The aim of the research was to determine the rate of the damage of xylophagous insects for silver birch (Betula pendula Roth.) stands in the Left Bank Forest-steppe of Ukraine. Evaluation of physiological harmfulness considered a health condition of inhabited trees, features of maturating feeding and pathogens vectoring for the cases of so-called ‘provoked aggressiveness’ and its absence. Evaluation of technical harmfulness considered a location and depth of larval galleries and pupal chambers, colonized sapwood surface, and stem part. Evaluation of general harmfulness considered physiological harmfulness, technical harmfulness and generation number. Among 22 xylophagous insect species, 4 species were widespread (Agrilus viridis (Linnaeus, 1758), Xylotrechus rusticus (Linnaeus, 1758), Xyleborinus saxeseni (Ratzeburg, 1837), and Xyleborinus attenuatus (Blandford, 1894)); 3 species were common, 6 species were rare and 9 species were single. The highest physiological harmfulness is expected for Tremex fuscicornis (Fabricius, 1787) and Tremex magus (Fabricius, 1787), Сhrysobothris affinis (Fabricius, 1774), Agrilus viridis (Linnaeus, 1758), Xylotrechus rusticus, and bark beetles. The highest technical harmfulness is expected for wood wasps – Tremex spp., jewel beetles Dicerca furcata (Thunberg, 1787) and Dicerca alni (Fischer von Waldheim, 1824), longhorn beetle Xylotrechus rusticus, and xylomycetophages – Xyleborinus sp. All widespread species are evaluated by a wide range of physiological harmfulness. Three of them (all except Agrilus viridis) are evaluated by highly technical harmfulness and from moderate to highly general harmfulness. Among the species having a common occurrence, Tremex fuscicornis can be highly harmful only in the case of tree weakening by negative factors, another two species can be non-harmful, and Xiphydria longicollis (Geoffroy, 1785) can be low harmful in the case of tree weakening by negative factors. Among the rare species, Scolytus ratzeburgi Janson, 1856 can be low or moderately harmful and Tremex magus can be low or highly harmful depending on the presence or absence of other negative factors. Among single species, Zeuzera pyrina (Linnaeus, 1761) can be moderately harmful because it colonizes almost healthy trees. The rest three species can be moderately harmful in the case of tree weakening by negative factors.
Silver birch (Betula pendula Roth.) forms softwooded broadleaved forests in various natural zones. It is widely used in protective afforestation and urban plantings, it is a pioneer species in the clear-cuts and burnt areas. However, the global warming and anthropogenic pressure promote the susceptibility of silver birch to pests and pathogens. The aim of the research was to assess the trends in the health condition dynamics of silver birch stands depending on forest site conditions and the initial health condition of the trees. The research was carried out in the 2015-2019 period in the Silver birch forest stands in Kharkiv region in fresh fairly poor forest site conditions (B2), fresh fairly fertile forest site conditions (C2), and fresh fertile forest site conditions (D2). All the stands were 40–45 years old and had a relative density of stocking 0.7–0.8. Health condition class was visually assessed for each tree in July of each year according to “Sanitary rules in the forests of Ukraine”. For each group of sample plots, which corresponded to the main types of forest site conditions, the probability of improvement of health condition, deterioration of health condition, and mortality in 2019 was calculated depending on their health condition in 2015. In each year of the studies (2015–2019), the health condition of silver birch stands was the worst in fresh fertile site conditions, which was due to the bacterial wet wood disease. In the fresh fertile forest site conditions, no tree of the 4th class of health condition improved it during the 2015–2019 period, and in fresh fairly fertile forest site conditions 27.7% of silver birch trees improved their health condition. In each type of forest site conditions, the probability of mortality in more weakened silver birch specimens is higher. The probability of silver birch mortality of any class of health condition was the highest in the fresh fertile forest site conditions and the lowest in the fresh fairly poor forest site conditions.
Recently health condition of silver birch (Betula pendula Roth.) stands worsens in the forest and ornamental stands. It is important to know the probability of its improvement or deterioration in particular stands to take the necessary measures in time. The aim of the research was to assess the trends in the health condition dynamics of silver birch stands depending on their age class and the initial health condition of the trees. The research was carried out in 2015-2019 in the Silver birch linear stands in two parks of Kharkiv National Agrarian University named after V.V. Dokuchaev (49º53' N, 36º27' E). Five sample plots of the 3th age class are located in Veterans Park and the other 4 sample plots of the 5rd age class – in Arboretum of this University. For each inspected tree diameter at breast height (DBH) was measured in 2015 and 2019. Crown defoliation and health condition class were visually assessed in July of each year. Health condition index (HCI) was calculated as mean weighted from trees number of each category of health condition, separately for all living and dead trees (HCI1–6) and for living trees only (HCI1–4). Tree mortality was expressed as a percentage of lost (dead) trees for research period out of the total trees in 2015. It was shown that the silver birch stands of the 3rd age class didn't change their health condition for 2015-2019 or improved it. The stands of the 5th age class worsened their health condition in three sample plots and improved it in one sample plot. Within each age class, the stands of lower diameter class had a worse health condition. Tree mortality was registered in two out of five sample plots in the stands of the 3rd age class and in three out of four sample plots in the stands of the 5th age class. In the stands of the 5th age class the trees from the stands of the smallest diameter class characterized by the highest mortality level (22.4%) and the worse health condition (HCI1-4 =2.8). In pooled sample of plots, the death probability for silver birch trees, which 4 years ago had the 1st class of health condition is 3.5%, those of the 2nd class have the death probability of 10.7%, the trees of the 3rd class – 36.9%, those of the 4th class – 84.6%. As for an initially weakened stand, its trees which 4 years ago had the 1st, the 2nd, the 3rd or the 4th health condition class, have the death probability of 5%, 18.5%, 33.3%, and 100% respectively. Thus, the weakened silver birch stand which contains trees of 1st - 3rd classes of health condition is able to restore condition to a healthy one, and the deterioration may be expected only for severely weakened trees (having 3rd class of health condition in 2015). The weakened silver birch stand which has the trees of 1st - 4th health condition classes is most likely to weaken even more severely over 4 years.
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