Canadian Forest Service Publications
A model of canopy-level photosynthesis and its application in gap filling of flux data. 2006. Xing, Z.; Bourque, C.P-A.; Meng, F.-R.; Cox, R.M.; Swift, D.E. Pages 184-188 in Chinese National Committee for the International Geosphere-Biosphere Programme, compiler. Proceedings, International Conference on Regional Carbon Budgets, August 16-18, 2006, Beijing, China. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre, Fredericton, N.B.
Available from: Atlantic Forestry Centre
Catalog ID: 26910
Data gaps in flux data has been a serious problem for many years. Although many different methods have been developed for gap filling of eddy covariance measurements, including net ecosystem productivity (NEP) measurements, there lacks a standard, commonly acceptable solution for gap filling. This paper describes a simple, but ecologically based method for gap filling of NEP measurements. The model couples processes of photosynthesis and stomatal conductance through the dynamic calculation of the internal carbon dioxide (CO2) concentration in leaves. The model contains three response functions, one for temperature, CO2 concentration, and light intensity. To account for light variation in the canopy, the canopy is divided into four layers of equal depth with each layer being assigned a proportion of the total canopy LAI, i.e., LAI resident volume in a layer to the total crown volume, assuming conical crowns. The canopy layers are subdivided into portions of shaded and sunlit leaves to capture the daily variation in incident solar radiation and photosynthesis. Because of the model’s simplicity and low input data requirement, model parameters are readily optimized with either the Simplex or Levenberg-Marquardt’s numerical convergence rules for periods when data exist. Comparison of model results to field measurements provide reasonable agreement, yielding r2 = 0.77.