摘要：This study aimed to investigate the effects of different climatic conditions (arid vs. semi-arid) on patterns of species richness and plant diversity as well as plant composition in two over-grazed regions. The regions were located in the west of Iran, closed to each other and different in climatic conditions. Based on the aridity index of De Martonne climate classification, Rika (I = 9.94) and Dalab (I = 18.54) were categorized as arid and semi-arid regions, respectively. In each region, we collected plant vegetation data from a nested sampling design consisted of local (80 plots) and regional (8 sites) scales. Patterns of plant diversity and species richness in each region, and similarity of plant composition between the two regions were analyzed using multiplicative partitioning methods, species richness estimator and cluster analysis, respectively. The results showed that diversity components in all scales had significant difference with their expected values (P<0.000) resulted in non-random distribution of plant species among and within scales. In addition, the results showed that species richness in Rika region (arid, 89 species) was greater than Dalab region (semi-arid, 76 species). The results of cluster analysis suggested that Rika and Dalab regions had different plant species compositions. Based on our results, the role of seed dispersal might be more prominent in smaller scales (plot and sites) compared to region scale, since the highest possible amount of β-diversity was occurred between regions. Our results suggested that plant diversity in the largest scale (region) had the highest amount of diversity components where the rangeland manager should attend on this scale for conservation of plant diversity.
