Controls of carbon budgets in terrestrial ecosystems
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Controls of carbon budgets in terrestrial ecosystems Does carbon storage in terrestrial ecosystems really depend on temperature? What factors do we need to consider when we assess vegetation — atmosphere coupling in climate change scenarios?

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Controls of carbon budgets in terrestrial ecosystems

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Controls of carbon budgets in terrestrial ecosystems

  • Controls of carbon budgets in terrestrial ecosystems

  • Does carbon storage in terrestrial ecosystems really depend on temperature?

  • What factors do we need to consider when we assess vegetation—atmosphere coupling in climate change scenarios?

  • How well do coupled climate—vegetation models simulate the response of forest CO2 fluxes and carbon sequestration to variations in temperature?

  • What controls the long-term storage of organic carbon in boreal soils ? [current content: 200—400 ppm of CO2 ; all soils, > 700 ppm ]

  • Steven C. Wofsy, Harvard University

  • Presented at: ICDC7 Boulder, CO, 29 Sep 2005


Controls of carbon budgets in terrestrial ecosystems

120

100

80

R

60

40

20

0

-20

-10

0

10

20

30

T oC

  • “Land carbon storage depends on the balance between the input of carbon as Net Primary Productivity (NPP), and the loss of carbon as heterotrophic (soil) respiration (Rh).”

  • NPP modeled as dependent on light, nutrients, precipitation

  • Rh modeled as a function of T. Is this right?

Daily Mean Ecosystem Respiration (mmole/m2/s) vs T (C) Photosynthesis vs sunlight

Harvard Forest

Exp fit


Controls of carbon budgets in terrestrial ecosystems

Modeling long-term Net Ecosystem Carbon Production (NEP)(1st-order):

“tree”

solar

Atmosphere

CO2, H2O

Leaves (P, R6)

H2O, nutrients

CO2

Org C

Boles (R5)

Org C

Roots (R4)

Soils R1 R2 R3


Controls of carbon budgets in terrestrial ecosystems

Do climate—ecosystem models capture the temperature dependence of carbon storage? Or the long-term trends in C storage?

Example 1: a typical mid-latitude forest (Harvard Forest, Central New England; agricultural use 1750-1850).

60-80 year old mixed deciduous forest, with CO2 fluxes to/from the atmosphere measured every half hour, for 15 years (1991-2005) (S. Wofsy, J. W. Munger, B. Daube, M. Goulden, C. Barford, S. Urbanski, many others), plus a soil warming manipulation (J. Melillo, K. Nadelhofer, P. Studler).


Controls of carbon budgets in terrestrial ecosystems

Model (IBIS) vs. Observed C balance at a transition deciduous forest.

Errors in both seasons are due to T driving respiration

emission

uptake

phenology

R vs T: fundamental to climate change—the mean is right, but the model is never right in any month and the CO2 Flux–T feedback is wrong!


Controls of carbon budgets in terrestrial ecosystems

Modeled and observed respiration at Harvard Forest


Controls of carbon budgets in terrestrial ecosystems

“Overall, warming treatment did not significantly change soil respiration either with or without clipping.” (Luo et al., 2001)


Controls of carbon budgets in terrestrial ecosystems

Annual change (%) in soil respiration due to 5o soil warming over a thirteen-year period at Harvard Forest [Melillo, Nadelhofer, Studler, et al. –Marine Biological Laboratory, Woods Hole, MA].


Controls of carbon budgets in terrestrial ecosystems

Does this extra N increase enhance tree growth?

Annual change (%) in N mineralization due to soil warming over a thirteen-year period at Harvard Forest [Melillo, Nadelhofer, Studler, et al. –Marine Biological Laboratory, Woods Hole, MA].


Controls of carbon budgets in terrestrial ecosystems

  • Accel. G, R

  • Accel. NEE

  • Higher LUE

Year

1992

1994

1996

1998

2000

2002

-16

uptake

NEElight sat’d

16

R

-18

-1x

GEE

mean NEE PAR 1200-1500 (mmole/sq. m/yr)

14

emission

-20

R (tonC/ha/yr)

12

-22

More efficient

1992

1994

1996

1998

2000

2002

10

Year

1992

1994

1996

1998

2000

2002

2004

Year

0

NEE

Harvard Forest

AmeriFlux Data: 1991--2004

-1

-2

NEE (tonC/ha/yr)

-3

AGWB

incr. rate net uptake

-4

1992

1994

1996

1998

2000

2002

2004

Long-term changes at Harvard Forest J. W. Munger, S. Urbanski, S. C. Wofsy et al.


Controls of carbon budgets in terrestrial ecosystems

20 30 50 cm

Example 2: Climate and C at a Boreal Forest (NOBS) flux site, Thompson, MB

PEAT

45% cover

Jan

Snow cover

Temperature (rapid warming)

1970

2000

1900

2000

Jul


Controls of carbon budgets in terrestrial ecosystems

a. NEE

b. T anomaly

c. CMI.3 anomaly

Boreal Forest: Comparison of (a) NEE, (b) temperature anomaly, (c) 3-year lagged climate moisture index anomaly (10 years of AmeriFlux Data)

Uptake | emission

Temperatures warm up, ecosystem switches: sourcesink


Controls of carbon budgets in terrestrial ecosystems

NEE: C balance at a bog: Jun—Sep

Daily respiration, g C m-2

Water table depth, cm

Water Table

Water Table Depth (cm) or T (c)

T

Summer 2002

Summer 2003

Summer 2004

Temper1ature, °C

R (gC m-2 day-1)


Controls of carbon budgets in terrestrial ecosystems

a. NEE

b. T anomaly

c. CMI.3 anomaly

Boreal Forest: Comparison of (a) NEE, (b) temperature anomaly, (c) 3-year lagged climate moisture index anomaly (10 years of AmeriFlux Data)

Uptake | emission

Water balance & (temperature) explain the transition: sourcesink


Correlation d t d soil moisture index ccsm1 carbon control simulation

Positive correlation  warmer-wetter; or cooler-drier

Negative correlation  warmer-drier; or cooler-wetter

Correlation: {DT, D soil moisture index}CCSM1-Carbon Control Simulation

DJF

JJA

slide courtesy Inez Fung [I. Fung, S. Doney, et al.]]


Controls of carbon budgets in terrestrial ecosystems

high T, high ppt

Low T, low ppt

Recent climate variations in central Canada have been [cold:dry] and [warm:wet] …


Controls of carbon budgets in terrestrial ecosystems

Holdridge Life Zones & potential vegetation: Mean T, Precip, and E/P control vegetation cover: warmer-drier leads to strong degradation in the tropics.

.25

125

Data courtesy of D. Skole

1.0

P

1.5

E/P

1500

T

6

8.0

8000

24

Holdridge life zones (Holdridge 1967)


Controls of carbon budgets in terrestrial ecosystems

Summary•How well do coupled climate—vegetation models simulate the response of forest CO2 fluxes and carbon sequestration to warming? Many models over-estimate the sensitivity of ecosystem C storage to T.•What controls the long-term storage of organic carbon in boreal soils ? [current content: 200—400 ppm of CO2 ; all soils, > 700 ppm equivalent]. Hydrological balance in concert with T dominate; if changed climate has warmer wetter covariance, boreal lands may actually increase C storage in a warmer world.


Controls of carbon budgets in terrestrial ecosystems

What did we learn?Coupled climate vegetation modeling must carefully and critically examine predictions for climate change and ecosystem response in terms of the key parameters (•regional T •Precipitation •Human impacts (ignition, agriculture, air pollution) and their •covariances .Consider advancing beyond the traditional focus on global mean T. These are all 1st order factors.


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