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Boreal forest resilience
Some initial thoughtsBNZ LTER meeting, March 2009
Terry Chapin & Jill Johnstone
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Is the boreal forest vulnerable to climate change?
• Is the degree of exposure high? Yes• Is it sensitive to changing climate? Yes• Does it have the diversity to adapt to change?
– Species diversity?– Functional diversity?– Landscape diversity?
• Roles of local adjustment, migration, and invasion?
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1900 1950 2000 2050 2100
-6-4
-20
24
68
Year
Mar
ch t
hru
June
Mea
n Te
mpe
ratu
re (
C)
CRU + GCM CompositeECHAM5HADCM3MIROC3.5GFDL2.1CGCM3.1
March-June Average Temperature (C°) Alaska: 1901-2099
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Torre Jorgenson
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Kenai bark beetle outbreak
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Area burned in W. North America has doubled
in last 40 years
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Rupp
We can expect more wildfire
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Rural communities have locations fixed by infrastructure
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People’s fine-scale relationship with fire has changed over time
• Pre-contact: Mobile family groups– People adjust to fire regime
• 1950s: Consolidation in permanent settlements– Fire affects communities
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Wildfire options in 20-50 years?
• Maintain same fire regime as today?– ~20-fold increase in cost
• Maintain current budget for suppression?– Reduce area protected despite rising population
• Change landscape pattern of fire?– Increase landscape heterogeneity: reduce risk of huge fires– Requires community engagement in fire planning
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How resilient is the boreal forest to climate change?
• Does it have the adaptive capacity to adjust?• What components will be resilient and what
will transform?• Can fine-scale change contribute to coarse-
scale resilience?– e.g., shift to deciduous dominance maintains fire
as a critical forest process
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Resilience & Ecosystem FeedbacksDominant species
RecruitmentInteractions
Competition, herbivory
Functional traits
Disturbance
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Black spruce dominant
Local seed rain
Growth & survival
FIRE
Poor quality seedbeds (organic soil)
Slow growthLow competition
High moistureHigh mossCool soils
Resilience cycles in black spruce
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Black spruce dominant
Local seed rain
Growth & survival
FIRE
Poor quality seedbeds
(organic soil)
Slow growthLow competition
High moistureHigh mossCool soils
Black spruce forests
Deciduous dominant
Resprouting & seed dispersal
Growth & survival
High quality seedbeds (mineral soil)
Rapid growthHigh competition
Low moistureRapid cyclingWarm soils FIRE
Deciduous forests
Contrasting plant resilience cycles
severe fire
long fire interval
short fire interval
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Thick organic layer
Cool, moist soils
Slow decomposition
Slow nutrient turnover
High moss NPP
Low severity fire
High severity fire
Long fire-free interval
Thick organic layer
Shallow organic layer
Warm, well-drained soils
Rapid decomposition
High nutrient turnover
High vascular plant NPP
High litter production
Low moss NPP
Shallow organic layer
Resilience cycles mediated by soil
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Time
disturbance
Hidden changes in resilience yield ecological surprises
Rel
ativ
e sp
ecie
s do
min
ance
Undisturbed trajectory
Disturbed trajectory
Directional change in recruitment potential
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Detailed paleo-records are often consistent with resilience thresholds
Species abundance 1
Spe
cies
abu
ndan
ce
2
Species abundance 1S
peci
es a
bund
ance
21K
5K
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Abrupt ecosystem shifts
From Tinner et al. 2008
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Disturbance & climate interact to alter forest resilience
tundra black spruce deciduous
dynamic equilibrium
directional change
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Landscapes will have variable resilience
well drained
moderately drained
poorly drained
b. Pre-fire organic layer depth
c. Propagation potential of smouldering combustion
d. Magnitude of severity effects
a. Landscape moisture gradient
(-)
(+)
Example: Ecosystem sensitivity to surface fuel consumption
high resilience
high resilience
low resilience
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Summary of Points
• Biotic and abiotic elements interact to determine resilience– What interactions are most critical?– Do we know enough to predict these?– Can we test our predictions?
• Strong interactions may maintain non-equilibrium ecosystems– “Hidden” changes in resilience– Sudden responses – Possibly (often?) catalyzed by disturbance