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

Small Leaves do the Big Job CO 2 H2OH2O Losing water is the price to pay for gaining CO 2 stoma Underside

Big-Leaf Scaling up

Sunlit and Shaded leaves photosynthesis Light intensity Sunlit leaves Shaded leaves I1I1 I2I2 I3I3

Two-Leaf Scaling up Sunlit leaf Shaded leaf

Uniform vs Gappy Canopy Uniform Canopy Gappy Canopy Sun flecks

Gap Effects on Light Absorption

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

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

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

Tow-layer Canopy for the Loblolly Pine at DF 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. broadleaf layer Conifer layer

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

Net Radiation Q QrQr LaLa LsLs Radiation Budget: 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

Verification of Net Radiation

Latent Heat (Evapotranspiration) TranspirationEvaporation Uniform Canopy vs. Gappy Canopy (two-leaf scaling up) + = Evapotranspiration H2OH2O H2OH2O

Verification of Latent Heat

Carbon Assimilation Plant Transpiration Net PSN

Verification of Net Carbon Assimilation

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.