Health condition of silver birch (<i>Betula pendula</i> Roth) in different forest site conditions of the Left-bank Forest Steppe of Ukraine
The goal of research was to reveal the peculiarities of two-year dynamics of health condition indices for silver birch ( Betula pendula Roth) in different types of forest site conditions of the Left-bank Forest Steppe of Ukraine. Presented data on silver birch health condition were obtained from 9 permanent sample plots in 2015- 2016. Three plots were located in a fresh subor (fresh relatively poor forest site conditions В2), other three plots in a fresh sugrud (fresh relatively fertile forest site conditions C2), and three more plots in a fresh grud (fresh fertile forest site conditions D2) (by Alekseyev-Pogrebnyak classification). These forest site conditions are the most represented in the region. All studied stands were of artificial seed origin and are about the same age (40-45 years old), which reflects the largest representation in the forests of the Left-bank Forest Steppe of Ukraine. Categories of health condition were assessed for each birch tree in the sample plots according to the «Sanitary rules in the forests of Ukraine». Index of forest health condition was evaluated by a number of trees and by the part of cross-sectional area of birch stems in each category of health condition. Index of forest health condition was calculated separately for all trees ( I I-VI) and for viable trees of the I-IV categories of health condition ( I I-IV). All evaluated indices of health condition (1.7-2.5) allow to suggest these birch stands weakened. There is a trend of worsening birch condition in 2016 comparing to 2015 as well as in the series «fresh relatively poor forest site conditions ( В 2) - fresh relatively fertile forest site conditions ( С 2) - fresh fertile forest site conditions ( D 2)». Worsening of health condition was registered mainly in trees with smaller diameter, thus pathological processes were not extensive in the stands as whole. Dieback, epicornic shoots, stem insects' entrance holes and galleries, and sap flux on stems were registered as the signs of stands weakening. In 2016 in comparison to 2015, the performance of wetwood has increased.