Vulnerability of Norway spruce to climate change in mountain forests of the European Alps

Mountain forests offer a range of socio-economic and ecological services, e. g. providing wood harvest products, serving as hotspots of biodiversity and fulfilling protective functions. In the European Alps, where these environments are dominated by drought-sensitive Norway spruce, it has been questioned whether these services can be secured in the substantially warmer and drier climates predicted for the mid-to-late 21st century. Here, we compile a tree-ring width network of 500 spruce trees from the Northern Limestone Alps to assess growth reactions to drought events and evaluate the long-term impact of the recent temperature shift through ana lyses along elevational transects. Our dataset covers a larger region in the Northern European Alps extending 250 km from west to east and encompassing an altitudinal range of 1200 m (from 500 to 1700 m a.s.l.). Climate-growth analyses reveal spatially varying drought sensitivities within this spruce network, with elevation (along with associated hydrothermal changes) being the key drivers behind the varying responses. Trees at lower elevations are affected negatively by drought and high temperatures, but at higher altitudes, spruce benefits from warmer climatic conditions. However, despite a sharp temperature increase of similar to 1 degrees C since the 1990s, we observed neither growth suppression at the lower elevation sites nor growth increase at higher elevation sites. These findings reveal the ability of mountain forests to adapt to an unprecedented temperature shift, suggesting that adaptation to forthcoming climate changes might not require a shift in tree species composition in the Northern Limestone Alps.