carbon dynamics: perspectives from ecosystem models sarah c. davis interface meeting, captiva island...
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Carbon dynamics: perspectives from ecosystem models
Sarah C. Davis
Interface Meeting, Captiva Island FlMarch 2, 2011
Major challenges• Long-term responses to climate change• Effects of land use change
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
Ecosystem modeling approach
• Comparative ecosystem physiology
• Comparative ecosystem biogeochemistry
• Coupled to hypothesis-driven research
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)
Example of biogeochemistry- driven model
Parton et al. 1998
Miscanthus x giganteus
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
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
Miscanthus and Switchgrass
Davis , Parton et al. 2011 in press
gC m-2 yr-1
< -450
-450 to -300
-300 to -150
-150 to -75
-75 to -50
-50 to -25
-25 to 25
25 to 50
> 50
ba
c d
Corn Miscanthus
Switchgrassno fertilizer
Switchgrassfertilizer
Net Greenhouse Gas Fluxes
Davis , Parton et al. 2011 in press
gC m-2
< 2000
2000 - 2250
2250 - 2500
2500 - 2750
2750 - 3000
3000 - 3500
3500 - 4000
4000 - 4500
4500 - 5000
> 5000
ba
c d
Corn Miscanthus
Switchgrassno fertilizer
Switchgrassfertilizer
Soil Carbon
Davis , Parton et al. 2011 in press
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
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
Loblolly Pine Production
0 20 40 60 80 100 1200
200
400
600
800
1000
1200
1400
Modeled
Measured
Age (years)
Wo
od
Pro
du
ctio
n (
g m
-2 y
1)
Pine Plantation Harvests
How do forested respond to climate change over time?
Loblolly pine production over time
Drake, Davis, Raetz, DeLucia 2010 Global Change Biology
Photosynthetic Response to CO2
Ca
Ci
Ci :Ca is proportional to photosynthesis (A)
Lower Ci:Ca means more 13C is assimilated
= 12CO2+ 13CO2
Do young and old forests respond similarly to climate change?
Old forests have experienced the changing atmospheric CO2
concentration
Is the gradual response to CO2 over a century similar to the instantaneous response?
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
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
Am
ax
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.
Acknowledgements
• Steve Del Grosso• Evan DeLucia• John Drake• Cindy Keough• Ernest Marx• Tim Mies• Steve Long• Bill Parton• Lisa Raetz