1. Modeling Forest Ecosystem Energy, Carbon and Water Fluxes: Impacts of Canopy Structure
Conghe Song
Department of Geography
University of North Carolina
Chapel Hill, NC 27599

2. Small Leaves do the Big Job
Underside
CO2
H2O
stoma
Losing water is the price to pay for gaining CO2

3. Big-Leaf Scaling up

4. Sunlit and Shaded leaves
photosynthesis
Sunlit leaves I1 I2 I3
Light intensity

5. Two-Leaf Scaling up
Sunlit leaf
Shaded leaf

6. Uniform vs Gappy Canopy
Uniform Canopy
Gappy Canopy
Sun flecks

7. Gap Effects on Light Absorption

8. Research Question
What are the impacts of canopy structure on energy balance, carbon assimilation and transpiration?

9. Impacts of Canopy Structure on Ecosystem Processes
Uniform Canopy
Gappy Canopy
Photosynthesis
Eco-physiological
Intercepted Radiation
(two leaf scaling up)
models
Transpiration

10. Sources of Data for Model Verification
Pine density:
1377~1299 trees/ha
Understory hardwoods:
1470~1389 trees/ha
Leaf area index:
AmeriFlux
Tower
Duke Forest FACE Site
Measured Data: net radiation, evapotranspiration, net ecosystem exchange
during May to Sept for 2001, 2002, 2003

11. Tow-layer Canopy for the Loblolly Pine at DF
Conifer
layer
broadleaf
layer
Each layer is independent of the other layer so that the gaps are calculated separately and then an overall gap probability is derived for the entire canopy.

12. Model Inputs Incoming radiation Precip Air temp Soil temp Soil moist
Wind speed
VPD
LAI
All input data are obtained from the on-site measurements.

13. Net Radiation La Q Radiation Budget: Qr Ls
Energy Budget: Net radiation is used for heat storage in the soil and plant body, evaporate water (latent heat), heating the air near the surface (sensible heat), and photosynthesis

14. Verification of Net Radiation

15. Latent Heat (Evapotranspiration)+
Evaporation
= Evapotranspiration
H2O
H2O
T=f(Rnet, gs, ga, VPD, T)
Uniform Canopy vs. Gappy Canopy (two-leaf scaling up)

16. Verification of Latent Heat

17. Carbon Assimilation Soil Net Plant Resp. PSN Resp.
Tower Measurement: Net Ecosystem Exchange (NEE)
Measured data cannot separate Net PSN from plant (stems, leaves and roots) and soil (dead biomass) respiration. A model is needed to estimate the plant and soil respiration in order to get Net PSN.

18. Verification of Net Carbon Assimilation

19. Conclusions
Canopy structure has significant impacts on energy interception, carbon assimilation, and transpiration.
A gappy canopy allows more radiation passing through the canopy to reach the forest floor and helps plants trap more heat.
A uniform canopy can lead to overestimate of carbon assimilation and transpiration by plants.