Abstract
High-elevation forests are among the most climate-sensitive ecosystems, and understanding their growth responses is crucial for predicting ecological consequences under future climate change. The climate sensitivity of tree species in the Hyrcanian forests in the Alborz Mountains of northern Iran, one of the southernmost temperate deciduous forests in the Northern Hemisphere, remains largely unexplored. In particular, Acer hyrcanum Fisch. & C. A. Mey., growing mainly at high elevations, has not yet been studied in detail in dendroclimatology. Here, we present the first tree-ring chronology of Acer hyrcanum spanning 1814–2022 and analyze its growth–climate relationships to assess how this species reflects climatic sensitivity at the upper forest limit. The results reveal significant positive correlations between tree-ring width and temperature, particularly from May to September, suggesting that warmer growing-season temperatures enhance tree growth. In contrast, tree-ring width showed negative correlations with precipitation and standardized precipitation-evapotranspiration index, especially from January to May, and with cloud cover from March to May. These findings suggest that moisture availability does not limit radial growth in Acer hyrcanum and that the precipitation and water surplus signals may instead reflect the influence of cloud cover, which reduces sunlight availability during critical early-season months. This study contributes to the growing body of dendroclimatic research in the Alborz Mountains and, more broadly, on Acer species, particularly in high-elevation ecosystems where such studies are scarce. It also provides valuable insights into how Acer hyrcanum may respond to future climate change.