Conifer Growth During Warming Hiatus in the Altay-Sayan Mountain Region, Siberia

Abstract

“Warming hiatus” occurred in the Altay-Sayan Mountain Region, Siberia, in c. 1997–2014. We analyzed evergreen conifer (EGC: Pinus sibirica du Tour and Abies sibirica Ledeb. mainly) stands area (satellite data) and trees (Pinus sibirica, Larix sibirica Ledeb.) growth response to climate variables before and during the hiatus. During the hiatus, the EGC area increased in highlands (+30%), whereas at lower elevations (<1000 m a.s.l.), the area decreased (−7%). In highlands, the EGC area changes correlated with summer air temperature mainly, whereas at lower elevations, the changes correlated with drought index SPEI. EGC mortality (Siberian pine and fir mainly) in lowland was caused by the synergy of water stress (inciting factor) and bark-beetle attacks (contributing factor). Within alpine forest–tundra ecotone (2000–2280 m), the larch growth index (GI) was limited by air temperature, whereas the Siberian pine GI was also sensitive to precipitation, root zone moisture content (RZM) and sunshine duration. Warming led to transformation of krummholz Siberian pine into vertical form, whereas larch had vertical forms before warming. Within high elevation belt (1200–2000 m), the Siberian pine growth index (GI) permanently increases since warming onset; the GI positively responded to June–July temperatures and negatively responded to moistening parameters (precipitation, root zone moisture content, and SPEI). At middle elevation, the Siberian pine GI curve has a breakpoint (c. 1983) followed by GI depression. After the breakpoint, the GI correlation with air temperature switched from positive to negative. At the same time, positive correlations between the GI and “moisture parameters” (precipitation, RZM, SPEI) increased. Under projected climate change scenario, Siberian pine will shrink its habitat at middle and low elevations with substitution by drought-resistant larch and softwoods species.