Carbon dynamics: perspectives from ecosystem models
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Carbon dynamics: perspectives from ecosystem models
Sarah C. Davis
Interface Meeting, Captiva Island FlMarch 2, 2011
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Major challenges• Long-term responses to climate change• Effects of land use change
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Outline
• Approach to modeling• Carbon trends in perennial grass crops
– belowground carbon sequestration• Land use issues and challenges• Carbon dynamics in forested ecosystems
– aboveground carbon sequestration• Resolving long term responses of forests to
climate change
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Ecosystem modeling approach
• Comparative ecosystem physiology
• Comparative ecosystem biogeochemistry
• Coupled to hypothesis-driven research
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Maximumgross
photosynthesis
Leaf nitrogen content
Net
pho
tosy
nthe
sis
Basalrespiration
Realizedgross
photosynthesis
Realizedrespiration
Day temperatureNight temperature
Radiation PARdaylength
VPD
GPP
NPP
Example of a physiology-driven model(PnET)
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Example of biogeochemistry- driven model
Parton et al. 1998
Miscanthus x giganteus
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Above- vs. Below-ground Carbon Sinks
• “Judicious management” can increase soil C– Lugo et al., 1986, Cerri et al. 1991, Izaurralde et al.
2000, Conant et al. 2001, Zan et al. 2001, Lal 2004
• Long-term carbon sequestration more dependent on increasing aboveground biomass– Schlesinger 1990, Richter et al. 1999, Schlesinger and
Lichter 2001
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Ecosystem productivity
Ecos
yste
m p
rodu
ctivi
ty
Ecosystem Models
Atmospheric CO2Biomass Harvest
Atm
osph
eric
CO
2
Tools for characterizing effects of both climate change and land use change
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Miscanthus and Switchgrass
Davis , Parton et al. 2011 in press
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gC m-2 yr-1
< -450-450 to -300-300 to -150-150 to -75-75 to -50-50 to -25-25 to 2525 to 50> 50
ba
c d
Corn Miscanthus
Switchgrassno fertilizer
Switchgrassfertilizer
Net Greenhouse Gas Fluxes
Davis , Parton et al. 2011 in press
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gC m-2
< 20002000 - 22502250 - 25002500 - 27502750 - 30003000 - 35003500 - 40004000 - 45004500 - 5000> 5000
ba
c d
Corn Miscanthus
Switchgrassno fertilizer
Switchgrassfertilizer
Soil Carbon
Davis , Parton et al. 2011 in press
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Land Use Change
• A controversial issue for biofuels• Scaling beyond the case study is very difficult• Political forces are sometimes inhibitory • We need internationally standardized land use
monitoring and databases– See Davis et al. 2011 in Journal of the Royal Society Interface
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Eastern US Forest Carbon Sink
• Regenerating forests – Caspersen et al. 2000, Schimel et al.
2000, McGuire et al. 2001, Hurtt et al. 2002, Goodale et al. 2002, Houghton 2003, Nabuurs et al. 2003
• Climate change– Schimel 1995, Cao & Woodward 1998,
Kicklighter et al. 1999, Joos et al. 2001, Joos et al. 2002, McGuire et al. 2001
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Loblolly Pine Production
0 20 40 60 80 100 1200
200
400
600
800
1000
1200
1400
Modeled
Measured
Age (years)
Woo
d Pr
oduc
tion
(g m
-2 y
1)
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Pine Plantation Harvests
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How do forested respond to climate change over time?
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Loblolly pine production over time
Drake, Davis, Raetz, DeLucia 2010 Global Change Biology
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Photosynthetic Response to CO2
Ca
Ci
Ci :Ca is proportional to photosynthesis (A)
Lower Ci:Ca means more 13C is assimilated
= 12CO2 + 13CO2
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Do young and old forests respond similarly to climate change?
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Old forests have experienced the changing atmospheric CO2
concentration
Is the gradual response to CO2 over a century similar to the instantaneous response?
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Historical response vs. Projected Response
0 25 50 75 100 1250.4
0.5
0.6
0.7
0.8
f(x) = 0.671955237043418 exp( 0.00022664236946638 x )R² = 0.0749045292689528
f(x) = 0.638970017747953 exp( − 0.00197431821238338 x )R² = 0.723673849062812
Ca in current yearExponential (Ca in current year)Ca in establishment year
Forest Age (y)
Ci:C
a
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Physiological Constraints on Response to CO2 vary over time
0 25 50 75 100 1251.01.11.11.21.21.31.31.41.41.5 Ci:Ca in current year
Ci:Ca in establishment year
Forest Age (y)
delA
max
at 4
58 p
pm C
O2
380 580 780 980 1180 13807
12
17
22
27
Atmospheric CO2
Amax
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Summary
• Soil carbon sequestration is greater in perennial crops than row crops.
• There is a need for internationally standardized land use data.
• Older forests may be more responsive to increases in atmospheric CO2 than younger forests.
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Acknowledgements
• Steve Del Grosso• Evan DeLucia• John Drake• Cindy Keough• Ernest Marx• Tim Mies• Steve Long• Bill Parton• Lisa Raetz
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