Climate induced birch mortality in Trans-Baikal lake region, Siberia

Abstract

a b s t r a c tThe Trans-Baikal (or Zabailkal'e) region includes the forest-steppe ecotones south and east of Lake Baikal in Russia and has experienced drought for several years. The decline and mortality of birch (Betula pendula) stands within the forest-steppe ecotone Trans-Baikal region was studied based on a temporal series of satellite data, ground measurements, and tree ring analysis. During the first decade of the 21st century birch stands decline and mortality were observed on about 5% of the total area of stands within our 1250 km 2 study area. Birch forest decline and mortality occurs mainly at the margins of stands, within the forest-steppe ecotone on slopes with direct insolation. During the first decade of the 21st century summer (June-August) precipitation was about 25% below normal. Soil water content measurements were lowest within dead stands and highest within healthy stands and intermediate within damaged stands. Drought impact on stands was amplified by an increase in summer air temperatures (+0.9°C) in comparison with the previous decade. Tree ring data of ''surviving'' and ''dead'' tree groups showed a positive correlation with summer/annual precipitation and negative correlation with summer air temperatures. Temperature and precipitation extreme anomalies tend to occur in the region with a period of about 27 years. The observed anomaly was the most severe since the beginning of meteorological observations in the year 1900. Data for the other sites showed a positive climate impact on the growth and expansion of Siberian forests. That is, the same species (B. pendula) showed considerable increase (1.4 times both in height and stem volume) during 20th-21st centuries as temperature increased but precipitation remained at adequate levels.

Simulating Changes in Fires and Ecology of the 21st Century Eurasian Boreal Forests of Siberia

“…Application of the drought-triggered fire regime to simulation of potential future climate based on linear extrapolation of observed warming ( Figure A1d) in the region along the southern boundary of the boreal zone results in greater incidence of drought, both on the south-facing slope and at lower elevations along north-facing slopes. Under this warming scenario, vegetation shifts upslope on both aspects, and the ribbon forests on the south-facing slopes decrease in vigor and biovolume, which is in accordance with observations [38,39,85] and previous modeling studies [47,86]. Warming ambient temperatures increase the PET demands on vegetation, but if no concurrent increase in precipitation occurs, vegetation becomes stressed and either dies from temperature-based drought stress or more easily succumbs to mortality from insects, fire, pathogens, or windthrow.…”

On underestimation of global vulnerability to tree mortality and forest die‐off from hotter drought in the Anthropocene

“…Further, warmer temperatures in the absence of significant drought have been shown to increase tree growth rates, particularly in deciduous species (Way and Oren 2010). Overall, the direct mortality consequences of warming could be relatively small and limited when considered globally, as earth system feedbacks (e.g., greater atmospheric moisture and precipitation) combined with multiple treelevel compensatory processes can buffer future Xiong et al 2011, Kharuk et al 2013, Zhang et al 2014b, Zhou et al 2013, 2014bAustralasia, Semple et al 2010; Europe,Čater 2015; North America, Vogelmann et al 2009, Zegler et al 2012, Baguskas et al 2014, Hart et al 2014, Kane et al 2014, Twidwell et al 2014, Gu et al 2015South America, Brienen et al 2015. v www.esajournals.org tree mortality relative to hotter droughts (e.g., Klein et al 2014a).…”

Rapid warming accelerates tree growth decline in semi‐arid forests of Inner Asia

“…Increasingly frequent and severe drought events also have been observed in northern and eastern Inner Asia in recent decades (Li et al ., ; Sheffield et al ., ). In addition, we and others (Kharuk et al ., ) have observed recent tree mortality in low‐elevation temperate and southern boreal forest regions distributed close to the xeric treeline in Asia. We hypothesize that recent warming has caused reduced tree growth in relatively arid regions near the xeric treeline in Inner Asia.…”