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 identify the climatic treeline — the potential upper limit of forests determined by climatic conditions — in the Carpathian Mountains, one of Europe’s largest contiguous forest ecosystems. We downscale climate variables to a 30-m resolution by applying a polynomial approximation to the regression residuals, incorporating terrain attributes. We then correlate climatic variables with the location of the climatic treeline. The mean temperature of the warmest quarter demonstrates the strongest correlation with treeline location. We find a total area of 1,370 km 2 above the current climatic treeline in the Carpathians, which constitutes the climatic envelope for alpine ecosystems. Depending on future climate projections, this area will decrease to 410–515 km 2 by 2040, 100–320 km 2 by 2060, and 15–290 km 2 by 2080. The anticipated upward shift of the treeline jeopardizes the region's rare and endemic alpine species and has substantial ramifications for ecosystems, water balance, and the carbon cycle in the Carpathian Mountains. Our analysis highlights the importance of understanding how climate affects treeline locations for effective ecosystem management and conservation planning in a changing climate.