Slope mediates growth-climate response of Pinus wallichiana in central Nepal

Abstract

The Himalayas are the most vulnerable regions to climate change, and they have been experiencing diverse impacts on mountain vegetation. Blue Pine (Pinus wallichiana) is an evergreen conifer which grows at altitudes of 1800–4300 m in dry valleys in Nepal Himalaya. We carried out a dendroecological study to examine growth-climate response of P. wallichiana on contrasting topography—relatively moist North facing and dry South facing slopes. Tree-ring width indices exhibited a significant positive correlation with the previous year’s September rainfall and negative correlation with the current year maximum temperature of June. The Basal Area Increment (BAI) generally showed a positive trend, however, both sites showed declining trends of BAI particularly after the 1980s, with a more pronounced decrease observed on the south-facing slope. This may be due to changes in topographic conditions due to slope exposure; higher evapotranspiration, strong wind and lower moisture supply due to low runoff from snow melting in the southern slope. However, we emphasize that responses from similar aged tree populations should be validated using more precise local climatic data to improve the interpretation of microclimate-driven growth-climate relationships and to strengthen climate adaptation strategies for Himalayan forests. Nonetheless, the results underscore the role of topographic variability in shaping forest sensitivity to climate, highlighting the importance of slope-specific considerations in forest management and adaptation strategies in Himalaya.