Boreal forest resilience

Some initial thoughtsBNZ 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?

1900 1950 2000 2050 2100

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-20

24

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Year

Mar

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June

Mea

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CRU + GCM CompositeECHAM5HADCM3MIROC3.5GFDL2.1CGCM3.1

March-June Average Temperature (C°) Alaska: 1901-2099

Torre Jorgenson

Kenai bark beetle outbreak

Area burned in W. North America has doubled

in last 40 years

Rupp

We can expect more wildfire

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 coarse-

scale resilience?– e.g., shift to deciduous dominance maintains fire

as a critical forest process

Resilience & Ecosystem FeedbacksDominant species

RecruitmentInteractions

Competition, herbivory

Functional traits

Disturbance

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

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

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

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

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

Abrupt ecosystem shifts

From Tinner et al. 2008

Disturbance & climate interact to alter forest resilience

tundra black spruce deciduous

dynamic equilibrium

directional change

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

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