It is documented that severity and frequency of foliage browsing insects’ outbreaks in the Steppe zone of Ukraine exceed such parameters in Forest Steppe zone. Among other foliage browsing insects, European pine sawfly (Neodiprion sertifer Geoffr.) is the most spread. Its outbreaks usually develop in a cyclic manner with an interval of 9–12 years.
Over 40 % of European pine sawfly foci are located in Kherson administrative region. The main part of this region belongs to Low Dnieper region, where the forest was planted on moving sands over 60 years ago. There, the forest is mainly represented by pure pine plantations, which grow on the southern timberline. European pine sawfly was found in these stands for the first time in 1965, and now its foci of mass propagation sometimes exceed 40,000 ha, and outbreaks continue almost constantly.
For planning the strategy of forest protection, the analysis of modern foci area dynamics of European pine sawfly is necessary in artificial stands of Low Dnieper region considering foci area distribution by the threat of crown damage.
The aim of the research was to estimate the parameters of European pine sawfly outbreak in the Low Dnieper region for 2010–2017.
Materials and Methods
Statistical data on the area of European pine sawfly foci from six State Forest Enterprises of Kherson and Mykolaiv Administrations of Forest & Hunting management as well as from the State Specialized Forest Protection Enterprise “Khersonlisozakhyst” for 2010–2017 were used in the analysis. The area of pine stands in these State Forest Enterprises was recognized from the database of Production Association “Ukrderzhlisproekt”.
To characterize outbreak of European pine sawfly, we evaluated outbreak incidence, severity, the interval between outbreaks and duration for different forest enterprises. Outbreak severity was calculated as foci area (thousand hectares) and specific foci area as the ratio of foci area (hectares) and pine stands area (thousand hectares). Outbreak frequency or probability was evaluated as the part of outbreak years from the duration of the analyzed period.
Mean score of stand threat from European pine sawfly damage was suggested to calculate considering foci area distribution by the threat of crown damage.
Results and Conclusions
The area of European pine sawfly foci with the threat of forest damage over 25 % was from 499.3 ha in the SE “Ochakivske Forest & Hunting Enterprise” and 991.0 ha in the SE “Kakhovske Forest Enterprise” up to almost 5,000 ha in the SE “Tsurupinske Forest & Hunting Enterprise”. For eight years one can distinguish only one European pine sawfly outbreak with a maximum in 2012 in the forest fund of all analyzed forest enterprises, except SE “Velykokopanivske Forest & Hunting Enterprise” with a maximum in 2013. Duration of the period with the threat of forest damage over 50 % during European pine sawfly outbreak did not exceed three years. Evaluation of the mean score of stand threat from European pine sawfly damage was suggested, which gives the possibility to compare the outbreak dynamics in the forest fund of different forest enterprises not taking into account the absolute values of foci area. The reasons for possible increase of the outbreak duration in the region are considered.
4 Figs., 2 Tables, 15 Refs.