SPREAD OF SCOTS PINE STANDS DECLINE IN KOROSTYSHIV FOREST ENTERPRISE 1

The aim of the research was to reveal the features of Scots pine stands decline in Zhytomyr (Central) Polissya using the case of Korostyshiv Forest Enterprise. The investigations included statistical and comparative analysis of the database of forest fund of the State Association “Ukrderzhlisproekt”, the data of forest pathological survey of pine stands in Korostyshiv Forest Enterprise and reports on sanitary felling in 2014–2017. Bark beetles (72.4–95.8 %), fungal diseases (0.4–9.1 %) and weather conditions (3.5–27.5 %) were the main causes of Scots pine decline. A high proportion of pure Scots pine stands and the stands over 50 years old are the main predisposing factors of forest decline. Abnormal increase in air temperature and a decrease in Selyaninov’s Hydro-thermal Coefficient to the level of Steppe zone were inciting factors of forest decline, and bark beetles were a contributing factor to it. K e y w o r d s : Scots pine (Pinus sylvestris L.), forest decline, Selyaninov’s Hydro-thermal Coefficient, forest composition, age structure, relative density of stocking.

Investigation of stem insects foci development and spread show its diversity in different regions and stands, owing to climatic features and tree reaction on it (Meshkova and Borysenko 2017).
The aim of our research was to reveal the features of Scots pine decline in Zhytomyr (Central) Polissya on the example of Korostyshiv Forest Enterprise.
Materials and Methods.The investigations included statistical and comparative analysis of forest fund database of the State Association "Ukrderzhlisproekt", the data of forest pathological survey of pine stands in Korostyshiv Forest Enterprise and reports on sanitary felling in 2014-2017.
Monthly air temperature and precipitation datasets were taken from Zhytomyr meteorological station (50° 15' N 28° 39' E).Selyaninov's Hydro-thermal Coefficient -HTC (Selyaninov, 1937) was calculated by the formula: where ΣP is precipitation for the period with mean month air temperature over 10°C, mm; Σt is the sum of daily air temperatures for the same period, °C.Statistical analysis was carried out with the help of MS Excel.A tetrachoric correlation was evaluated to compare pine stands distribution by stand composition, age and stocking density in the foci of bark beetles and in other pine stands, and the reliability was assessed by χ 2 criterion (Atramentova & Utevskaya 2008).
Results and Discussion.The area of selective sanitary felling in Korostyshiv Forest Enterprise tended to decrease, and the area of clear sanitary felling tended to increase until 2016 and then to decrease (Fig. 1).The proportion of selective felling was close to 100 % in 2014, decreased to 82.4 % in 2016 and increased to 95.5 % in 2017.Weather conditions, bark beetles and fungal diseases were the main causes of Scots pine decline (Fig. 2).Area of Scots pine stands decline, as a result of fungal diseases, was the lowest.The average annual area of such decline was 61.7 ha, and it varied from 11.3 to 120.6 ha in different years.The proportion of forest decline from fungal diseases varied from 0.4 % in 2014 to 9.1 % in 2017.Root rot Heterobasidion annosum (Fr.)Bref was the main cause of sanitary felling from all fungal diseases.However, ophiostomatoid fungi associated with bark beetles were rather widely represented in bark beetles foci and took an important part in Scots pine decline.

Bark beetles Total
Weather conditions were considered as the cause of Scots pine decline in 384.5 ha on average.The area of forest decline from this reason was the highest in 2014 (738.6 ha) and drastically reduced (over 10 times) in 2016.The proportion of forest decline as a result of adverse weather conditions was 27.5 and 26.5 % from the total decline in 2014 and 2015, and only 3.5 and 4.2 % in 2016 and 2017 respectively.
The area of forest decline as a result of bark beetles infestation was 1,708.4ha in average for four years.A slight tendency to decrease in this area is registered.However, the proportion of forest decline in result of bark beetles infestation increased from 72.4 % in 2014 to 95.8 % in 2016 and slightly decreased to 86.7 % in 2017 (see Fig. 2).
Analysis of weather conditions for 2005-2017 shows that annual air temperature exceeded the average long-term air temperature in 2007-2008 and 2013-2017 (Fig. 3).Abnormal increase in the air temperature was favorable for the development of additional generations of bark beetles (Meshkova et al. 2017).At the same time mutual effect of air temperature and precipitation in particular years influenced the Selyaninov's Hydro-thermal Coefficient, which was 1.2 in average for 2004-2017 that is lower than the range for Polissya zone (1.3-1.6)(Selyaninov 1937).This coefficient fell to 0.91 in 2009, continuously decreased in 2013-2015 to 0.65 and stayed rather low in 2016 and 2017 (0.8 and 0.82 respectively) (Fig. 4).Only three years from analyzed period Hydro-thermal Coefficient calculated by the dataset of Zhytomyr meteorological station was indicative for Polissya zone (1.33 in 2014, 1.55 in 2006, and 1.63 in 2007 and 2013).
Such decrease in HTC in Polissya is very unfavorable for forest trees, which are adapted to the high humidity of air and soil.
Analysis shows (Fig. 6) that the proportion of Scots pine stands older than 50 years old among declining stands is considerably less than among all stands (χ 2 fact.=1049.0;χ 2 0.05 =3.8).In all Scots pine stands and in declining Scots pine stands the area with the relative density of stocking 0.7 is the highest (48.4 and 60.5 % respectively) (Fig. 7).

Fig. 1 -
Fig. 1 -Dynamics of clear sanitary felling and selective sanitary felling area in Korostyshiv Forest Enterprise in 2014-2017

Fig. 2 -
Fig. 2 -Dynamics of Scots pine stands area decline from different causes in Korostyshiv Forest Enterprise in 2014-2017

Fig. 5 -
Fig. 5 -Area distribution for stands with different Scots pine participation among all Scots pine stands and declining Scots pine stands (Korostyshiv Forest Enterprise, 2014-2017)

Fig. 6 -
Fig. 6 -Area distribution for all Scots pine stands older than 50 years old and declining Scots pine stands older than 50 years old (Korostyshiv Forest Enterprise, 2014-2017)

Fig. 7 -
Fig. 7 -Area distribution for stands of different relative density of stocking among all Scots pine stands and declining Scots pine stands (Korostyshiv Forest Enterprise, 2014-2017)