The impact of warming climate on Himalayan silver fir growth along an elevation gradient in the Mt. Everest region

The impacts of rapid climate change in the Himalayan region on growth and sensitivity of tree species across their entire elevation distribution range are not well understood. This study investigates the growth and climate sensitivity of the endemic species Himalayan silver fir (Abies spectabilis, D.Don) along an elevation gradient in the sub-alpine belt in the Mt. Everest region. We developed tree ring-width chronologies, spanning 98 to 310 years, from six sites along an elevation gradient (3400-4100 m a.s.l.). The growth of Himalayan silver fir is primarily limited by low temperatures during the growing season and moisture availability during spring. Significant positive correlations were found between tree growth and mean, minimum and maximum temperatures for most parts of the vegetation period except spring. In contrast, significant positive correlations are apparent for pre-cipitation, self-calibrated Palmer drought severity index (scPDSI), and standardized precipitation-evapotranspiration index (SPEI) during the spring season (March-May) at most of the elevations except for the upper treeline site. Thus, low summer temperatures are the primary limiting factor at all investigated ele-vations, while moisture supply during spring triggers growth variations at low-to mid-elevations. The long-term growth trends of A. spectabilis have decreased at low-to mid-elevation sites but increased at the treeline during the period 1981-2011. Warming and intensified moisture stress during spring could have negative effects on tree growth, potentially resulting in growth decline and forest dieback at middle and low elevations. These findings emphasize the importance of understanding the vulnerability of forests at middle and low elevations to future climate change.