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C. Yi, K.J. Davis, The Penn State University P.S. Bakwin, NOAA/CMDL PowerPoint PPT Presentation


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The observed responses of ecosystem CO2 exchange to climate variation from diurnal to annual time scale in the northern America. C. Yi, K.J. Davis, The Penn State University P.S. Bakwin, NOAA/CMDL T. Zhou, Beijing Normal University D.D. Baldocchi and colleagues, UC Berkeley

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C. Yi, K.J. Davis, The Penn State University P.S. Bakwin, NOAA/CMDL

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The observed responses of ecosystem CO2 exchange to climate variation from diurnal to annual time scale in the northern America.

C. Yi, K.J. Davis, The Penn State University

P.S. Bakwin, NOAA/CMDL

T. Zhou, Beijing Normal University

D.D. Baldocchi and colleagues, UC Berkeley

S. Wofsy and colleagues, Harvard University


Interannual

variability

in the rate of

accumulation

of atmospheric

CO2


Issues

  • What climatic factors control the interannual variability in NEE?


Part I: Climate variables and NEE at various time scales(NB, WB, WL, HF)

Respiration and temperature

Correlation between nighttime tower flux and air temperature is very high on daily, monthly and seasonal time scales.

Correlation breaks down on interannual scales.


Respiration and temperature

Northern OBS tower (NB)

Manitoba, Canada

Wofsy, Munger et al.

Boreal black spruce forest


Respiration and

temperature

WLEF TV tower (WL)

Northern Wisconsin, USA

Davis, Bakwin et al.

Mixed forest/wetland mosaic


Respiration and

temperature

Harvard Forest (HF)

Massachusetts, USA

Wofsy, Munger et al.

Deciduous forest


Respiration and

temperature

Walker Branch tower (WB)

Baldocchi, Wilson et al.

Tennessee, USA

Deciduous forest


Why does the temperature-respiration relationship break down on annual time scales?

Hypotheses:

  • Annual respiration is proportional to annual litter production which is a weak function of temperature?

  • Temperature sensitivity is limited at the seasonal extremes (summer, winter).


Soil carbon pool

Soil respiration Litter production (Ta, P, Rn, fertilizer, …)


Respiration in autumn is much higher than in spring even though temperature is similar between these two seasons.


Season

NB

B R2T

WL

B R2T

HV

B R2T

WB

B R2T

Spring

0.0351 0.47 -5.1

0.0844 0.50 5.2

0.0445 0.38 5.1

0.0632 0.60 13.3

Summer

0.0676 0.36 13.3

0.0526 0.23 16.2

0.0255 0.08 17.0

0.0283 0.10 22.3

Autumn

0.0603 0.83 -1.3

0.0801 0.45 7.8

0.0231 0.18 8.0

0.0547 0.66 14.1

Winter

0.0126 0.08 -21.8

0.0142 0.04 -7.0

0.0283 0.08 -3.3

0.0340 0.46 4.4

Seasonal distribution of temperature sensitivity B, (Re=AeBT ).

Spring B is the largest except at the NB site.

There is no correlation between T and respiration in winter except at the WB site.


Climate variables and NEE at various time scales(NB, WB, WL, HF)

NEE of CO2 and precipitation

Correlation between NEE and precipitation is very poor on daily, monthly and seasonal time scales.

Correlation becomes strong for interannual time scales.


NEE and precipitation

Northern OBS tower (NB)

Manitoba, Canada

Wofsy, Munger et al.

Boreal black spruce forest


NEE and precipitation

WLEF TV tower (WL)

Northern Wisconsin, USA

Davis, Bakwin et al.

Mixed forest/wetland mosaic


NEE and precipitation

Harvard Forest (HF)

Massachusetts, USA

Wofsy, Munger et al.

Deciduous forest


NEE and precipitation

Walker Branch tower (WB)

Baldocchi, Wilson et al.

Tennessee, USA

Deciduous forest


Climate variables and NEE at various time scales(NB, WB, WL, HF)

NEE and net radiation

Correlation between NEE and net radiation is strong on all time scales.


NEE and net radiation

Northern OBS tower (NB)

Manitoba, Canada

Wofsy, Munger et al.

Boreal black spruce forest


NEE and net radiation

WLEF TV tower (WL)

Northern Wisconsin, USA

Davis, Bakwin et al.

Mixed forest/wetland mosaic


NEE and net radiation

Harvard Forest (HF)

Massachusetts, USA

Wofsy, Munger et al.

Deciduous forest


NEE and net radiation

Walker Branch tower (WB)

Baldocchi, Wilson et al.

Tennessee, USA

Deciduous forest


Climate variables and NEE at various time scales(NB, WB, WL, HF)

NEE and PAR

Correlation between NEE and PAR is good on short time scales, and becomes worse on annual time scale.


NEE and PAR

Northern OBS tower (NB)

Manitoba, Canada

Wofsy, Munger et al.

Boreal black spruce forest


NEE and PAR

WLEF TV tower (WL)

Northern Wisconsin, USA

Davis, Bakwin et al.

Mixed forest/wetland mosaic


NEE and PAR

Harvard Forest (HF)

Massachusetts, USA

Wofsy, Munger et al.

Deciduous forest


NEE and PAR

Walker Branch tower (WB)

Baldocchi, Wilson et al.

Tennessee, USA

Deciduous forest


Summary

  • Dependence of NEE on climatic factors is not consistent across time scales.

  • Net radiation and precipitation become more correlated with NEE on annual time scale.

  • Dryness=Rn/(L*P) may be used as an annual controlling parameter on interannual variability of NEE of CO2.


Discontinuous permafrost exists

Water stress is not critical

Soil thaw is critical; this depends on Rn

Drought leads to more release of CO2

With abundant soil moisture, available energy is critical for CO2 uptake.

As dryness>0.95, water stress becomes critical.

1998 is the second year of drought. 1999 is the third year of drought. (?)

Drought has strong effect on interannual variability in NEE at WB.

NB

WL

HV

WB


Across many sites

Average per site over several years

HV-Harvard Forest (US,92-99)

TH-Tharandt (Germany, 97-99)

WL-WLEF (US, 97-99)

WB-Walker Branch (US,95-98)

NO-Norunda (Sweden,96-97)

LW-Little Washita (US,97-98)

LO-Loobos (Netherlands,97-98)

HL-Howland (US, 96-97)

HE-Hesse (France, 98-99)


Acknowledgements

  • Funding and personnel support:

    • DoE – NIGEC – Midwest and Great Plains

    • NOAA CMDL

    • NASA – EOS Validation

    • DoE – TCP/TECO

    • NSF/NCAR

    • USDA-FS


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