1. What have we learned from forest tower flux data following disturbance? Brian Amiro, A. Barr, J. Barr, T.A. Black, R. Bracho, M. Brown, J. Chen, K. Clark, K. Davis, A. Desai, S. Dore, V. Engel, J. Fuentes, A. Goldstein, M. Goulden, T. Kolb, M. Lavigne, B. Law, H. Margolis, T. Martin, J.H. McCaughey, M. Montes-Helu, A. Noormets, J. Randerson, G. Starr, J. Xiao

2. Disturbances in North American Forests (total area 7 million km 2 ) Fire: 40,000 km 2 /year Harvest: 50,000 km 2 /year Insects: larger Storms/hurricanes: > 17,000 km 2 /year Disease: ???

3. Disturbance Sequence Studies Our goal: Synthesize flux tower measurements of CO 2 exchange for experiments designed to understand the effect of disturbance Chronosequence approach: forests of different ages Time series approach: follow a single site through a disturbance cycle JGR 115: G00K02, doi:10.1029/2010JG001390, 2010 Acknowledgements: Large host of contributors and funders

4. Disturbance Chronosequences with Annual NEP measured by eddy covariance Fire = 4 Harvest = 7+ Insects = 3 Hurricane Wilma

5. Fire Sites: Boreal and Arizona

6. Forest Tent Caterpillar Mountain Pine Beetle Gypsy Moth INSECTS

7. Harvesting: Practices highly variable. Clearcut, thinning…

8. Hurricane Wilma in October 2005; destroyed 30% of trees at a Florida mangrove site Trajectory of hurricane Wilma during October 2005

9. Annual Carbon Flux from Eddy Covariance Towers Measure CO 2 directly using fast- response anemometer and gas analyser Get 30-min mean fluxes Calculate annual NEP (Net Ecosystem Production) Calculate GPP (Gross Photosynthetic Production) and ER (Ecosystem Respiration) from tower data Networks: Ameriflux, Fluxnet- Canada (Canadian Carbon Program)

10. Annual NEP for fire chronosequences: boreal sites gaining carbon after 10 years

11. Fire: GPP and ER ER relatively flat with age at boreal sites

12. Time to recovery from fire? Curve fit of NEP data from boreal fire sites Typical range of mean carbon lost through combustion

13. Harvest Chronosequences: NEP

14. Harvest GPP and ER

15. Are there any relationships that apply with age following stand-replacing disturbance? Leaf area index (LAI) development? What about GPP and ER relationships?

16. Ratio GPP/ER with age Asymptote = 1.23 Ra = 0.55*GPP

17. Heterotrophic Respiration (normalized to mean for individual chronosequences) assuming Ra = 0.55*GPP No statistically significant pattern with age

18. NEP Thinning: Harvest and Hurricane

19. Insect sequences: NEP CFS web page

20. What have we observed? Forests become carbon sinks within 5 to 20 years following stand-replacing events GEP/ER ratio becomes relatively constant by 15 years Heterotrophic respiration variable with no strong age function Quick recovery in NEP following thinning Insect effects variable: depends on nature of infestation, but NEP becomes positive quickly

21. What should we do; where are the gaps? All sites were disturbed at some time, so when does the disturbance history become less important than inter-annual variability and other site factors? Do young sites respond to climate and stressors differently from more mature sites? Do we need more chronosequences? Where? For how long? Can we compare severity/management practices?