In many mountain regions, multiple sources of evidence point to tree expansions into treeless areas above  the forest belt. This may increase forest productivity at the upper treeline. Treelines have moved up in the last 30-100 years in many mountain regions, including, for example, the Andes, Urals and Altai. At the same time, since the 1990s, treeline responses in different parts of the Himalaya have been highly variable, in some places advancing upslope, in others demonstrating little change and in yet others moving downwards. This can be explained by site-specific complex interactions of the positive effects of warming on tree growth, drought stress, change in snow precipitation, land use change, especially grazing, and other factors. Treelines are affected by land use and management around the globe, and changing land use practices can supersede climate change effects in some mountain regions. An upward shift in the elevation of bioclimatic zones, decreases in the area of the highest elevation zones and an expansion of the lower zones can be expected by mid-century, for example in regions such as the Himalaya.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report