Climatic determinants of the Carpathian treeline and its projected upward shifts in response to climate change

Treelines represent a significant ecological boundary in mountainous regions. Changes in temperature and precipitation regimes due to climate change affect the location of treelines, contingent on fine-scale variations in orographic and climatic conditions. Using high-resolution satellite imagery, we identified climatic treelines in the Carpathian Mountains, one of Europe’s largest contiguous forest ecosystems. We downscaled climate variables to a 30-meter resolution through a polynomial approximation of regression residuals with terrain attributes, then correlated climatic variables with the location of the climatic treeline. Growing degree days above 5°C demonstrated the strongest correlation with treeline location. Our growing degree threshold results in a total area of 1,370 km ² above the current climatic treeline in the Carpathians. This area constitutes the climatic envelope for alpine ecosystems and comprises the highest ridges and peaks. Using future climate projections, this area will likely decrease to 410–515 km ² by 2040, 100–320 km ² by 2060, and 15–290 km ² by 2080. The upward shift threatens the region's rare and endemic alpine species and will trigger substantial ramifications for ecosystems, water balance, and the carbon cycle in the Carpathian Mountains. A better understanding of the effects of climate change on treeline locations is crucial for informing ecosystem management and conservation planning, as well as to cushion the impacts of climate change on agriculture and forestry practices.