Вариативность диаметров деревьев в древостоях липы мелколистной

Information on the distribution of trees by thickness grades in stands is necessary for planning selective fellings and the formation of environmentally sustainable and economically valuable plantations. The aim of this article is to characterize and compare the structural diversity of tree diameter distribution in mixed one- and two-age stands of Tilia cordata Mill. growing in the Arkhangelsk forestry of the Republic of Bashkortostan. Based on the data from 25 temporary sample plots, cluster analysis and visualization method based on empirical data of tree diameter distributions have identified 4 unimodal structural types of distributions and a descending (reverse J-shaped) one. Among the studied two-aged stands, distribution of stands by diameter at breast height with 2 peaks (bimodality) is not observed. It has been found that the coefficients of diameter variation steadily decrease with the age of the tree stand (Pearson correlation coefficient r = – 0.57 at p = 0.003) and an increase in the proportion of linden in the forest stand (r = – 0.71 at p < 0.001), and the distribution series are characterized by right-sided asymmetry. Tree size diversity has been assessed based on cross-sectional area data using the Shannon, Simpson, Gini and Siipilehto indices. A comparison of the Shannon and Simpson indices has shown that the structural diversity of tree diameter has been more complex in two-aged forests compared to one-aged ones. Both indices have provided a clear division of the studied two-aged stands into 2 unimodal types of diameter distribution. The Gini index (0.28–0.52) has indicated a high level of structural diversity and has reached high values (0.48–0.52) when the diameter distribution has been close to downward sloping. Large values of the Siipilehto index (0.63–1.05) have confirmed the unimodality of the diameter distributions of the stands, including for the peak-shaped type. It has been concluded that cluster analysis and the use of indices of dimensional diversity of diameters allow a better understanding of the structure of linden forests, and the indices for linden stands should become part of their further forestry assessments.