Сибирский лесной журнал (Feb 2023)
History of the Siberian moth outbreaks at the eastern foothills of Kuznetskiy Alatau mountains: dendrochronolohical reconstruction
Abstract
The outbreaks history of the Siberian moth (Dendrolimus sibiricus Tschetveraikov, 1908) in larch forests of the forest-steppe at the eastern foothills of the Kuznetsk Alatau mountains (West of the Chulym-Yenisei basin, South of Eastern Siberia, Republic of Khakassia) is reconstructed. Outbreaks of this species have repeatedly covered forests from the Urals to the Far East on an area of more than 1 million hectares. However, there is a lack of long series of observations of changes in the size of the Siberian moth populations. Data on the history of the defoliations caused by it will at least partially fill this gap. For reconstruction, we studied the radial growth in six larch stands, which in the past were subjected to intensive defoliation by the Siberian moth. Using the OUTBREAK algorithm, specific features (abrupt, deep, and prolonged declines in growth) were found in the series of radial growth, indicating defoliation in the past. In total 31 such periods were found in 1740–2017. A study of the frequency characteristics of the chronology of defoliation showed that after the end of the Little Ice Age, the interval between defoliations gradually decreased from 10–11 years at the end of the 19th century to 7 years in the 1930s. Since the 1940s, this interval has decreased to 4–6 years, which we attribute to anthropogenic impact (massive logging and, apparently, more frequent ground fires). The consequence of this was the fragmentation of forest stands and the periodic eliminations of overwintering entomophages by fires. As a result, the frequency of occurrence of the Siberian moth foci in the study area increased either due to its escape from the control of entomophages, or because of the formation of a system of migration foci that existed at different times in fragmented forest stands.
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