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Abstract
Introduction
Climatic conditions of Central Polissya region, in general, are favourable for Scots pine (Pinus sylvestris L.). However, pine stands decline has been progressing in the region since the beginning of this decade. Similar processes are recorded in other regions of Europe. They are often explained by climate change and considerable anthropogenic impact.
The increase of bark beetle foci area is connected with an increase of forest susceptibility and tolerance to damage, change in the microclimate of some plots due to anthropogenic influence, as well as an acceleration of insects’ seasonal development. At the same time, the spread of pine forest decline is not homogeneous even within the same region, which is connected both with relief, climate and soil diversity, as well as with different availability of preferable forest plots for colonization. In declining Scots pine stands of Central Polissya zone, engraver beetle Ips acuminatus (Gyllenhal, 1827) and six-toothed bark beetle Ips sexdentatus (Boerner, 1767) (Curculionidae, Scolytinae) are the most spread, due to their ability to develop in several generations per year depending on weather conditions.
The aim of the research was to evaluate the changes of climate factors in Central Polissya, which can contribute to Scots pine vulnerability to bark beetle attacks and increase of their population density.
Materials and Methods
Investigations included statistical and comparative analysis of climate indices, which were evaluated using long-term values of air temperature and precipitation from database https:/climate-data.org and respective values for 2005–2018 from http://rp5.ua. Six meteorological stations were chosen for analysis: Olevsk, Ovruch, Korosten, Teteriv, Novohrad-Volynskyi and Zhytomyr. Annual air temperature, growing season temperature, the sum of positive temperatures for growing season, growing season precipitation and G. T. Selyaninov hydrothermal index (HTI) were evaluated for long-term data and data for 2005–2018.
Results
In 2005–2018 an average annual and growing season air temperature increased, especially in the southern part of the region. On temperature conditions until 2009, multivoltine bark beetles were possible to develop only one full generation. Thermal conditions in Scots pine stands in the vicinity of five meteorological stations in 2010, three meteorological stations in 2012, two meteorological stations in 2015, one meteorological station in 2016, and five meteorological stations in 2018 were favourable for the development of two bark beetle generations.
Conclusions
We came to the conclusions that the average growing season precipitation for 2005–2018 was inferior to the long-term data for all analyzed meteorological stations, except Olevsk. The average G. T. Selyaninov hydrothermal index value fell to the Forest-Steppe “standard” in 2005 and 2009 and to the Steppe “standard” in 2015. Such decrease is unfavourable for forest trees, which are adapted to the high humidity of air and soil.
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