No abstract

This research is dedicated to solving an urgent problem associated with the large-scale destruction of taiga forests by Siberian silk moth (Dendrolimus sibiricus) outbreaks. The dynamics of the damage to dark coniferous forest stands induced by the Siberian silk moth outbreaks in mid-altitude mountains were studied. A hypothesis was formulated based on the fundamental influence of the orography on the phytophage’s dispersal within the landscape, along with the climate, which acts as a secondary predictor—a catalyst for outbreaks. The study was carried out using Landsat−8 satellite imagery time-series (from 2018 to 2020). The data were verified using a field forest pathological survey of the territory. An assessment of the defoliated forest area and damage association with the landscape was carried out using an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model. The assessment was aimed to detail the forecast parameters for an outbreak development in mid-altitude mountains using the orographic features—altitude, terrain slope, and slope aspect. Early warnings of phytophagous insect outbreaks in mountain southern taiga should be focused on the permanent monitoring of dark coniferous stands of the mossy group of forest types, covering altitude levels from 400 to 600 m, located on gentle terrains and slopes of up to 15 degrees. The greatest vulnerability to phytophage impacts was characterized as areas located at altitudes from 400 to 600 m. The upper limit of D. sibiricus distribution was 900 m above sea level. The results obtained provide comprehensive information on the Siberian silk moth potential reserves within the study area with the possibility of extrapolation to similar territories. The data will make it possible to model pest outbreaks based on orography and improve the forest pathological monitoring methods at the regional level.

Анализировались индекс радиального прироста (ИП) Abies sibirica Ledeb. и динамика массового усыхания пихтовых древостоев в горных лесах Восточного Саяна (заповедник "Столбы"). Беспрецедентное по масштабам усыхание пихты оказалось спровоцировано водным стрессом, обусловленным возрастанием температуры воздуха, в синергизме с воздействием уссурийского полиграфа (Polygraphus proximus Blandford), ксилофага, ранее не наблюдавшегося в ареале Abies sibirica.В начальной фазе потепления климата наблюдалось возрастание ИП, сменившееся его депрессией в 1985-2017 гг. Усыханию пихтарников предшествовало усиление зависимости ИП от индекса сухости SPEI и влажности корнеобитаемого слоя (ВКС). При этом ИП когорты усохших деревьев сильнее зависел от ВКС (r 2 = 0,56) и SPEI (r 2 = 0,74), чем ИП когорты выживших деревьев (r 2 = 0,15 и r 2 = 0,39 соответственно).Усыхание пихты началось в 2000-х гг., когда ослабленные водным стрессом пихтарники подверглись атаке уссурийского полиграфа. В этот период погибшие древостои локализовались преимущественно на элементах рельефа с наибольшей вероятностью водного стресса (крутые склоны, расположенные в "дождевой тени"). К 2017 г. усыхание распространилось на всю территорию пихтарников, что привело к гибели ~75 % древостоев. В данный период наблюдалась тесная связь ИП со смертностью деревьев пихты (r = -0,79). Выжившие деревья по сравнению с усохшими произрастали в условиях более высокой влажности корнеобитаемой зоны. Примечательна близость траекторий ИП когорт усохших и живых деревьев, что указывает на вероятность гибели живых деревьев в условиях прогнозируемого возрастания засушливости климата.

The present study attempts to identify the biological characteristics of invasive (high-impact in the secondary area) bark beetles and borers species, contributing to their success in an invaded area. We selected 42 species based on the CABI website data on invasive species and information on the most studied regional faunas. Four groups of species with different invasion strategies were identified based on the cluster and factor analysis. The first one (inbred strategy) is characterized by flightless males, xylomycetophagy, low fecundity (~50 eggs), inbreeding, polyvoltinism, and polyphagy. Species with an aggressive strategy are poly- or monovoltine, feeds on a limited number of hosts, larval feeding on the inner bark, are often associated with phytopathogens, and produce aggregation pheromones. Representatives of the polyphagous strategy have a wide range of hosts, high fecundity (~150 eggs), larval feeding on wood, and their life cycle is at least a year long. For the intermediate strategy, the typical life cycle is from a year or less, medium fecundity, feed on inner bark tissues, mono- or oligophagy. Comparison with low-impact alien species showed that the most significant traits from the viewpoint of the potential danger of native plant species are high fecundity, polyvoltinism, presence of symbiotic plant pathogens, long-range or aggregation pheromones.