Impact of climate change on the distribution range and niche dynamics of Himalayan birch, a typical treeline species in Himalayas

Globally, treeline in mountain landscapes is reported to be sensitive to projected warming by climate change. Betula utilis (Himalayan birch), a principal tree species defining the natural treeline in Himalayas, is a potential indicator species to track the signal of climate change. The present study models the ensemble distribution of B. utilis using Biomod2 package for present and future (RCP's 2.6-8.5 covering 2050 and 2070). The final ensemble model obtained had AUC=0.886 and TSS=0.655, thus indicating robustness of the model. We assessed change in the habitat suitability, area expansion and contraction based on ensemble model using SDM Toolbox. The highly suitable area for B. utilis is predicted to shift towards the eastern parts of Himalayas in future, with suitability declining towards the western part of Himalayas. The study, to our best knowledge, for the first time used Ecospat package to assess niche dynamics (i.e. overlap, similarity and equivalency) of B. utilis, which predicted the climatic niche of this treeline species is moderately shifting in future scenarios. Further, the PCA analysis indicated that significant variation (33.45% on PC1 and 24.63% on PC2) exists in the climatic conditions between current and future scenarios. The similarity and equivalency test revealed that B. utilis niche is similar but not identical between current and future climate change scenarios. Hopefully, the results from the present study will contribute significantly in understanding the impacts of climate change in Himalayas with wide implications for scientifically-informed adaptation and mitigation strategies.