Phenology Modulates Carbon and Water Exchange of Ecosystems

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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 2006 B19, Land Surface Phenology, Seasonality
and Water Cycle
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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

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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
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Phenology Affects Evaporation, which affects
Atmospheric Demand, and Vice Versa
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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
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Spring Temperature Affects Phenology and the
Seasonality of CO2 Exchange case 1, Deciduous
Forests
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Phenology Modulates Source-Sink via LAI
Walker Branch Watershed, TN

• Interannual Variability in Length of Growing
  Season gt 30 days
• Latitudinal Variation in Length of Growing Season
  gt 30 days

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Spatial GradientsNEE and Length of Growing
Season
Baldocchi et al, 2001, BAMS
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Year to Year differences in NEE across sites is
due to differences in Growing Season Length
Baldocchi et al, 2001 Ecol Modelling
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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

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The Duration of Winter/Spring Rain affects
Phenology and the Seasonality of CO2 Exchange
case 2, Annual Grasslands
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Length of Rain Period affects Phenology of Annual
Grassland
Interannual variation of Wet season can vary by gt
50 days
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Timing of Rainfall Can Force Substantial
Interannual Variability in LAI
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Remote Sensing Can be Used to study Phenology of
Carbon Fluxes
Land Surface Water Index LSWI (?860 -
?1640)/(?860 ?1640)
PRI (r531 - r570) / (r531 r570)
PRI and NEE
Falk, Baldocchi, Ma, in preparation
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Humidity Deficits and PhenologyAnnual grassland
near Ione California

• Xu and Baldocchi, 2003 AgForMet

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Amount of Rain During the Wet Season Affects NEE
of Annual CA Grassland and Savanna Woodland
Ma, Baldocchi, Xu and Hehn, submitted, AgForMet
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Seasonality of Model Parameterse.g.
Photosynthetic Capacity
Live Fast, Die Young In Stressed Environments
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Annual and Spatial Variation in Photosynthetic
Capacity, Vcmax, for Deciduous Forests in North
America (HV, WB) and Europe (HE)
Wang et al, 2006 GCB
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Interannual Variation in Ps Capacity
Wang et al, 2006 GCB
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Seasonality of Vcmax is needed to simulate LE, H
and NEE
Wang et al, 2006 GCB
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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
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Effect of Timing of Leaf-Out on Evaporation,
Theory
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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
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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
  photosynthesisThus warming does not necessarily
  lead to higher CO2 uptake
• Angert et al, 2005, PNAS

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Phenology and PBL Growth
Deeper PBL Growth occurred after Leaf Out
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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
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Using the Onset of Photosynthesis as indicator of
Phenology
Baldocchi et al., 2005, Int J Biomet
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Soil Temperature An Objective Indicator of
Phenology??
Data of Pilegaard et al.
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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
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Onset of Spring is Delayed 5 days with each
degree reduction in mean temperature
Baldocchi et al. Int J. Biomet, 2005
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When Transformed onto a Climate Map, We observe a
General Correspondence with N-S gradient Obtained
from the denser Phenology Network
d140
d90
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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,

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Acknowledgements

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