Anthropogenic filtering of flora: diversity loss and biotic homogenization in semi-arid landscapes of Western Iran

This study assesses plant diversity patterns across human-modified (anthropogenic) and natural (refugia) ecosystems in semi-arid southern Hamadan, Iran. Systematic surveys of 200 plots in each habitat documented 304 vascular plant species, with low overlap (only 26% shared). Multivariate and partitioning analyses investigated anthropogenic filtering mechanisms. Results confirm significant local diversity loss in anthropogenic zones, evidenced by lower Shannon diversity (H’Ant = 1.89 vs. H’Nat = 2.35, p =.002) and clear community separation (Permutational Multivariate Analysis of Variance (PERMANOVA), R2 = 0.37, p < .001). Endemic species were particularly vulnerable, showing a 59.7% reduction in disturbed habitats. Beta Diversity Partitioning identified nestedness (βsne) as the core mechanism of change, significantly higher in anthropogenic areas (βsne = 0.21 vs. βsne = 0.12), indicating biotic homogenization driven by systematic species loss. Filtering resulted in pronounced lifeform shifts, including a 3.2-fold decline in geophytes and a dominance of ruderal annuals. Natural areas serve as critical refugia for Irano-Turanian endemics. This study provides crucial baseline data for conservation planning to mitigate floristic homogenization in semi-arid ecosystems.