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
Coherent response among sites, impact of length of growing season. Does not account for interannual variability at a site, due to snow cover, drought, cloudy vs clear summers etc.
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. Year with Longer Growing Season (13 days) Evaporated More (27 mm).
Growing Season Length and ET, Field Data
Rg 5.43 vs 5.41 GJ; Tai 14.5 vs 14.9; ppt 1682 vs 1435
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 , 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. An Objective Indicator of Phenology??
Soil Temperature:
An Objective Indicator of Phenology??
Data of Pilegaard et al.

29. An Objective Measure of Phenology, part 2
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 Collaborators
DOE/TCP, NIGEC/WESTGEC, CalAgExpt Station
Collaborators
YingPing Wang
Matthias Falk
Liukang Xu
Kell Wilson
AmeriFlux/Fluxnet Colleagues