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 Underside CO2 H2O stoma Losing water is the price to pay for gaining CO2

Big-Leaf Scaling up

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

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?

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

Sources of Data for Model Verification Pine density: 1377~1299 trees/ha Understory hardwoods: 1470~1389 trees/ha Leaf area index: 4.7-5.9 AmeriFlux Tower Duke Forest FACE Site Measured Data: net radiation, evapotranspiration, net ecosystem exchange during May to Sept for 2001, 2002, 2003

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.

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.

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

Verification of Net Radiation

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

Verification of Latent Heat

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.

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.