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Phenology Modulates Carbon and Water Exchange of Ecosystems Dennis Baldocchi Siyan Ma Ecosystem Sciences Div/ESPM University of California, Berkeley AGU.

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Presentation on theme: "Phenology Modulates Carbon and Water Exchange of Ecosystems Dennis Baldocchi Siyan Ma Ecosystem Sciences Div/ESPM University of California, Berkeley AGU."— Presentation transcript:

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

6 Spring Temperature Affects Phenology and the Seasonality of CO 2 Exchange: case 1, Deciduous Forests

7 Walker Branch Watershed, TN Phenology Modulates Source-Sink via LAI 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 CO 2 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 PRI and NEE Land Surface Water Index LSWI = (ρ860 - ρ1640)/(ρ860 + ρ1640) PRI = ( ) / ( ) 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 Wang et al, 2006 GCB Annual and Spatial Variation in Photosynthetic Capacity, Vcmax, for Deciduous Forests in North America (HV, WB) and Europe (HE)

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

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

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 R g (5.43 vs 5.41 GJ m -2 ) and T air (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 CO 2 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 CO 2 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 Data of Pilegaard et al. Soil Temperature: An Objective Indicator of Phenology??

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

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

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

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


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