Stand growth model based on carbon uptake and allocation in individual trees

A stand growth model based on individual tree growth, with a time step of 1 year and a time span equivalent to the rotation period, is presented. The model applies to Scots pine (Pinus sylvestris) in the boreal zone. The individual tree model describes annual net photosynthetic production and its allocation to different growth compartments. The model differs from many related ones in that inter-tree competition is explicitly described through the physical environment. Instead of defining a competition index, the concept of photosynthetic light ratio is applied. This is the ratio between actual photosynthesis produced under shade from other trees and the potential, or unshaded photosynthesis. The model estimates mass flows of the system and describes the differentiation of individual trees during stand development. Canopy closure is defined as the attainment of maximum needle biomass, which is soon followed by a decline in the amount of needles. Stem volume growth declines in the later development of the stand. Biological assumptions underlying these phenomena are discussed. Behaviour of the model is demonstrated with the aid of simulations of a natural stand and a planted stand