Phenology Modulates Carbon and Water Exchange of Ecosystems

1. Phenology Modulates Carbon and Water Exchange of Ecosystems Dennis Baldocchi Siyan Ma Ecosystem Sciences Div/ESPM University of California, Berkeley AGU 2006 B19, Land Surface Phenology, Seasonality and Water Cycle

2. Objectives • Phenology and Vegetation-Atmosphere Interactions • Role of Phenology on Carbon and Water Fluxes • Leaf Area Index, LAI • Photosynthetic Capacity, Vcmax • Annual Carbon Fluxes • Annual Evaporation • PBL Dynamics • New Assessment of Phenology • Temperature Deciduous Forest • When Soil Temperature Exceeds Mean Annual Air Temperature • Annual Grassland • Amount of Rainfall in the Spring

3. Hopkins Law of Phenology • Phenology differs by four days for every degree of latitude, every 5 degrees of latitude and every 400 feet of altitude • . Andrew Delmar Hopkins Schwartz, M. D., 1997. Spring Index Models: An Approach to Connecting Satellite and Surface Phenology. In Phenology of Seasonal Climates

4. Phenology Affects Evaporation, which affects Atmospheric Demand, and Vice Versa

5. Phenology, a Measure of Global Change Mean annual growing season in Europe increases by 10.8 days from 1981 to 1991. Menzel and Fabian, Nature 1999

6. Spring Temperature Affects Phenology and the Seasonality of CO2 Exchange: case 1, Deciduous Forests

7. Phenology Modulates Source-Sink via LAI Walker Branch Watershed, TN • Interannual Variability in Length of Growing Season > 30 days • Latitudinal Variation in Length of Growing Season > 30 days

8. Spatial Gradients:NEE and Length of Growing Season Baldocchi et al, 2001, BAMS

9. Year to Year differences in NEE across sites is due to differences in Growing Season Length Baldocchi et al, 2001 Ecol Modelling

10. Caveat Emptor • Growing Season Length has More Explanatory Power across a Latitudinal Gradient than at an Individual Site • Additional factors explaining annual NEE at a Single Site include: • Absence/presence winter snow • Occurrence of Summer Drought • Extent of cloudiness

11. The Duration of Winter/Spring Rain affects Phenology and the Seasonality of CO2 Exchange: case 2, Annual Grasslands

12. Length of Rain Period affects Phenology of Annual Grassland Interannual variation of Wet season can vary by > 50 days

13. Timing of Rainfall Can Force Substantial Interannual Variability in LAI

14. Remote Sensing Can be Used to study Phenology of Carbon Fluxes Land Surface Water Index LSWI = (ρ860 - ρ1640)/(ρ860 + ρ1640) PRI = (r531 - r570) / (r531 + r570) PRI and NEE Falk, Baldocchi, Ma, in preparation

15. Humidity Deficits and Phenology:Annual grassland near Ione California Xu and Baldocchi, 2003 AgForMet

16. Amount of Rain During the Wet Season Affects NEE of Annual CA Grassland and Savanna Woodland Ma, Baldocchi, Xu and Hehn, submitted, AgForMet

17. Seasonality of Model Parameters:e.g. Photosynthetic Capacity Live Fast, Die Young In Stressed Environments

18. Annual and Spatial Variation in Photosynthetic Capacity, Vcmax, for Deciduous Forests in North America (HV, WB) and Europe (HE) Wang et al, 2006 GCB

19. Interannual Variation in Ps Capacity Wang et al, 2006 GCB

20. Seasonality of Vcmax is needed to simulate LE, H and NEE Wang et al, 2006 GCB

21. Growing Season Length and ET, Field Data Year with Longer Growing Season (13 days) Evaporated More (27 mm). Other Climate Factors could have confounded results, but Rg (5.43 vs 5.41 GJ m-2) and Tair (14.5 vs 14.9 C) were similar and rainfall was ample (1682 vs 1435 mm) Wilson and Baldocchi, 2000, AgForMet

22. Effect of Timing of Leaf-Out on Evaporation, Theory

23. Year to Year differences in LE is partly due to differences in Growing Season Length Field data show that ET decreases by 2.07 mm for each day the start of the growing season is delayed

24. Caveat Emptor • Early Spring can be followed by Summer Drought • ‘Net spring CO2 uptake increased from 1994-2002, whereas net growing season uptake did not... We have shown that these opposing trends in summer and spring are probably related to a drought-induced reduction in summer photosynthesis…Thus warming does not necessarily lead to higher CO2 uptake’ • Angert et al, 2005, PNAS

25. Phenology and PBL Growth Deeper PBL Growth occurred after Leaf Out

26. Predicting Phenology • Growing Degree Days • Chill Degree Days • Chill Hours • Chill Degree Hours • Heat Degree Days Critical Heat Units Need Calibration and are not Universal

27. Using the Onset of Photosynthesis as indicator of Phenology Baldocchi et al., 2005, Int J Biomet

28. Soil Temperature: An Objective Indicator of Phenology?? Data of Pilegaard et al.

29. Soil Temperature: An Objective Measure of Phenology, part 2 Data of: Baldocchi, Wofsy, Pilegaard, Curtis, Black, Fuentes, Valentini, Knohl, Yamamoto. Granier, Schmid Baldocchi et al. Int J. Biomet, 2005

30. Onset of Spring is Delayed ~ 5 days with each degree reduction in mean temperature Baldocchi et al. Int J. Biomet, 2005

31. When Transformed onto a Climate Map, We observe a General Correspondence with N-S gradient Obtained from the denser Phenology Network d140 d90

32. Summary and Conclusions • The Length of the Growing Season has significant effects on annual Carbon and Water exchange • As long as Warmer Springs are not followed by Summer Drought • The correspondence between soil temperature and mean annual air temperature has a strong correlation with Spring Leaf-out • The metric does not need tuning/calibration and works across a wide latitudinal range. • Processes derived from Networks of Flux Measurement Sites can be Transformed onto Climate Space to produce Phenology Maps • New Technologies for monitoring Phenology • Eddy Flux, $$$$ • Digital Camera, $$ • LED, NDVI/PRI Sensor, $

33. Acknowledgements • Funding • DOE/TCP, NIGEC/WESTGEC, CalAgExpt Station • Collaborators • YingPing Wang • Matthias Falk • Liukang Xu • Kell Wilson • AmeriFlux/Fluxnet Colleagues