Impacts of environmental change on biodiversity and vegetation dynamics in Siberia.

Biological diversity is the basis for, and an indicator of biosphere integrity. Together with climate change, its loss is one of the two most important planetary boundaries. A halt in biodiversity loss is one of the UN Sustainable Development Goals. Current changes in biodiversity in the vast landmass of Siberia are at an initial stage of inventory, even though the Siberian environment is experiencing rapid climate change, weather extremes and transformation of land use and management. Biodiversity changes affect traditional land use by Indigenous People and multiple ecosystem services with implications for local and national economies. Here we review and analyse a large number of scientific publications, which are little known outside Russia, and we provide insights into Siberian biodiversity issues for the wider international research community. Case studies are presented on biodiversity changes for insect pests, fish, amphibians and reptiles, birds, mammals and steppe vegetation, and we discuss their causes and consequences.

Wildfires in the Siberian taiga.

The majority of area burned by wildfire are located in Siberia. Mainly low-intensity surface fires occur in larch forests, whereas in evergreen forests both surface and crown fires are observed. Warming has led to an increase in the frequency and area of wildfires that have reached the Arctic Ocean shore. However, wildfires are the most important factor in taiga dynamics; larch and Scots pine have evolved under conditions of periodic forest fires, thereby gaining a competitive advantage over non-fire adapted species; in the permafrost zone, periodic fires are a prerequisite for the dominance of larch. Wildfires support ecosystem health, biodiversity, and conservation; periodic wildfires decrease the danger of catastrophic wildfires. With an amplified rate of increase in fires, it is necessary to focus fire suppression on areas of high social, natural, and economic value, while allowing a greater number of wildfires to burn in the vast Siberian forest landscapes.

Climate-induced mortality of Siberian pine and fir in the Lake Baikal Watershed, Siberia.

Siberian pine (Pinus sibirica) and fir (Abies sibirica) (so called "dark needle conifers", DNC) showed decreased radial growth increment within the Lake Baikal watershed since the 1980s with increasing mortality recorded since the year 2000. Tree ring width was strongly correlated with vapor pressure deficit, aridity and root zone moisture. Water stress from droughts made trees more susceptible to insect attacks causing mortality in about 10% of DNC stands within the Lake Baikal watershed. Within Siberia DNC mortality increased in the southern part of the DNC range. Biogeographically, tree mortality was located within the DNC - forest-steppes transition. Tree mortality was significantly correlated with drought and soil moisture anomalies. Within the interior of the DNC range mortality occurred within relief features with high water stress risk (i.e., steep convex south facing slopes with shallow well-drained soils). In general, DNC mortality in Siberia was induced by increased aridity and severe drought (inciting factors) in synergy with biotic attacks (contributing factor). In future climate scenarios with predicted increase in aridity DNC could be eliminated from the southern part of its current range and will be replaced by drought-resistant conifers and broadleaf species (e.g., Larix sibirica, Pinus silvestris, and Betula pubescence).

Climate-Induced Northerly Expansion of Siberian Silkmoth Range.

Siberian silkmoth (Dendrolimus sibiricus Tschetv.) is a dangerous pest that has affected nearly 2.5 × 106 ha of "dark taiga" stands (composed of Abies sibirica, Pinus sibirica and Picea obovata) within the latitude range of 52°-59° N. Here we describe a current silkmoth outbreak that is occurring about half degree northward of its formerly documented outbreak range. This outbreak has covered an area of about 800 thousand ha with mortality of conifer stands within an area of about 300 thousand ha. The primary outbreak originated in the year 2014 within stands located on gentle relatively dry southwest slopes at elevations up to 200 m above sea level (a.s.l.) Then the outbreak spread to the mesic areas including northern slopes and the low-elevation forest belts along the Yenisei ridge. Within the outbreak area, the northern Siberian silkmoth population has reduced generation length from two to one year. Our study showed that the outbreak was promoted by droughts in prior years, an increase of the sum of daily temperatures (t > +10 °C), and a decrease in ground cover moisture. Within the outbreak area, secondary pests were also active, including the aggressive Polygraphus proximus bark borer beetle. The outbreak considered here is part of the wide-spread (panzonal) Siberian silkmoth outbreak that originated during 2014-2015 with a range of up to 1000 km in southern Siberia. Our work concludes that observed climate warming opens opportunities for Siberian silkmoth migration into historically outbreak free northern "dark taiga" stands.

Tree Wave Migration Across an Elevation Gradient in the Altai Mountains, Siberia.

The phenomenon of "tree waves" (hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine (Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. Time series of high-resolution satellite scenes (from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 155±26 m (or 3.7 m yr-1) and crown closure increased (about 35-90%). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the "ribbon zone" was approximately 2.5 times (5060 vs 2120 ha-1) higher then within the "hedges zone". During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment and recent tree growth rate for 50 year old trees was about twice higher than recorded for similarly aged trees at the beginning of the 20th century. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains.

Larch Forests of Middle Siberia: Long-Term Trends in Fire Return Intervals.

Fire history within the northern larch forests of Central Siberia was studied (65+°N). Fires within this area are predominantly caused by lightning strikes rather than human activity. Mean fire return intervals (FRI) were found to be 112 ± 49 years (based on fire scars) and 106 ± 36 years (based on fire scars and tree natality dates). FRI were increased with latitude increase, and observed to be about 80 years at 64°N, about 200 years near the Arctic Circle, and about 300 years nearby the northern range limit of larch stands (~71°+N). Northward FRI increase correlated with incoming solar radiation (r = - 0.95). Post Little Ice Age (LIA) warming (after 1850) caused approximately a doubling of fire events (in comparison with a similar period during LIA). The data obtained support a hypothesis of climate-induced fire frequency increase.

Climate-Induced Landslides within the Larch Dominant Permafrost Zone of Central Siberia.

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 km2. 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 tmax > 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.