AimAn increase in conifer mortality has been observed widely across the boreal forest biome. We investigate the causes of this mortality, in addition to the geospatial and temporal dynamics of mortality, in Siberian pine and fir stands.LocationCentral Siberia.Time period1950–2018.Major taxa studiedPinus sibirica Du Tour and Abies sibirica Ledeb.MethodsWe used geospatial analysis of satellite‐derived (MODIS, Landsat) data, topography (elevation, slope steepness and exposure) and climatic variables [precipitation, thermal degree days (TDD = ∑(t > 0 °C), standardized precipitation evapotranspiration index (SPEI) and root zone moisture content (RZM)], together with in situ data. Dendrochronology was applied for analysis of the radial growth increment (GI).ResultsSiberian pine and fir mortality has increased greatly in recent decades. The mortality of forest stands and trees was dependent on the TDD, RZM and SPEI. Mortality occurred mainly within the southern part of the species ranges and decreased northward, correlated with latitudinal gradients of TDD and SPEI. Mortality was observed mostly at elevations < 1,000 m and decreased with increasing elevation, whereas the area of forests and GI of trees increased with elevation. Forest mortality was preceded by the changes in tree GI. Since the onset of climate warming, GI increased until a breakpoint in the mid‐1980s. Further temperature increase caused a reduction in GI owing to moisture stress and division of the tree population into “decliners” and “survivors”. Mortality was caused by the combined impact of moisture stress and bark beetle attacks.Main conclusionSiberian pine and fir mortality was preceded by a reduction in the GI of trees caused by elevated air temperatures, acute droughts and subsequent insect attacks. Forest mortality was observed mostly at low elevations, whereas within the areas with sufficient moisture availability (at elevations c. < 1,000 m) the tree GI and forest area increased. With the projected increase in drought, Siberian pine and fir trees are predicted to retreat from their southern low‐elevation ranges.

Climate impact on landslide occurrence and spatial patterns were analyzed within the larch-dominant communities associated with continuous permafrost areas of Central Siberia. We used high resolution satellite imagery (i.e. QuickBird, WorldView) to identify landslide scars over an area of 62000 km. Landslide occurrence was analyzed with respect to climate variables (air temperature, precipitation, drought index SPEI), and GRACE satellite derived equivalent of water thickness anomalies (EWTA). Landslides were found only on southward facing slopes, and the occurrence of landslides increased exponentially with increasing slope steepness. Lengths of landslides correlated positively with slope steepness. The observed upper elevation limit of landslides tended to coincide with the tree line. Observations revealed landslides occurrence was also found to be strongly correlated with August precipitation (r = 0.81) and drought index (r = 0.7), with June-July-August soil water anomalies (i.e., EWTA, r = 0.68-0.7), and number of thawing days (i.e., a number of days with t > 0°C; r = 0.67). A significant increase in the variance of soil water anomalies was observed, indicating that occurrence of landslides may increase even with a stable mean precipitation level. The key-findings of this study are (1) landslides occurrence increased within the permafrost zone of Central Siberia in the beginning of the 21st century; (2) the main cause of increased landslides occurrence are extremes in precipitation and soil water anomalies; and (3) landslides occurrence are strongly dependent on relief features such as southward facing steep slopes.

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.