COMPARISON OF 2 ENERGY FOREST GROWTH-MODELS BASED ON PHOTOSYNTHESIS AND NITROGEN PRODUCTIVITY

Two energy forest growth models are compared. The growth rate in the 1st model (N model) is determined by the amount of N in leaves and the N productivity. The growth rate in the 2nd model (photosynthetic model) is mainly determined by the photosynthetic process in the leaves, which in turn depends on climatic conditions and N status of the leaves, and on allocation. When 2 parameters related to those of the N model are derived from the photosynthetic model and the significances of these sets of parameters compared, some suggestions for changes to both models so as to make them consistent can be made. Allocation of biomass between stems, leaves and roots is a function of the N concentration in the leaves whereas the net fraction of growth lost through growth respiration in leaves and roots and death of fine roots in almost independent of the N concentration in leaves. The N model yields too large an influence for increasing leaf biomass on growth rate to be explained only by the effect of increasing self-shading in a growing canopy. In steady state conditions the photosynthetic model has no maximum leaf biomass when not considering death of biomass, while the N model leaf biomass is limited even without death of leaf biomass.