Wet Side site

−20000 −15000 −10000 −5000 0−20000 −15000 −10000 −5000 0

−20000 −15000 −10000 −5000 0−20000 −15000 −10000 −5000 0

S. spruce

w. hemlockw. redcedar r. alder

P. silver firDoug-fir

m. hemlockl. pine

subalpine fir

S. spruce

w. hemlock

m. hemlockP. silver fir

subalpine fir w. redcedar r. alder

Doug-firl. pine

1600

1400

800

300

0.7

0.6

0.5

0.20.15

900

600

300

Low - Dry

High - Dry

High - Wet

Mid - Wet

Low - Wet

15

10

5

0

20

Post-snow GDD

Simulated Biomass

Kg C per square meter

Fraction available

soil-water

Fire Return Time (years)

15,000 10,000 5000 020,000 15,000 10,000 5000 020,000

+2

-2

-1

0

+1More Snow

Less Snow

Rain-Snow Temp

• The two climate variables that are controlling species composition across the Peninsula are both influenced by snowpack

The influence of snow

−20000 −15000 −10000 −5000 0

−20000 −15000 −10000 −5000 0−20000 −15000 −10000 −5000 0

15,000 10,000 5000 020,000

900

600

300

Fire Return Time (years)

0.7

0.6

0.5

0.20.15

Fraction available

soil-water

1600

1400

800

300

Post-snow GDD

15,000 10,000 5000 020,000

+2

-2

-1

0

+1More Snow

Less Snow

Scenarios with varying Rain-Snow temp threshold at the high elevation wet site

°C

0.0

2.5

5.0

7.5

10.0

−2 −1 0 1 2

variable

Pacific silver firsubalpine firlodgepole pineDouglas-firmountain hemlockgrass

Simulated Biomass

Kg C per square meter

Rain-Snow Temp°C

More SnowLess Snow

Thresholds crossed

0°C to 1°Cenough snow to favor mountain hemlock (by limiting others)

1°C to 2°Ctoo much snow for consistent forest cover, open canopy plants thrive (grass and pine)

Scenarios with varying Rain-Snow temp threshold at the high elevation wet site

• Supported the theory that energy requirements control species composition on the west side, and moisture controls composition on the east side

• Quantified the climatic tolerance of seedlings in terms of one specific energy-related climate variable (Post-snow GDD) and one moisture-related variable (fraction available soil-water)

• Provided the first species-level test against the paleoecological record of the influence of these climate variables

What did we learn?

Thank You!References

Daly, C., M. Halbleib, J. I. Smith, W. P. Gibson, M. K. Doggett, G. H. Taylor, J. Curtis, and P. P. Pasteris. 2008. “Physiographically Sensitive Mapping of Climatological Temperature and Precipitation Across the Conterminous United States.” International Journal of Climatology 28 (15) (December): 2031–2064. doi:10.1002/joc.1688.

Gavin, D. G., L. B. Brubaker, and D. N. Greenwald. 2013. “Postglacial Climate and Fire- Mediated Vegetation Change on the Western Olympic Peninsula, Washington.” Ecological Monographs (April 18). doi:10.1890/12-1742.1.

Henderson, J.A., R.D. Lesher, D.H. Peter, and C.D. Ringo. 2011. “A Landscape Model for Predicting Potential Natural Vegetation of the Olympic Peninsula USA Using Boundary Equations and Newly Developed Environmental Variables”. USDA General Technical Report: PNW-GTR-941. USDA Forest Service.

Liu, Z., B. L. Otto-Bliesner, F. He, E. C. Brady, R. Tomas, P. U. Clark, A. E. Carlson, et al. 2009. “Transient Simulation of Last Deglaciation with a New Mechanism for Bolling-Allerod Warming.” Science 325 (5938) (July 16): 310–314. doi:10.1126/science.1171041.

Smith, B., Prentice, I.C. & Sykes, M.T. 2001. Representation of vegetation dynamics in modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space. Global Ecology and Biogeography 10: 621-637.