Prognoza rozwoju drzewostanów lasu naturalnego z wykorzystaniem modelu według klas wymiarów

The size−class growth model is an empirical model applicable for the prediction of the dynamics of natural forest growth. It is based on the following assumptions: (1) changes in the forest condition are determined on the basis of the sum of the changes that take place in individual size classes, (2) the trees in a given class are represented by single average tree, (3) the calculation of the future tree density distribution in size classes (fig. 1) is the main element of the prediction, and (4) the future tree density distribution is estimated on the basis of the initial structure, actual growth and mortality of trees in individual size classes. The aim of the research was to develop a size−class growth model to be used for the preparation of a medium−term forecast of natural forest dynamics. The study site is located on the Bukowa Góra Mt in the Roztoczański National Park (SE Poland). For the analyses we took all uneven−aged stands (128 ha in total) composed mostly of silver fir and European beech. The material was collected on 65 permanent sample plots every five years in the period 1991−2011. Trees with the breast height diameter (DBH)8 cm were measured on each sample plot (500 m), while smaller trees – on three smaller concentric plots. We calculated, separately for fir and beech, the relationship between the mortality of trees and their diameter (fig. 2), the relationship between the diameter increment of trees and their DBH (figs. 3−4), the rate of saplings (emh/em=0.3−1.3 m) growth into the first DBH class (DBH=0.1−1.9 cm). On the basis of these data, we elaborated a size−class growth model that we used to predict the development of timber resources (trees with DBH8 cm) at 10−year intervals in the period 2001−2041. In 2011, the predicted average standing volume was lower than the one actually measured. The forecast indicated an increase in the average standing volume (fig. 5), a reduction in the volume of ingrowth (fig. 6), an increase in the proportion of beech in the standing volume and ingrowth (figs. 5 and 7) and the maintenance of a similar density structure (fig. 8) throughout the period 2001−2041. The low accuracy of the prediction after 10 years (in 2011) was caused by the difference between the predicted and actual values of tree growth and mortality in the period 2001−2011.
Sylwan 160 (3): 207-218