Foliage profiles of individual trees determine competition, self-thinning, biomass and NPP of a Ctyptomeria japonica forest stand: A simulation study based on a stand-scale process-based forest model

A simulation study was carried out to investigate simultaneously the effects of eco-physiological parameters on competitive asymmetry, self-thinning, stand biomass and NPP in a temperate forest using an atmosphere-vegetation dynamics interactive model (MINoSGI). In this study, we selected three eco-physiological relevant parameters as foliage profiles (i.e. vertical distribution of leaf area density) of individual trees (distribution pattern is described by the parameter eta), biomass allocation pattern in individual tree growth (chi) and the maximum carboxylation velocity (V-max) The position of the maximal leaf area density shifts upward in the canopy with increasing eta. For scenarios with eta 4 (foliage concentrated in the lowest canopy layer) or eta > 12 (foliage concentrated in the uppermost canopy layer), a low degree of competitive asymmetry was produced. These scenarios resulted in the survival of subordinate trees due to a brighter lower canopy environment when eta 4 or the generation of spatially separated foliage profiles between dominant and subordinate trees when eta > 12. In contrast, competition between trees was most asymmetric when 4 <= eta <= 12 (vertically widespread foliage profile in the canopy), especially when eta = 8. In such cases, vertically widespread foliage of dominant trees lowered the opportunity of light acquisition for subordinate trees and reduced their carbon gain. The resulting reduction in carbon gain of subordinate trees yielded a higher degree of competitive asymmetry and ultimately higher mortality of subordinate trees. It was also shown that 4 <= eta <= 12 generated higher self-thinning speed, smaller accumulated NPP, litter-fall and potential stand biomass as compared with the scenarios with eta 4 or eta > 12. In contrast, our simulation revealed small effects of chi or V-max on the above-mentioned variables as compared with those of eta. In particular, it is notable that greater V-max would not produce greater potential stand biomass and accumulated NPP although it has been thought that physiological parameters relevant to photosynthesis such as V-max influence dynamic changes in forest stand biomass and NPP (e.g. the greater the V-max, the greater the NPP). Overall, it is suggested that foliage profiles rather than biomass allocation or maximum carboxylation velocity greatly govern forest dynamics, stand biomass, NPP and litter-fall. (C) 2009 Elsevier B.V. All rights reserved.