Download Powerpoint

Carbon dynamics: perspectives
from ecosystem models
Sarah C. Davis
Interface Meeting, Captiva Island Fl
March 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
Example of a physiology-driven model
(PnET)
GPP
Maximum
gross
photosynthesis
Realized
gross
photosynthesis
Net photosynthesis
VPD
Radiation
Leaf nitrogen content
NPP
Basal
respiration
PAR
daylength
Day temperature
Night temperature
Realized
respiration
Example of
biogeochemistrydriven model
Miscanthus x giganteus
Parton et al. 1998
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 Models
productivity
Ecosystem
CO2
Atmospheric
Tools for characterizing effects of both climate
change and land use change
Ecosystem
productivity
Biomass
Atmospheric
Harvest
CO2
Miscanthus and Switchgrass
Davis , Parton et al. 2011 in press
Net Greenhouse Gas Fluxes
Corna
-2
gC m yr
-1
Switchgrass
c
no fertilizer
b
Miscanthus
Switchgrass
fertilizer d
< -450
-450 to -300
-300 to -150
-150 to -75
-75 to -50
-50 to -25
-25 to 25
25 to 50
> 50
Davis ,
Parton et al.
2011 in press
Soil Carbon
Corn
a
gC m-2
< 2000
Switchgrass
no fertilizer
c
Miscanthus
b
Switchgrass
fertilizerd
2000 - 2250
2250 - 2500
2500 - 2750
2750 - 3000
3000 - 3500
3500 - 4000
4000 - 4500
4500 - 5000
> 5000
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
Wood Production (g m-2 y1)
1800
1600
Modeled
1400
Measured
1200
1000
800
600
400
200
0
0
20
40
60
Age (years)
80
100
120
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
= 12CO2 + 13CO2
Ci
Ci :Ca is proportional to photosynthesis (A)
Lower Ci:Ca means more 13C is assimilated
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
0.8
y = 0.672e0.0002x
R² = 0.0749
Ci:Ca
0.7
0.6
y = 0.639e-0.002x
R² = 0.7237
0.5
Ca in current year
Ca in establishment year
0.4
0
25
50
75
Forest Age (y)
100
125
Physiological Constraints
on Response to CO2 vary over time
Linear (Young)
1.5
1.4
1.4
1.3
1.3
1.2
1.2
1.1
1.1
1.0
delAmax at 458 ppm CO2
Ci:Ca in current year
Ci:Ca in establishment…
Linear (Old)
27
Amax
22
17
12
7
0
25
50
75
Forest Age (y)
100
125
380
580
780
980
1180
Atmospheric CO2
1380
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