Estimation of growth model in uneven – aged forests (Case study: Iranian Caspian forests)

The aim of this study was to estimate a diameter growth model for individual trees in uneven –aged Caspian forests. Three sample plots in the same aspect and of the same forest type were selected. In each sample plot, full callipering was conducted and the parameters such as total tree height, diameter at breast height, distance of neighbor trees and azimuth were measured. In each plot, 30 trees were selected and drilled with increment borer, in order to determine the growth model. Regression analysis was used to estimate the growth model. The analysis shows that, for individual trees, there is a strongly significant nonlinear relation between the annual basal area increment, as the dependent variable, and the basal area of the individual trees. The results also show, that the basal area of competing trees, in the sample, has a positive influence on growth. The estimated result that increment is higher with more competing neighbor trees is probably obtained because of the following reason: The plots with higher volume per hectare, and more “competition”, most likely also have higher “site index” or “better soil” or “better forest production conditions” than the plot with lower volume per hectare.