Transcript Slide 1

Boreal forest resilience
Some initial thoughts
BNZ LTER meeting, March 2009
Terry Chapin & Jill Johnstone
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?
8
March-June Average Temperature (C°) Alaska:
1901-2099
-6
-4
-2
0
2
4
6
CRU + GCM Composite
ECHAM5
HADCM3
MIROC3.5
GFDL2.1
CGCM3.1
1900
1950
2000
Year
2050
2100
Torre Jorgenson
Kenai bark beetle outbreak
Area burned in W. North
America has doubled
in last 40 years
We can expect more wildfire
Rupp
Rural communities have locations fixed by infrastructure
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
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
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 coarsescale resilience?
– e.g., shift to deciduous dominance maintains fire
as a critical forest process
Resilience & Ecosystem Feedbacks
Dominant
species
Disturbance
Functional
traits
Interactions
Competition, herbivory
Recruitment
Resilience cycles in black spruce
Black spruce
dominant
FIRE
High moisture
High moss
Cool soils
Poor quality seedbeds
(organic soil)
Growth &
survival
Slow growth
Low competition
Local seed
rain
Contrasting plant resilience cycles
Black spruce forests
long fire interval Deciduous forests
Black spruce
dominant
High moisture
High moss
Cool soils
short fire
interval
FIRE
Low moisture
Rapid cycling
Warm soils
Deciduous
dominant
Local seed
rain
Growth &
survival
Slow growth
Low competition
FIRE
Resprouting &
seed dispersal
Growth &
survival
Poor quality
seedbeds
(organic soil)
Rapid growth
High competition
severe fire
High quality
seedbeds
(mineral soil)
Resilience cycles mediated by soil
Thick organic layer
Shallow organic layer
Long firefree interval
High moss
NPP
Low moss
NPP
High litter
production
Low severity
fire
Slow nutrient
turnover
Thick
organic layer
High severity
fire
Slow
decomposition
Cool, moist
soils
High vascular
plant NPP
Shallow
organic layer
Warm, welldrained soils
High nutrient
turnover
Rapid
decomposition
Relative species dominance
Hidden changes in resilience yield
ecological surprises
Undisturbed trajectory
Disturbed trajectory
Directional change in
recruitment potential
disturbance
Time
5K
1K
Species abundance 1
Species abundance 2
Species abundance 2
Detailed paleo-records are often
consistent with resilience thresholds
Species abundance 1
Abrupt ecosystem shifts
From Tinner et al. 2008
Disturbance & climate interact
to alter forest resilience
dynamic
equilibrium
directional
change
tundra
black spruce
deciduous
Landscapes will have variable
resilience
a. Landscape moisture gradient
w ell drained
moderately
drained
poorly drained
b. Pre-fire organic layer depth
high
resilience
c. Propagation potential of smouldering combustion
high
resilience
low resilience
d. Magnitude of severity eff ects
(+)
(-)
Example: Ecosystem sensitivity to surface fuel consumption
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