Carbon cycling feedbacks to climate

Transcription

1 Carbon cycling feedbacks to climate Ecosystem Function and Structure Successional Pathways Climate Feedbacks Climate Variability and Change Climate-Disturbance Interactions (Section II) (Section III) Regional Ecosystem Change Disturbance Regimes (spatial scale, temporal scale, severity) (Section IV) Coupled Social Ecological Systems

2 Climate-fire interactions Section I Climate Warming H2a: Climate-Fire Interactions D2 Changing Fire Regimes Section III Climate Feedbacks Seedling Establishment & Species Interactions D1 D3 Vegetation Composition & Successional Trajectory D4 NPP, Ecosystem Structure, Biogeochemical Cycling Section I Landscape Structure H2c H2b Ecosystem Services Pest-Herbivore-Climate Interactions Permafrost-Climate Interactions Section IV

3 Climate-fire interactions Section I Climate Warming H2a: Climate-Fire Interactions D2 Changing Fire Regimes Section III Climate Feedbacks Seedling Establishment & Species Interactions D1 D3 Vegetation Composition & Successional Trajectory D4 NPP, Ecosystem Structure, Biogeochemical Cycling Section I Landscape Structure H2c H2b Ecosystem Services Pest-Herbivore-Climate Interactions Permafrost-Climate Interactions Section IV

4 Climate-fire-permafrost interactions Section I Climate Warming H2a: Climate-Fire Interactions D2 Changing Fire Regimes Section III Climate Feedbacks Seedling Establishment & Species Interactions D1 D3 Vegetation Composition & Successional Trajectory D4 NPP, Ecosystem Structure, Biogeochemical Cycling Section I Landscape Structure H2c H2b Ecosystem Services Pest-Herbivore-Climate Interactions Permafrost-Climate Interactions Section IV

5 How will a more deciduous landscape function

6 What is next? Cross-scale interactions and landscape resilience Legacy locks and legacy links 1. Do deeper burns release legacy carbon? 2. How do unburned kipukas affect dynamics of regeneration and future fires? 3. Where and when does seed limitation drive patterns of tree establishment and succession? 4. Where and when does mycobiont limitation drive patterns of community assembly? 5. Can herbivores shift successional trajectories? 6

7 What is next? Cross-scale interactions and landscape resilience Legacy locks and legacy links 1. How does permafrost play into successional trajectories? 2. When successional trajectories shift, how does permafrost C loss compare to deciduous C gain? 3. What is the fate of permafrost N and how does it contribute to extant productivity? 4. How will terrestrial-aquatic linkages change in a more deciduous landscape? 1. Will changes in composition and age structure increase fire return interval in a warming climate? 7

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9 Carbon pool (gc m -2 ) Carbon pools over the disturbance cycle Carbon pool (gc m-2) t 0 Pre-fire (2004) t 1 Post-fire (2004) Chronosequences Spruce Spruce Spruce Deciduous Spruce Net C accumulation (tdeciduous 100 -t 1 ): Spruce 2877 g C m -2 Deciduous 7110 Years Years after after fire fire % legacy carbon at t 100 : Spruce 64 % Deciduous 28 NECB (t 100 -t 0 ): Spruce 375 g C m -2 Deciduous 3,233

10 Results: Spruce Deciduous [CO 2 ] T - * * Soil C < Plant C Fire - NECB Soil C,N Deciduous trees

11 ? Atmospheric CO 2 Regional Warming Net Ecosystem Carbon Balance - Heterotrophic Respiration & Other C Losses Rhizosphere C, N, O 2 NPP N Availability Permafrost Thaw Permafrost SOM Decomposition - Saturation

12 ALT (m) Permafrost response to depth of burning Stable climate Changing climate Romanvosky et al. in progress 12

13 Stream chemistry response to fire, permafrost Deepening of the active layer could drive sustained release of nitrate. Betts and Jones 2009, Harms and Jones 2012

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17 What s next? What have we learned? Fire regimes are intensifying in black spruce forest and tundra Area burned is increasing Bigger burns are deeper burns Intensity may be unique in paleo-record What new questions are emerging? Spatial heterogenaity within fires Linking current depth of burning to historic burning Landscape flammability feedbacks (demography, composition)

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19 Nitrogen pool (gn m -2 ) Nitrogen pools over the disturbance cycle Nitrogen pool (gn m-2) Spruce Net N accumulation (t Deciduous 100 -t 1 ): Spruce 70 g N m -2 Deciduous 110 Acquisition of deep permafrost N? Years Years after after fire fire % legacy N at t 100 : Spruce 70% Deciduous 35 Moss-associated N fixation? Spruce Spruce Spruce Deciduous NENB (t 100 -t 0 ): Spruce -0.8 g N m -2 Deciduous -6.8

20 C:N ratio over the disturbance cycle Spruce Deciduous 70 C:N ratio Spruce Spruce Spruce Deciduous Years after fire

21 Summary NECB was an order of magnitude greater in spruce deciduous than in spruce spruce Spruce spruce harbored twice as much legacy C and N as spruce deciduous Over both trajectories, N pools were resilient, recovering to pre-fire pool sizes by 100 years Change in species composition catalyzed transfer of N from low C:N soil organic matter to high C:N trees, resulting in greater ecosystem N use efficiency

22 Stabilizing feedbacks that maintain trajectories Low vascular NPP Slow nutrient turnover High moss NPP Slow decomposition Thick organic layer Cool, moist soils Long fire-free interval (succession) Low severity fire High severity fire Bryospheric feedbacks! Thin organic layer Warm, dry soils Low moss NPP Fast decomposition High vascular growth and litter production Fast nutrient turnover

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24 Hypothesis: Spruce Deciduous [CO 2 ] T Soil C > Plant C Fire - NECB Soil C,N Deciduous trees

25 Results: Spruce Deciduous [CO 2 ] T - * * Soil C < Plant C Fire - NECB Soil C,N Deciduous trees

26 Acknowledgements Students and postdocs Heather Alexander April Melvin Leslie Boby Melanie Jean Xanthe Walker Collaborators Jill Johnstone Terry Chapin Teresa Hollingsworth Scott Goetz Roger Ruess Syndonia Bret-Harte Ted Schuur Field and lab assistants Camilo Mojica Kamala Earl Julia Reiskind Grace Crummer Samantha Miller Funders NSF via BNZ and ARC LTER, JFSP, NASA, DOD

27 A deciduous tipping point in boreal forest? Mann, Rupp et al. 2012

28 C Pool (g C m-2) cm cm cm 5-10 cm 0-5 cm Carbon stocks and age in burned and unburned profiles at Willow Creek Age (years) Stand age Unburned Burned 5 Unburned profile Burned profile State Depth (cm) Age vs Depth

29 Post-fire SOL C (gc m -2 ) Residual SOL-C pools and successional Spruce Spruce Spruce Mixed Spruce Deciduous trajectory 1:1 Trajectories in year 10: Spruce = 30 Mixed = 17 Deciduous = 35 [0 trees = 8] 2000 Mean depth ~ 9cm Pre-fire SOL C (gc m -2 )