Anthropogenic climate change and observed vegetation zone shifts:
Climate determines the distribution of global vegetation zones. In many areas across the globe, the warming, in particular during the last decades, has resulted in shifts of the tree line northwards and to higher altitudes. However, in the European Alps, for example, changes in land use are often more important for the tree line than climate change.
There is also increasing evidence for a global trend towards more drought and heat stress induced tree mortality, in some cases affecting most dominant trees over large areas, in particular in western North America. But, for example, in southern Germany and many areas in the high northern latitudes, climate change had positive effects on vegetation growth.
In some savannah areas, an increasing shrub encroachment has been observed, which might be largely driven by plant-physiological effects of an increasing atmospheric concentration of CO2. This development might generally threaten savannahs and their unique flora and fauna.
As vegetation zone shifts occur with a substantial time-delay and because future climate change will probably be larger than during the recent past, much more substantial shifts should be expected in the future, with pronounced effects on biodiversity, which is often strongly linked with certain vegetation zones.