Recruitment of subalpine tree populations
sensitive to warming within and above current
altitudinal range
Help!
Is this lovely?
Lara M. Kueppers
Cristina Castanha, Erin Conlisk, Andrew Moyes, Matt Germino, Margaret Torn, John Harte, Jeffry Mitton UC Merced, LBNL, USGS, UC Berkeley, Univ of Colorado Photo: J. Mitton
Forest upslope migration
Temperature effect on advance
Mean growing season soil T (°C)
upslope with warming?
Absolute tree limit:
Growing season
soil T ~ 6.5 °C
Cold
Warm
Photo: A. Moyes
(Korner et al., 2004; Harsch et al. 2009)
Hypotheses re: role of seedlings
1.  Seedling dynamics are ephemeral and do not
affect treeline change
2.  Seedlings are ubiquitous and recruitment is
stochastic; climate effects minimally important
3.  Episodic good years are sufficient to grow or
maintain populations of long-lived trees
4.  Climatic constraint at treeline predominantly
temperature
1. Seedling dynamics are ephemeral and do
not affect treeline change Alternative hypothesis
Seedling recruitment
important to population
sizes Meta-population model with field data
Alpine
Treeline
Forest
50 ha
Initially no individuals, relies on
dispersal from treeline site
Initially few adult trees,
mostly large saplings
Initially many adult
trees
Differences in recruitment affect population sizes
50 ha
Generous assumptions
for dispersal to alpine
Abundance of trees ≥4 cm dbh in 50 ha
120,000
Alpine
80,000
40,000
0
150,000
0
100
200
300
400
500
Treeline
100,000
50,000
0
20,000
0
100
200
300
400
500
Forest
15,000
10,000
5,000
0
0
100
200
300
Time (years)
400
500
2. Seedlings ubiquitous, recruitment
stochastic, climate unimportant
Alternative hypothesis
Seedling success is
highly sensitive to
microclimate factors
Common garden-climate experiment 3 m 2 m Alpine, 3540 m IR Heater Soil moist. and temp. Treeline, 3430 m Control Heated Watered (2.5 mm/wk) Heated-­‐Watered First seeds sown in Fall 2009. Forest, 3060 m Figure: Andrew Moyes, Erin Conlisk
Suboptimal microclimate reduces limber pine
carbon uptake
Treeline
Freezing 2%
Low or high temperature
14%
Low moisture
21%
(Moyes et al. in revision)
Heat reduced first-year limber pine survival
0.2 Alpine
0.1 0 0.3 Treeline
0.2 0.1 0 0.2 Forest
Germination and First-Year Survival
Roughly 16,000 seeds were sown from 2009-2013
0.1 9 weeks
1 cm
0 Photo: Cristina Castanha
Control Water
Heat
Heatwater Heat, water alter first-year Engelmann spruce survival
0.05 Alpine
0.025 0 0.05 Treeline
0.025 0 0.05 Forest
Photo: Glenn F. Cowan
Germination and First-Year Survival
Roughly 29,000 seeds were sown from 2009-2013
0.025 9 weeks
0 1 cm
Photo: Cristina Castanha
Control Water
Heat
Heatwater
3. Episodic good years sufficient to grow or
maintain tree populations
Alternative hypothesis
Many good years in a
row required; Climate
change “loading the
dice”
Lodgepole pine expansion into meadows
c
100
80
Observed
Modeled
Best statistical model of 20th c.
population growth includes 9
years of favorable climate
40
60
Observed
Modeled
20
# of Recruits
c
0
000
combined
(seed and establishment)
1920
1940
1960
1980
2000
Year
(Lubetkin et al. in prep)
Interannual variation in survival and multi-year
effects of climate treatments#
Heating effect transient; watering effect emerges over time
0.3 1.0 Control Watered Heated HeatWater Limber pine
Cumula=ve Survival Survival Year 0-1 (+/-SE)
Alpine
0.2 0.1 0 2010 Seed sown
2011 2012 2013 4. Temperature predominant limiting factor at
treeline
Alternative hypothesis
Temperature interacts with other factors – soil
moisture under-appreciated
Treatments alter spruce population
sizes
(Conlisk et al. in prep)
Abundance of trees ≥4 cm dbh in 50 ha
50 ha
Control Heated Watered (2.5 mm/wk) Heated-­‐Watered 80,000
Alpine
40,000
0
150,000
100,000
50,000
0
80,000
60,000
Treeline
Forest
40,000
20,000
0
0
100 200 300 400 500
Years
Understanding climate effects on
seedling dynamics is important to
predicting treeline change.
(Smith et al. 2009; Harsch & Bader 2011)
Thank you!
DOE Office of Science, Terrestrial Ecosystem Science
Univ of Colo, Mountain Research Station and Niwot Ridge LTER
Scott Ferrenberg, Ethan Brown, Andrea Campanella, B. Kimball
(USDA), D. S. Christianson (UCB), J. Norris (UCM), M. McLaughlin
(USFS CDA Nursery), A. Schoettle (USFS), and many fantastic field
technicians
https://alpine.ucmerced.edu/pub/htdocs/index.html