Plant community responses to climate change in the Zayandeh-Rud Basin, Iran: Does woody plant encroachment follow global patterns?

Arid and semi-arid ecosystems are highly sensitive to climate warming and drying, yet community-level responses in the Middle East remain poorly quantified. This study assesses the potential impacts of climate change on plant community distributions in the Zayandeh-Rud basin, central Iran, and evaluates whether woody plant encroachment follows global patterns. Species distribution models were applied to project current and future (2050 and 2070) distributions of major vegetation communities, including Semi Steppe-Shrub, Semi Steppe-Perennial Herbaceous, Alpine Vegetation, Semi Desert-Salty Plants, Semi Desert-Shrub, Semi Steppe-Semi Shrub, and Steppe-Semi Shrub, under three climate scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). Annual precipitation (Bio12) was identified as the primary driver shaping Semi Steppe-Shrub, Semi Steppe-Perennial Herbaceous, Semi Steppe-Semi Shrub, and Steppe-Semi Shrub communities, whereas maximum temperature of the warmest month (Bio5) and slope were influential predictors for Alpine Vegetation and semi-desert communities. In the study area, the mean (± SD) of GCMs and SSPs for the net change percentage of total woody plant communities (including Semi Steppe-Shrub, Semi Steppe-Semi Shrub, Steppe-Semi Shrub, and Semi Desert-Shrub) during the period 2050 to 2070 (over the next 60 years) was estimated at 26.86 ± 12.05%. The annual expansion rate of these woody communities was estimated at 0.45 ± 0.20%. These patterns suggest a potential trend of woody plant encroachment that may be associated with increasing temperatures and declining precipitation. Such structural changes may lead to increased dominance of woody species, shifts in community composition, biotic homogenization, and potential impacts on ecosystem functions, including carbon sequestration, nutrient cycling, soil stability, and biodiversity conservation.