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Aim: An 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. Location: Central Siberia. Time period: 1950–2018. Major taxa studied: Pinus sibirica Du Tour and Abies sibirica Ledeb. Methods: We 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). Results: Siberian 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 conclusion: Siberian 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. [ABSTRACT FROM AUTHOR]

Larch-dominant communities are the most extensive high-latitude forests in Eurasia and are experiencing the strongest impacts from warming temperatures. We analyzed larch (Larix dahurica Turcz) growth index (GI) response to climate change. The studied larch-dominant communities are located within the permafrost zone of Northern Siberia at the northern tree limit (ca. N 67° 38′, E 99° 07′). Methods included dendrochronology, analysis of climate variables, root zone moisture content, and satellite-derived gross (GPP) and net (NPP) primary productivity. It was found that larch response to warming included a period of increased annual growth increment (GI) (from the 1970s to ca. 1995) with a follow on GI decline. Increase in GI correlated with summer air temperature, whereas an observed decrease in GI was caused by water stress (vapor pressure deficit and drought increase). Water stress impact on larch growth in permafrost was not observed before the onset of warming (ca. 1970). Water limitation was also indicated by GI dependence on soil moisture stored during the previous year. Water stress was especially pronounced for stands growing on rocky soils with low water-holding capacity. GPP of larch communities showed an increasing trend, whereas NPP stagnated. A similar pattern of GI response to climate warming has also been observed for Larix sibirica Ledeb, Pinus sibirica Du Tour, and Abies sibirica Ledeb in the forests of southern Siberia. Thus, warming in northern Siberia permafrost zone resulted in an initial increase in larch growth from the 1970s to the mid-1990s. After that time, larch growth increment has decreased. Since ca. 1990, water stress at the beginning of the vegetative period became, along with air temperature, a main factor affecting larch growth within the permafrost zone. [ABSTRACT FROM AUTHOR]