Functions to determine site index of the principal forest species

We developed functions that describe the relationship between the stand top height and age for Scots pine (Pinus sylvestris), Norway spruce (Picea abies), silver fir (Abies alba), European larch (Larix decidua), English oak (Quercus robur), European beech (Fagus sylvatica), black alder (Alnus glutinosa) and silver birch (Betula pendula). We applied model proposed by Cieszewski for that purpose. The top height at the age of 100 years obtained from the developed models is a stand site index. Prior to the determination of function coefficients we analysed the height growth rate for each species to provide similar course of the height growth curves for the majority of trees. It required the elimination of trees whose height growth rate differed from the course parallel to the age axis. These were usually trees that remained under canopy for too long and reacted with an intensive increase in height growth after removal of the canopy, trees after insect gradation or trees growing in areas drained during their growth. The site index functions are the first stage of yield tables development. It is planned to introduce them into stand growth models, which will increase the accuracy of forecasting the development of wood resources.