A model for individual tree development based on physiological processes

A tree growth model is presented which calculates the 3D development of trees and stands in dependence on their individual carbon, water and nitrogen balance. The availability of energy, soil water and nutrients is estimated from field data at the scale of crown and root system fractions, taking into account the individual neighbourhood. The model includes a simple estimation of radiation distribution and the simulation of carbon and nutrient exchange. Senescence is represented by compartment-specific turnover rates. Allocation of carbon and nitrogen into foliage, fine roots, branches, coarse roots, and the stem is calculated according to functional balance and pipe model principles. Dimensional changes are calculated annually according to the distribution of net assimilation. The model describes tree development as a response to individual environmental conditions and changes environmental conditions with individual tree development. Due to this feedback loop, environmental influences can be assessed in any kind of species mixture or stand structure. Furthermore, the physiological-based approach ensures that the model can be used for investigations of complex environmental changes, e.g. CO2 concentration, precipitation, temperature and nitrogen deposition. Thus, it is particularly suitable to analyse field investigations and to support the cognition process on the ecology of forests. it could also be used, however, to estimate forest responses to given environmental scenarios.