Global climate change due to elevated temperature and warming induced drought during the past century has become the critical issue for the growth dynamics and productivity of forest ecosystems. High Mountains of the Himalayas are warming at an alarming rate higher than the global average, so, the growth and productivity of high-elevation Himalayan forests are globally concerned. Better understanding on the growth dynamics and growth-responses of Himalayan montane forests to the climate variability could help to anticipate current and future changes in growth dynamics of high-elevation forest ecosystems. However, the growth-responses of high-elevation Himalayan montane forests with present and upcoming climatic variability under different site conditions and along elevation gradients in the current scenario of global climate changes is poorly understood and thus needs to be investigated. In this study, we aimed to reveal the growth-responses of high-elevation Himalayan fir (Abies spectabilis) forests along elevation gradients covering an entire altitudinal distribution range from 2800 to 3900 m asl under semi-arid and humid site conditions in the central Himalaya, Nepal. We used tree-ring analyses, and computed bootstrapped static and 30-year moving correlation analyses to detect the changes in tree growth-responses with the changing climate under contrasting site conditions.
Results/Conclusions
High-elevation Himalayan fir forests showed similar growth responses along elevation gradients in both semi-arid and humid sites. The tree-growth along elevation gradients of each site is tele-connected to the common environmental forcing. Tree-growth of Himalayan fir forests showed negative correlation with spring and early-summer temperatures in the semi-arid site, and the negative correlation was most pronounced and consistent with May temperatures. Moreover, the tree-growth showed positive relationship with spring and early summer precipitation and moisture availability. Meanwhile, shift in negative/positive correlation towards the early springs with temperatures/precipitation have been noticed since the beginning of 1970s. Similarly, in the humid site, tree-growth showed positive correlation with summer temperatures (mainly that of August). Surprisingly, growth-response become reversed and showed negative relationship to the elevated pre-monsoon and early summer temperatures since early 1970s. The elevated temperatures may increase evapotranspiration causing water deficit on tree-growth of high-elevation forests in the Himalayan Mountains. Our results provide the evidence that high-elevation montane forests in the Himalayas are being more vulnerable to elevated temperatures not only in the semi-arid sites, even in the humid site since early 1970s due to the global climate changes.