Projecting future climatic refugia for Fagus orientalis in the Hyrcanian ecoregion

Ongoing changes in temperature and precipitation regimes are altering the climatic suitability of temperate tree species, particularly at their southern distribution margins. In the Hyrcanian forests of northern Iran, Oriental beech ( Fagus orientalis ) plays a central structural and ecological role, yet its future persistence under climate change remains uncertain. We assessed current habitat suitability and projected range dynamics using an ensemble species distribution modeling framework integrating Random Forest, Support Vector Machine, MaxEnt, and Boosted Regression Trees. Nineteen bioclimatic variables were screened for collinearity and calibrated against 1,092 spatially filtered occurrence records. Future projections were generated for mid-century (2041–2060) and late-century (2061–2080) under SSP1-2.6 and SSP5-8.5 scenarios using a five-GCM CMIP6 ensemble. Model performance was high (AUC > 0.88; TSS > 0.67). Precipitation Seasonality (Bio15) was identified as the dominant predictor (mean contribution 52%), suggesting that intra-annual rainfall variability is a key constraint at the species’ southern range margin. Projections indicate a progressive contraction of climatically suitable habitat. Under SSP1-2.6, suitable area declines by approximately 73% by mid-century, whereas under SSP5-8.5, reductions reach up to 96% by late century. Suitable habitat becomes increasingly fragmented and concentrated in western Hyrcanian forests, particularly in Gilan and western Mazandaran. These results suggest a substantial contraction of climatically suitable habitat for F. orientalis , although realized distributions may persist longer due to demographic inertia and long tree lifespans. Protecting climatically buffered western refugia and incorporating adaptive forest management strategies will be important to support long-term ecosystem stability in these relict temperate forests.