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