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How do forest ecosystems respond to environmental change?. Resilience & Ecosystem Feedbacks. Dominant species. Disturbance. Functional traits. Recruitment. Interactions. Competition. Aerial seed bank. Low nutrient cycling. Cold soils. Recruitment on organic soils. Conservative growth.

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resilience ecosystem feedbacks
Resilience & Ecosystem Feedbacks

Dominant species

Disturbance

Functional traits

Recruitment

Interactions

Competition

resilience feedbacks

Aerial seed bank

Low nutrient cycling

Cold soils

Recruitment on organic soils

Conservative growth

Mosses accumulate

Resilience Feedbacks

Black spruce

typical successional trajectories
Self-replacement of black spruce

Asexual regeneration of understory

Little compositional change after disturbance

Typical successional trajectories
deep burning fires can shift successional trajectories
Deep burning fires can shift successional trajectories

Is there a threshold of organic soil consumption that has predictable effects on regeneration pathways?

recruitment declines with organic depth
Recruitment declines with organic depth

2-yr recruitment from seeding experiments (Alaska/Yukon)

n=4 to 16 (total plots = 60)

species differences lead to strong effects on post fire dominance

Seedling Density

Species differences lead to strong effects on post-fire dominance

Aboveground Biomass

  • Burned spruce forest
  • Alaska 40,000 ha burn
  • 8 yrs post-fire
  • n=19 stands
can we detect thresholds across real landscapes
Can we detect thresholds across real landscapes?
  • Alaska 2004 fires
  • 3 fire complexes
  • 90 black spruce sites
slide9

Regression Tree

pseudo-R2=0.65

Deciduous vs. Spruce Recruitment

Natural seedling densities 2 yrs post-fire

fire regeneration thresholds
Fire & regeneration thresholds
  • Residual organic layer determines seedbed quality
  • Differences in species sensitivity lead to strong composition effects
  • Increased fire severity => crossing threshold of residual organics => shift in successional trajectory
disturbance climate interact to alter black spruce resilience

directional change

tundra

black spruce

deciduous

Disturbance & climate interact to alter black spruce resilience

dynamic equilibrium

resilience feedbacks14

Low nutrient cycling

X

X

Conservative growth

Resilience Feedbacks

Species dominant

Organic seedbeds

X

Interactions

Recruitment

Mosses accumulate

critical research
Critical Research
  • Moving deeper in time
    • What are the longer term consequences of variations in fire severity?
  • Understanding space
    • Which parts of the landscape are vulnerable to shifts in trajectories, and which aren’t?
  • Can we test anticipated changes?
climate response dynamics
Climate response dynamics
  • Key feedbacks support resilience
  • Do threshold responses measure the depth of resilience?
  • At the landscape scale, is this the primary pathway for climate change response?