Scott Saleska (U. of Arizona)

1. From source to sink: Tracing the effects of natural disturbance on tropical forest carbon balance Scott Saleska (U. of Arizona) Lucy Hutyra, Elizabeth Hammond-Pyle, Dan Curran, Bill Munger, Greg Santoni, Steve Wofsy(Harvard University) Kadson Oliveira (LBA-Santarem) Simone Vieira, Plinio Camargo (CENA, U. of São Paulo)

2. How do we estimate large-scale carbon balance?

3. How do we estimate large-scale carbon balance (given that disturbance is intrinsic to old-growth forest dynamics)?

4. How do we estimate large-scale carbon balance (given that disturbance is intrinsic to old-growth forest dynamics)? • Introduction: Two sub-questions • Prior findings from an eddy flux study: disturbance-induced carbon loss in old-growth forest? • A preliminary test of predictions from prior findings • Conclusion: Understanding disturbance

5. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 Mg (C) ha-1 yr-1 0 NEP (net ecosystem productivity) = NPP - Rhet -10 -20 Forest Gap Age (time since disturbance in years) Introduction: Modeled carbon flux following disturbance in gap of “balanced-biosphere” Amazon rainforest Positive NEP (=sink atm CO2) Negative NEP (=source to atm) 0 20 40 60 80 Source: Moorcroft, Hurtt, & Pacala (2001)

6. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 NEP (net ecosystem productivity) = NPP - Rhet -10 -20 Introduction: Modeled carbon flux following disturbance in gap of “balanced-biosphere” Amazon rainforest Key point: • Landscape in carbon balance, but… • Individual gaps may never be in carbon balance Mg (C) ha-1 yr-1 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

7. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 NEP (net ecosystem productivity) = NPP - Rhet -10 -20 What is large-scale Carbon balance?Two sub-questions: • What is the distribution of gap ages across the landscape? • What are the detailed dynamics of forest response to disturbance? Mg (C) ha-1 yr-1 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

8. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 NEP (net ecosystem productivity) = NPP - Rhet -10 -20 What is large-scale Carbon balance?Two sub-questions: • What is the distribution of gap ages across the landscape? • What are the detailed dynamics of forest response to disturbance? Mg (C) ha-1 yr-1 (see Jeff Chambers talk coming up…) 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

9. LBA project near Santarem: Controls on Carbon Balance in the Tapajós National Forest, Brazil Rio Amazonas Santarém Rio Tapajós Km 67 site Km 83 site

10. Profile systeminlets (8 levels) Methods • Eddy Flux: 64m tall tower at Km67 in Tapajos forest • Biometry: ~3000 trees and dead wood measured in 20 ha in footprint of eddy tower 58 m: Eddy flux

11. Prior findings 1: eddy flux measurement show net loss of C in Tapajos National forest of Amazônia, Average Annual C- Balance 6 5 4 3 2 1 0 -1 -2 loss to atmosphere Accumulated Mg(C) ha-1 uptake Source: Saleska et al. (2003) Science 2001 2002 2003

12. 4 recruit 2 growth mortality 0 decomp-osition mortality -2 -4 -6 Prior findings 2: Carbon fluxes to biomass and dead wood  suggests C-loss is transient consequence of disturbance Two observations suggest disturbance-recovery process:(1) The balance for live wood and dead wood is in opposite directions live wood change: +1.4  0.6 MgC ha-1 yr-1 dead wood change: -3.3  1.1 (loss) whole-forestnet:-1.9 1.0 (loss) net C loss |net C uptake growth/loss rate (Mg C ha-1 yr-1) Live Biomass(145-160 MgC/ha) Dead Wood(30–45 MgC/ha)

13. loss to atmosphere Recruitment Net Accumulation(1.4 Mg C ha-1yr-1) Growth uptake Mortality Outgrowth 10 35 60 85 110 135 160 Prior findings 2: Carbon fluxes to biomass by size-class  suggests C-loss is transient consequence of disturbance 3 • Observation 2: • Demographic shift: • The increase in flux to biomass isin the smaller size classes • Corresponding increase in density of tree stems in the smaller size classes 2 1 flux, MgC ha-1yr-1 0 -1 -2 size class, cm DBH

14. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 -10 -20 Predictions for continued observations following disturbance (1) What is the distribution of gap ages across the landscape? (2) What are the detailed dynamics of forest response to disturbance? Mg (C) ha-1 yr-1 NEP (net ecosystem productivity) = NPP - Rhet 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

15. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 -10 -20 Predictions for continued observations following disturbance (1) What is the distribution of gap ages across the landscape? (2) What are the detailed dynamics of forest response to disturbance? Mg (C) ha-1 yr-1 NEP (net ecosystem productivity) = NPP - Rhet Tapajos Km 67 site?(loss) 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

16. NPP (net primary productivity) 20 Rhet (heterotrophic respiration) 10 0 -10 -20 Predictions for continued observations following disturbance Mg (C) ha-1 yr-1 NEP (net ecosystem productivity) = NPP - Rhet Tapajos Km 67 site?(loss) 0 20 40 60 80 Forest Gap Age (time since disturbance in years)

17. Predictions for continued observations following disturbance Rhet (respiration) (1) Whole-Ecosystem flux Predictions (a) NEP should move from source to sink NPP Mg (C) ha yr-1 Positive NEP (=sink) Negative NEP (=source) NEP (net ecosystem productivity) = NPP - Rhet

18. Predictions for continued observations following disturbance Rhet (respiration) (1) Whole-Ecosystem flux Predictions (a) NEP should move from source to sink (b) Due to decline in respiration (as deadwood substrate decays away) NPP Mg (C) ha yr-1 Positive NEP (=sink) Negative NEP (=source) NEP (net ecosystem productivity) = NPP - Rhet

19. Predictions for continued observations following disturbance recruit growth Mort. De-comp. Mort. 4 2 0 -2 -4 Live Biomass Dead Wood (2) Forest Demography Predictions (a) Shift from uptake towards balance in live biomass (i.e. decrease in growth/ recruitment, increase in mortality) prediction (a) net C loss |net C uptake growth/loss rate

20. Predictions for continued observations following disturbance recruit growth Mort. De-comp. Mort. 4 2 0 -2 -4 Live Biomass Dead Wood (2) Forest Demography Predictions (a) Shift from uptake towards balance in live biomass (i.e. decrease in growth/ recruitment, increase in mortality) (b) Shift from loss towards balance in dead wood prediction (a) (b) net C loss |net C uptake growth/loss rate

21. Predictions for continued observations following disturbance 3 recruit 2 growth Mort. 1 De-comp. Mort. 4 0 2 -1 0 -2 -2 -4 Live Biomass Dead Wood (2) Forest Demography Predictions (a) Shift from uptake towards balance in live biomass (i.e. decrease in growth/ recruitment, increase in mortality) (b) Shift from loss towards balance in dead wood (c) Shift in tree growth from smaller to middle size classes prediction (a) (b) net C loss |net C uptake growth/loss rate (c) Tree Size-class

22. III. Test of predictions with new observations

23. loss to atmosphere uptake Test of predictionsCumulative km67 Carbon Flux, 2001-2005 source Mg (C) ha-1 -3 -2 -1 0 1 2 3 4 5 Jan Jul 2001 2002 2003 2004 2005

24. loss to atmosphere uptake Test of predictionsCumulative km67 Carbon Flux, 2001-2005 source sink Mg (C) ha-1 -3 -2 -1 0 1 2 3 4 5 Jan Jul 2001 2002 2003 2004 2005

25. loss to atmosphere uptake Test of predictionsCumulative km67 Carbon Flux, 2001-2005 2002 Cumulative Mg (C) ha-1 2005 2003 2004 Day of Year

26. Test of predictions:Trends in Annual sums of carbon flux Resp (declining at 0.9 MgC/ha/yr2) Component fluxes(MgC/ha/yr) GPP (increasing at 0.6 MgC/ha/yr2) Net Exchange (loss) (= Resp – GPP)(MgC/ha/yr)

27. Precip controls short-term, but not long-term, integrated Resp flux Annual resp vs precip Monthly resp vs precip 2002 2003 Respiration (MgC/ha/yr) 2004 Resp = 29.2 + 0.02(±.003)·Precip (R2 = 0.5) Monthly precip (mm/month) Annual precip (mm/year)

28. Test of predictions: Forest Demography (a): Live biomass pool shifts toward balance Carbon fluxes to Live Biomass at km 67 6 Recruitment Growth Mortality 0.85 Net Uptake 0.45 4 1.68 2 0.59 3.24 3.16 net C loss |net C uptake MgC / ha / yr 0 Net Uptake Net Uptake(near zero) -2 -2.41 -3.02 -4 1999 - 2001 2001 - 2005

29. 2.0 1.5 1.0 0.5 0.0 10 35 60 85 110 135 160 Test of predictions: Forest Demography (c): “Grow-in” shifts tree growth from smaller to larger size-classes annual growth increment (MgC) by size class 1999-2001 2001-2005 MgC/ha/year Size-class (cm DBH) 0.05 1999-2001 2001-2005 0.03 MgC growth/ MgC live 0.01 0.0 10-35 35-60 60-85 85-110 110-135 135-160 160-185 size class, cm DBH

30. Summary Preliminary pattern confirms disturbance recovery hypothesis: (1) for eddy flux predictions: • Net ecosystem exchange shifts from source towards sink • Due in part to decline in ecosystem respiration (2) for demographic predictions: • Live biomass pool shifts towards balance • Grow-in shifts growth fluxes towards larger size classes

31. IV. Conclusions • Multiple measures (demography, component fluxes, net C-balance) can be integrated to detect and track whole-forest response to disturbance • Detailed quantification of: - Flux magnitudes & Response times- demographic stateallows tests of models of important forest dynamics • We are making progress on understanding key factors for predicting large-scale forest carbon balance

33. Aboveground Biomass timeseries in 0.5-ha plots of Linhares Atlantic rainforest Large-impact ENSO events Rolim et al. (2005)