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The characteristics of Abies sibirica Ledeb.- and Pinus sibirica Du Tour dominated forests stands in outbreak spots formed during a Dendrolimus sibiricus outbreak in 2014–2017 were studied at the stage of population collapse (east of the West Siberian Plain and western foothills of the Yenisei Range). The research was based on the data obtained during ground surveys conducted in 2016 when stands characteristics, the Siberian silk moth population density, and defoliation level were recorded. We classified the studied stands using decision trees and random forest algorithms to identify the key characteristics that determine the formation of outbreak spots. The classification results showed that the characteristics of the detected outbreak spots differ significantly from those previously described for dark coniferous stands of the southern taiga in Siberia. The highest probability of the outbreak spot occurrence in the study area was revealed for stands with the following characteristics: moderately moist site; Siberian stone pine and Siberian fir take 40% or more of stem volume; age of less than 105 years. Another group of forest stands under threat are those sharing the following characteristics: large area (more than 60 ha); stand homogeneity; ground vegetation is dominated by feather mosses; age of more than 120 years; Picea obovata Ledeb. takes a significant share in a stem volume. Such characteristics indicate that during the population collapse, the Siberian silk moth forms outbreak spots in stands that either undergo an early successional stage after previous outbreak or have been slightly damaged during the previous outbreaks due to unfavorable habitat conditions.

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The paper investigates changes in the species structure of forests over a 20-year period (2001-2020) for the zone of the alleged flooding of the Nizhneboguchanskaya HPP and adjacent areas using geographic information systems and Earth remote sensing data. Areas of forest destroyed as a result of felling and fires were identified. The paper gives a quantitative estimation of these changes. A map of the dominant tree species for the study area was obtained. The satellite imagery of medium spatial resolution (Sentinel, Landsat) was used as the initial data, as well as information products Burned Area and Forest Cover Loss of the University of Maryland based on satellite data and field research data. It was found that the number of coniferous plantations in the study area decreases. On the contrary, the proportion of non-forested areas as well as deciduous species increases.