Climate-Induced Fir (Abies sibirica Ledeb.) Mortality in the Siberian Mountains

Abstract

The mortality of Abies sibirica Ledeb. trees and stands in the Siberian Mountains was analyzed. Fir trees’ growth index (GI) response to warming was two-phased. Since warming onset, the GI was increasing, whereas further air temperature increase caused the GI depression via water stress. Since the GI breakpoint (c. 1983–84), the GI dependence on the moisture increased. Distributions of dead and alive stands with respect to the sum of positive temperatures (Σ(t > 0 °C)), precipitation, root zone moisture and drought index SPEI were different. Mortality of fir stands was strongly increasing with the Σ(t > 0 °C) increase, and it was decreasing with precipitation and root zone moisture increase and atmospheric drought decrease. Stands’ mortality was predisposed by poorer soil moisture within those stands location. Those stands also had initially lower GPP in comparison with the “survived” stands. With respect to relief features, mortality was located mostly on the southeastern slopes, and it was decreasing with elevation increase. Water-stressed fir trees were attacked by bark-beetle Polygraphus proximus Blandford, the bark-beetle that was not observed earlier within the Abies sibirica range. In synergy with water stress, that has led to stands mortality since 2000s. Fir mortality is unprecedented, covered over 5% of fir range and continues to increase. Thus, Abies sibirica is retreating from its low and middle elevation range in the Southern Siberian Mountains.KeywordsTree mortalityConifer declineClimate changePest attacksBark-beetles Polygraphus proximus Drought Abies sibirica Siberian firSiberian taiga