Population dynamics across tree elevational ranges:
implications for climate change responses
Steve J. Kroiss, Leander DL Anderegg, Ian Breckheimer, Posy Busby,
Cynthia Chang, Kevin Ford, Evan Fricke, Melanie Harsch, Elli Theobald,
Janneke Hille Ris Lambers
University of Washington - Seattle
MtnClim – September 2014
Projecting climate induced range shifts
• Ranges shifting
poleward & upward
• But shifts not universal
Parmesan et al. 1999; Thomas et al. 2003; Moritz et al. 2008
How rapidly can populations respond?
Climate ‘niche’
Climate change
Population growth
Population decline
Hotter
Temperature
Colder
Range position
growth
decline
Range position
Fecundity
Survival
Population
Growth
growth
Need: an explicitly demographic approach
Range position
Understanding tree responses
to climate change
• Why trees/forests?
• What we know:
– Growth decreases with
elevation
– Mortality rates
increasing rapidly in
western US
Ford et al. 2014; van Mantgem 2009
No population dynamic studies across
tree ranges
• What we don’t know:
– Importance of different life
history stages
– Effect of pop. composition
(stage distributions)
fecundity
Trailing range edge
survival
growth
– All vital rates
– Integration into population
growth rates (λ)
Range position
λ
Range position
?
Range position
Leading range edge
Range position
Objectives
1. Assess variation in vital rates and population
growth rates across range position
2. Assess the sensitivity of population growth
rates to individual vital rates
3. Assess importance of population composition
(stage distributions) at range edges for
influencing population projections
Methods: Demography across altitudinal range limits
Pacific silver fir (Abies amabilis)
Methods: Demography across altitudinal range limits
Sapling growth &
mortality
Tree growth / mortality
35 years
Seed production &
seedling dynamics
5 years
Assessing population dynamics with
integral projection models
Hierarchical Bayesian modeling
approach
• Vital rates size specific
• Non-linear complex datasets
• Accounting for measurement error
Objectives
1. Assess variation in vital rates and population
growth rates across range position
2. Assess the sensitivity of population growth
rates to individual vital rates
3. Assess importance of stage distributions at
range edges for influencing population
projections
Adult survival
peaks at the leading range edge
Adult growth was highest in the range
center
Fecundity does not vary significantly
across range position
Population growth rate (λ)
Population growth rate
peaks at leading range edge
Recent
warming?
What are population growth rates
most sensitive to?
Population composition (unstable stage distributions)
work against range shifts
Adults only
(expected at
trailing edge)
Stable stage
distribution
Seedlings only
(expected at
leading edge)
Projections for tree range dynamics
• Low mortality implies extremely slow shifts at trailing
range edges
• Population growth rates peak at leading range edge
(climate change?)
• Sensitivity to young & understudied stages (seedlings &
saplings)
• Unstable stage distributions will work against range
shifts
Thanks to…
• Past and present members of the Hille Ris
Lambers lab
• Pacific Northwest Forest Permanent Sample
Plot Network