Modeling canopy CO₂ and H₂O exchange of a temperate mixed forest

We tested a multilayered model that simulated half-hour canopy CO ₂ and H₂O exchange of a temperate forest mixed with broadleaved trees and Korean pine. The variables input to the model for scaling the fluxes from leaf to canopy included the vertical profiles of height, canopy thickness, and leaf biomass of the five dominant tree species. The diurnal and seasonal patterns of modeled CO₂ and H₂O fluxes agreed with measured values well during the nonstressed periods, while the model showed overestimation during the water-stressed and high-temperature periods, which appeared infrequently in our study site. We showed a strong correlation between 20-layer daily modeled fluxes and eddy covariance measurements for CO ₂ (r² = 0.734) and H₂O (r² = 0.785), during May to September 2003-2007. Different layered methods exerted influence on the radiation absorption within the canopy sublayers and hence on the CO ₂ and H₂O flux outputs. CO₂ and H₂O fluxes based on the Gaussian 5-layered method were 8% and 1% lower than those based on the 20-layered method.