Modeling Forest EcosystemEnergy, Carbon and WaterFluxes: Impacts of CanopyStructureModeling Forest EcosystemEnergy, Carbon and WaterFluxes: Impacts of CanopyStructure
Conghe SongConghe Song
Department of GeographyDepartment of Geography
University of North CarolinaUniversity of North Carolina
Chapel Hill, NC 27599Chapel Hill, NC 27599
Small Leaves do the Big JobSmall Leaves do the Big Job
CO2
H2O
Losing water is the price to pay for gaining CO2
stoma
Underside
Big-Leaf Scaling upBig-Leaf Scaling up
Sunlit and Shaded leavesSunlit and Shaded leaves
photosynthesis
Light intensity
Sunlit leaves
Shaded leaves
I1
I2
I3
Two-Leaf Scaling upTwo-Leaf Scaling up
Sunlit leaf
Shaded leaf
Uniform vs Gappy CanopyUniform vs Gappy Canopy
Uniform Canopy
Gappy Canopy
Sun flecks
Gap Effects on Light AbsorptionGap Effects on Light Absorption
Research Question
What are the impacts of canopy structureon energy balance, carbon assimilationand 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 VerificationSources 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:
4.7-5.9
Tow-layer Canopy for the Loblolly Pine at DFTow-layer Canopy for the Loblolly Pine at DF
Each layer is independent of the other layer so thatthe gaps are calculated separately and then anoverall gap probability is derived for the entirecanopy.
broadleaf
layer
Conifer
layer
Model InputsModel Inputs
Incoming radiationIncoming radiation
PrecipPrecip
Air tempAir temp
Soil tempSoil temp
Soil moistSoil moist
Wind speedWind speed
VPDVPD
LAILAI
All input data are obtained from the on-site measurements.
Net Radiation
Q
Qr
La
Ls
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 RadiationVerification of Net Radiation
Latent Heat (Evapotranspiration)Latent Heat (Evapotranspiration)
Transpiration
Evaporation
Uniform Canopy vs. Gappy Canopy (two-leaf scaling up)
+
= Evapotranspiration
H2O
H2O
Verification of Latent Heat
Carbon Assimilation
Plant
Transpiration
Net
PSN
Verification of Net Carbon Assimilation
ConclusionsConclusions
Canopy structure has significant impacts on energyinterception, carbon assimilation, and transpiration.
A gappy canopy allows more radiation passing through thecanopy to reach the forest floor and helps plants trap moreheat.
A uniform canopy can lead to overestimate of carbonassimilation and transpiration by plants.