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 well drained moderately drained poorly drained b. Pre-fire organic layer depth high resilience c. Propagation potential of smouldering combustion d. Magnitude of severity effects high resilience low resilience (+) (-) 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