This document discusses a study that used a process-based vegetation model (LPJ-GUESS) to simulate the dynamics of forest composition on the Olympic Peninsula since the last glacial period (~15,000 years ago), and compare the simulations to paleoecological records. The study parameterized LPJ-GUESS for 9 tree species common to the region, considering each species' shade tolerance, temperature and moisture requirements. Simulation results showed good agreement with pollen-based reconstructions of forest changes over time for most sites and elevations. However, the model did not fully capture early Holocene dominance of Douglas-fir and alder at some mid-elevation sites. The study provides insights into how tree species life histories and climate

1. Postglacial
dynamics of
Olympic Peninsula
forests: comparing
simulations and
observations
Thanks to
Dan Gavin
Bart Bartlein
Jed Kaplan
A Master’s Thesis
presented to the
Department of Geography
University of Oregon
by
David Fisher

2. Olympic Mountains, WA

3. Research Questions
•
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?

4. Outline of this talk
• 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?

5. Paleoecological Records
Cold, Pollen Percentage Diagram
Yahoo Lake -Dry? Warm, Dry Cool, Wet
Figure by D. G. Gavin
(Gavin, D.G. 2013)

6. Limiting factors for tree growth:
On the west side: energy
On the east side: moisture
sretemoliK 08
04
02
0
¯
50km
PRISM
(Daly et al. 2008)
4
3
2
Potential
Natural
Forest Zones
¯
-4
0
-2
02
0
6 meters
04
PRISM
(Daly et al. 2008)
2 deg C
Mean Annual Precip
sretemoliK 08
Minimum Jan Temp
(Henderson et al. 2011)
Alpine
mountain hemlock
subalpine fir
Pacific silver fir
Douglas-fir
western hemlock
Sitka spruce

7. mountain hemlock
Tsuga mertensiana
western redcedar
Thuja plicata
subalpine fir
Abies lasciocarpa
western hemlock
Tsuga heterophylla
lodgepole pine
Pinus contorta
Sitka spruce
Picea sitchensis
Pacific silver fir
Abies amabilis
red alder
Alnus rubra
Douglas-fir
Pseudotsuga menziesii
grass

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

9. Methods: Considering the seedlings, how do we measure
energy?
Growing Degree Days
Average Daily
Temperature
(Deg C)
Post-Snow
Growing Degree Days
15
2000
Size of Snowpack
(Snow-Water equivalent)
(mm)
10
1000
5
-5
J F M A M J J A S O N D
0

10. Post-Snow GDD Measurements
Local Measurements of Post-Snow GDD
(two SNOTEL stations)
Year
2006
2007
2008
2009
2010
2011
2012
SW
487
373
650
NE
649
432
493
670
473
384
563
SW = Buckinghorse
NE = Waterhole
http://www.wcc.nrcs.usda.gov/snotel/SNOTEL-brochure.pdf

11. Post-Snow GDD Simulations
annual PS-GDD required
for each species to establish
# Post-Snow
GDDs
1600
1400
S. spruce
w. redcedar w. hemlock
r. alder
800
Doug-fir
300
m. hemlock l. pine
subalpine fir
Five Locations
Low - Wet
Mid - Wet
High - Wet
High - Dry
Low - Dry
−60
1890
−30
1920
0
1950
Year
30
1980
60
2010
P. silver fir

12. LPJ-GUESS: a process-based vegetation model
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.
http://www.nateko.lu.se/lpj-guess/education/html/guess.pdf

13. Process Parameters
title
nyear_spinup
vegmode
ifdailynpp
ifdailydecomp
ifbgestab
ifsme
ifstochmort
ifstochestab
estinterval
distinterval
iffire
ifdisturb
ifcalcsla
ifcdebt
npatch
patcharea
outputdirectory
ifsmoothgreffmort
ifdroughtlimitedestab
ifrainonwetdaysonly
ifspeciesspecificwateruptake
Shade Group Parameters (shadevintol, shadeintol, shadetol, shadevtol):
Title for run
Number of simulation years to spinup for
Vegetation mode ("INDIVIDUAL", "COHORT", "POPULATION")
Whether photosynthesis calculated daily (alt monthly)
Whether soil decomposition calculated daily (alt monthly)
Whether background establishment enabled (0,1)
Whether spatial mass effect enabled for establishment (0,1)
Whether mortality stochastic (0,1)
Whether establishment stochastic (0,1)
Interval for establishment of new cohorts (years)
Generic patch-destroying disturbance interval (years)
Whether fire enabled (0,1)
Whether generic patch-destroying disturbance enabled (0,1)
Whether SLA calculated from leaf longevity
Whether to allow C storage
Number of patches simulated
Patch area (m2)
Directory for the output files
Whether to vary mort_greff smoothly with growth efficiency (0,
Whether establishment drought limited (0,1)
Whether it rains on wet days only (1), or a little every day (0)
Whether or not there is species specific soil water uptake (0,1)
Global PFT Parameters:
lambda_max
emax
reprfrac
wscal_min
Non-water-stressed ratio of intercellular to ambient CO2 pp
Maximum evapotranspiration rate (mm/day)
Fraction of NPP allocated to reproduction
Water stress threshold for leaf abscission (raingreen PFTs)
Lifeform Parameters (Tree, Grass):
crownarea_max
ltor_max
k_allom2
k_allom3
k_rp
cton_leaf
cton_root
cton_sap
pathway
kest_repr
kest_bg
kest_pres
litterme
respcoeff
k_chilla
k_chillb
k_chillk
Maximum tree crown area (m2)
Non-water-stressed leaf:fine root mass ratio
Constant in allometry equations
Constant in allometry equations
Constant in allometry equations
Leaf C:N mass ratio
Fine root C:N mass ratio
Sapwood C:N mass ratio
Biochemical pathway ("C3" or "C4")
Constant in equation for tree estab rate
Constant in equation for tree estab rate
Constant in equation for tree estab rate
Litter moisture flammability threshold (fraction of AWC)
Respiration coefficient (0-1)
Constant in equation for budburst chilling time requirement
Coefficient in equation for budburst chilling time requirement
Exponent in equation for budburst chilling time requirement
turnover_sap
greff_min
est_max
alphar
parff_min
Sapwood turnover (fraction/year)
Threshold for growth suppression mortality (kgC/m2 leaf/yr)
Max sapling establishment rate (indiv/m2/year)
Shape parameter for recruitment-juv growth rate relationship
Min forest floor PAR for grass growth/tree estab (J/m2/day)
PFT (or species) specific parameters:
include
! Include PFT in analysis
phengdd5ramp
! GDD on 5 deg C base to attain full leaf cover
rootdist
! 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 equations
k_latosa
! Tree leaf to sapwood xs area ratio
sla
! 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 parameter
gdd5min_est
! Min GDD on 5 deg C base for establishment
longevity
! 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
! !
file_anpp
! !
file_lai
! !
file_cflux
! !
file_dens
! !
file_cpool
! !
file_runoff
! !
file_firert
! !
file_mnpp
! !
file_mlai
! !
file_mgpp
! !
file_mra
! !
file_maet
! !
file_mpet
! !
file_mevap
! !
file_mrunoff !
!
file_mintercep ! !
file_mrh
! !
file_mnee
! !
file_mwcont_upper
file_mwcont_lower
file_speciesheights
C biomass output file
Annual NPP output file
LAI output file
C fluxes output file
Tree density output file
Soil C output file
Runoff output file
Fire retrun time output file
Monthly NPP output file
Monthly LAI output file
Monthly GPP-LeafResp output file
Monthly autotrophic respiration output file
Monthly AET output file
Monthly PET output file
Monthly Evap output file
Monthly runoff output file
Monthly intercep output file
Monthly heterotrphic respiration output
Monthly NEE output file
Monthly wcont_upper output file
Monthly wcont_lower output file
Mean species heights in 2000
Climate Group Parameters (Boreal, Temperate):
pstemp_min
pstemp_low
pstemp_high
pstemp_max
Approximate low temp limit for photosynthesis (deg C)
Approx lower range of temp optimum for photosynthesis (deg C)
Approx higher range of temp optimum for photosynthesis (deg C)
Maximum temperature limit for photosynthesis (deg C)
Leaf Group Parameters (Broadleaf, Needleleaf):
gmin
phenology
turnover_root
intc
Canopy conductance not assoc with photosynthesis (mm/s)
Phenology ("EVERGREEN", "SUMMERGREEN", "RAINGREEN" or "ANY")
Fine root turnover (fraction/year)
Interception coefficient
Parameters of LPJ-GUESS
(Smith et al. 2001)

14. Parameterizing LPJ-GUESS, 9 different tree species
Shade&Tolerance
Min&Annual&Post4Snow&
GDD
%&available&
soil4water
Maximum&
Age
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
Intolerant
800
0.2
750
western'hemlock
Very&Tolerant
1400
0.6
400
western'redcedar
Tolerant
1400
0.5
1000
Very&Intolerant
1400
0.5
80
Tolerant
1600
0.7
500
lodgepole'pine
Douglas8fir
red'alder
Sitka'spruce

15. 14
12
10
JJA
8
6
4
SON
2
Temperature (C)
0
MAM
-2
-4
-6
-8
DJF
-10
-12
-14
-16
[decadal averages every 10 years]
-18
-20
2
Temperature (C)
0
Annual
-2
-4
-6
[-120.0, 46.389]
-8
-22
-20
-18
-16
-14
-12
-10
Age (-ka)
-8
-6
-4
-2
0
Figure by P.J. Bartlein

16. Results: present-day
Percent cover of tree species in
639 ecological plots in the
Olympic National Forest
(downloaded from Ecoshare.info)
East Side
West Side
1500
●
●
lodgepole pine
●
0
●
●
●
●
subalpine fir
●
●
●
●
●
mountain hemlock
●
elevation (meters)
Elevation (meters)
Simulated biomass of tree
species averaged over
the last 1000 years at each
site
●
●
●
●
Pacific silver fir
●
●
●
●
●
Douglas-fir
●
●
●
●
●
western hemlock
●
●
●
●
●
western redcedar
●
●
●
●
●
Sitka spruce
●
●
●
1500
●
●
red alder
●
0
●
●
0
25
50
75
0
25
50
% Cover in field plots (gray); Simulated biomass x 10 (black)
75

17. Percent of Total
< 0.5
0.5-2
2-10
10-50
Low Elevation, Wet Side
M = Model Results
D = Pollen Data
50-100
Low Elevation, Dry Side
M
D
grass
Grass
lodgepole pine
lodgepole pine
subalpine fir
subalpine fir
mountain hemlock
mountain hemlock
Pacific silver fir
Pacific silver fir
Douglas-fir
Douglas-fir
western hemlock
western hemlock
western redcedar
western redcedar
Sitka spruce
Sitka spruce
M
D
red alder
−15000
15,000
−10000
10,000
−5000
5000
0
0
red alder
−15000
15,000
Years before present
−10000
10,000
−5000
5000
0
0

18. Percent of Total
< 0.5
0.5-2
2-10
10-50
High Elevation, Wet Side
M = Model Results
D = Pollen Data
50-100
High Elevation, Dry Side
M
D
grass
grass
lodgepole pine
lodgepole pine
subalpine fir
subalpine fir
mountain hemlock
mountain hemlock
Pacific silver fir
Douglas-fir
Douglas-fir
western hemlock
western hemlock
western redcedar
M
D
Sitka spruce
−15000
15,000
−10000
10,000
−5000
5000
0
0
Sitka spruce
−15000
15,000
Years before present
−10000
10,000
−5000
5000
0
0

19. Mid Elevation, Wet Side
Late Glacial to late Holocene
transition is captured.....
M
D
grass
lodgepole pine
subalpine fir
mountain hemlock
But what about the abundant Douglas-fir and
alder pollen in the early Holocene
Pacific silver fir
Douglas-fir
western hemlock
western redcedar
M = Model Results
D = Pollen Data
Sitka spruce
M
D
red alder
−15000
−10000
15,000
10,000
−5000
0
5000
0
Years before present

20. At the Mid elevation, Wet Side site
Jan & July Temperature
Deg C
Jan & July Precipitation
22
20
18
16
14
12
10
8
6
4
2
0
−2
−4
−6
−8
−10
−15000
600
mm
400
200
0
−10000
−5000
Years before present
0
−15000
−10000
−5000
Years before present
0

21. Fraction
available
soil-water
Post-snow
GDD
1600
S. spruce
w. redcedar r. alder
1400 w. hemlock
S. spruce P. silver fir m. hemlock
0.7
w. hemlock
800
Doug-fir
P. silver fir
300 m. hemlock
l. pine
subalpine fir
subalpine fir
Simulated
Biomass
Kg C per
square
meter
−15000
−10000
w. redcedar
r. alder
0.5
Low - Wet
Mid - Wet
−20000
0.6
−5000
0
20
High - Wet
Doug-fir
−20000
0.2
0.15
l. pine
−15000
−10000
−5000
0
Fire Return
Time (years)
High - Dry
Low - Dry
15
900
10
600
5
300
0
−20000
−15000
20,000
15,000
−10000
10,000
−5000
5000
0
0
−20000
20,000
−15000
15,000
−10000
10,000
−5000
5000
0
0

22. The influence of snow
• The two climate variables that are controlling species composition
across the Peninsula are both influenced by snowpack
Rain-Snow Temp
More Snow
+2
+1
0
-1
Less Snow
-2

23. Fraction
available
soil-water
1600
Post-snow
GDD
1400
0.7
800
0.6
0.5
300
0.2
0.15
−20000
20,000
−15000
−10000
15,000
−5000
10,000
5000
0
−20000
−15000
−10000
−5000
0
0
Fire Return
Time (years)
Scenarios with varying Rain-Snow temp
threshold at the high elevation wet site
More Snow
900
+2
600
+1
0 °C
300
-1
Less Snow
-2
−20000
−15000
−10000
20,000
15,000
10,000
−5000
5000
0
0

24. Scenarios with varying Rain-Snow temp
threshold at the high elevation wet site
Thresholds crossed
0°C to 1°C
enough snow to favor mountain
hemlock (by limiting others)
10.0
7.5
variable
Simulated
Biomass
Pacific silver fir
subalpine fir
lodgepole pine
Douglas-fir
mountain hemlock
grass
5.0
Kg C per
square
meter
2.5
0.0
−2
Less Snow
−1
0
1
Rain-Snow Temp
°C
2
More Snow
1°C to 2°C
too much snow for consistent forest
cover, open canopy plants thrive (grass
and pine)

25. What did we learn?
•
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

26. 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.