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Abstract
Introduction
The part of Silver birch (Betulа рendulа Roth.) stands is about 7 % in the forest covered area of Ukraine and about 2 % in the Left-bank Forest-Steppe. Birch stands play an important ecological role and are also a source of forest resources. The decline of birch stands in Ukraine was registered in 1994. Stem insects and bacterial wetwood were the main causes of birch decline. It is known that infected trees can recover or die after 2–6 years depending on the initial tree health and environmental conditions.
Radial increment dynamics is the comprehensive indicator of forest condition and can be used for early diagnostics of forest decline.
The aim of the research was to reveal the peculiarities of Silver birch radial increment in the trees affected by wetwood disease in the Kharkiv green belt on the background of weather parameters.
Materials and Methods
The research was carried out in the permanent sample plot in the Pivdenne forestry of the State Enterprise “Kharkiv Forest Research Station” of the Ukrainian Research Institute of Forestry and Forest melioration named after G. M. Vysotsky in the 45-year-old pure birch stand. Mean diameter of stand was 19.5 cm, mean height was 22.5 m.
Wood cores were taken on November 8, 2016, on the breast height from 15 healthy trees and 15 trees affected by wetwood disease. The cores were air-dried, a little grinded, treated with chalk and wetted. The radial increment was measured using digital device HENSON.
Long-term radial increment dynamics (1999–2016) of wetwood affected and healthy Silver birch trees have been studied along with weather parameters (annual air temperature and precipitation, temperature and precipitation for April – August as well as for winter months). Respective correlation coefficients have been calculated, and the graphs of radial increment and weather parameters have been compared.
Results and Conclusions
It was revealed by dendrochronological methods that radial increment of wetwood affected birch trees in 2009–2016 was 22 % less than such of healthy trees. Annual air temperature for this period 0.7°С (or 8 %) exceeded long-term data. In connection with 46.6 % exceeding of April – August precipitation in 2016, the radial increment of 88 % wetwood affected birch trees has increased. Correlation coefficients between the radial increment of wetwood affected trees and meteorological parameters were significant more often than those of healthy trees. The radial increment of wetwood affected trees was limited by annual and winter precipitations as well as winter temperature. The radial increment of healthy trees is positively influenced by precipitation in September and air temperature in March, and it is negatively influenced by precipitation in December and air temperature in April.
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