Scaling leaf photosynthesis to canopy in a mixed deciduous forest. II. A simulation study for two growing seasons

Abstract

The model as described in Samson et al. (1997) (FORUG model) is validated at the leaf level, and seems to simulate well the canopy rates for the different species and the different considered layers in the canopy. The highest instantaneous canopy photosynthesis rates are found for oak, the lowest for beech. The total amount of carbon assimilated during the growing season was highest for oak and ash and lower for beech and amounted respectively 10.9, 11.0 and 10.3 ton C ha-1 y-1 for the growing season 1996. The carbon uptake was higher during the growing season 1997 due to a higher mean daily temperature, and a higher amount of incoming PAR. For bole respiration the maximum rate for both growing seasons amounted 3.6 µmol m-2 S-1. Integrated over the growing season the total bole respiration amounted 4.5 and 4.3 ton C ha-1 y-1 for respectively the growing season 1997 and 1996. At high temperatures and high PPFD, temperature becomes a limiting factor for Net Canopy Photosynthesis (NCP). A total forest canopy has, just as leaves, a curvilinear reaction on PPFD. This finding allowed to construct a one-layer or 'big leaf' model which simulated-the NCP as well as did the multi-layer FORUG model. However a multi-layer model for simulating the NCP is preffered as it allows more simpler incorporation or adaptation of parameters.