REGRESION MODELS FOR ASSESMENT OF THE VOLUME INCREMENT OF THE FIR, BEECH AND SPRUCE IN FORESTS OF BEECH, FIR AND SPRUCE ON LIMESTONE IN FEDERATION OF BOSNIA AND HERZEGOVINA

UDK: 630*56(497.6) The paper displays research results of volume increment size of main tree species, fir, beech and spruce within mixed forests of beech, fir and spruce on limestone and dolomites in Federation of Bosnia and Hercegovina (FBiH). Fir and beech forests along with the spruce represent the most important part of forest resources in BiH. As LOJO (2013) points out, around 371 000 ha of these forests are located on limestone and dolomites and are selection forests for the most part. Knowledge of laws of changes in size of volume increment of selection stand of trees is necessary for high quality planning of forestry production. The paper explores changes of volume increment sizes especially for following tree species: fir, spruce and beech within mixed stand of trees. Research sample are measured sample plots from 799 mixed stand of trees larger than 40 ha recorded during 11 years' time during the creation of forest management plans. Stands of trees in which control recordings were conducted for the purpose of reliability of data were taken as a sample. Multiple regression models for estimation of volume increment size of fir, spruce and beech including two models for each species of trees. Models used for volume increment size estimation of mixed forest in optimal - normal state and models used for determination of volume increment that is as accurate as possible when the size of multiple independent factors that affect change in volume increment size are known. This paper explores dependence of change of volume increment on: site class expressed through average height of trees whose diameter is 50 cm, share of species of trees in the stand volume, degree of coverage of the ground with crowns of trees of medium diameter in stand of trees which was calculated based on the basal area of species of trees and share of deciduous trees in the stand of trees volume. For more precise model size of basal area of species of trees in stand of trees and average altitude were used.