The emergence and spread of non-native invasive forest insects represent a major potential threat to global biodiversity. The present study examines the current invasion of the far eastern four-eyed fir bark beetle Polygraphus proximus Blandf. in southern Siberian fir (Abies sibirica Ledeb.) forests. We collected data on 38 large sized (2500 m²) sample plots, situated in fir forests of the Tomsk region. As a direct result of the four-eyed fir bark beetle infestation, stand density decreased by 34-37%, and stand volume by 30%. The mean height, individual age and diameter at the stand level consequently increased. Our results indicated that stands with complete left-sided or normal ontogenetic structure (composed primarily of late virginal firs or firs in young reproductive stage) are more resistant to invasion by the four-eyed fir bark beetle. By contrast, fir forests characterized by more right-sided ontogenetic structure (composed primarily of mature and old reproductive firs), exhibited the least resistance and, with rare exception, degraded rapidly in response to the invasion. Our results also pointed to a mechanism that initiates invasions of the four-eyed fir bark beetle in fir stands of all types of ontogenetic structure, which is the attack of virginal trees and trees in early reproductive stages. Trees up to average diameter are the most susceptible to invasions of the bark beetle. We identified thicker bark, larger DBH and low occurrence of heart rot as the most important parameters for indicating resistance at the single tree level. DBH and bark thickness (p<0.05) correlated significantly with tree health status in infested stands. Our overall assessment of the potential natural regeneration of damaged stands is that the Siberian fir forests are resilient to invasive species and that the fir ecosystems can potentially recover from this disturbance.

This study assessed the potential of natural regeneration (NR) of forests in Western Siberia, dominated by Siberian fir (Abies sibirica Ledeb.) and damaged due to the invasion of the four-eyed fir bark beetle (Polygraphus proximus Blandf.). The leading methods for investigating this problem are the sample plot method and the transect method, which allow revealing the features of NR, their morphological structure and spatial distribution. Analysis of the occurrence and structure of NR revealed a correlation between the degree of stand damage and sapling state. The spatial structure was highly heterogeneous, testifying the group location of NR and the variable density. For 63% of the sample plots, a decrease in saplings was recorded as a result of the impact of the four-eysouthern ed fir bark beetle. Most of the dead saplings were large (95%), and dead saplings accounted for 10–50%. A positive correlation was found between the decrease in saplings and the state of the fir forest. The number of saplings varied from 1,233 to 19,200 plants ha−1, with fir being the dominant species. Fir forests of Western Siberia, damaged by the four-eyed fir bark beetle, have the potential for regeneration.

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Under natural conditions, Siberian pine Pinus sibirica begins to produce commercial cone yields of nuts relatively late (after more than 100 years). The aim of this study was to summarise the experience of the directed formation of Siberian pine forests in Siberia. Experimental objects included plots with traditional thinning of varying intensity and frequency as well as chemical treatment. We assessed the parameters of the stand and its seed production dynamics. Only stands with a minimum density (395–435 trees·ha–1) had a normal seed production energy (1.5 or more cones per shoot). Over-dense stands (830–930 trees·ha–1) were characterised by a low seed production energy (two times or more below the threshold value). In all plots, there were Siberian pine trees with absent or unacceptable seed production energy, which should be removed (DBH up to 28 cm). Seed production energy positively correlated with most tree parameters (age, height, diameter, volume, length and width of crown).

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