PLANT ALPHA AND BETA DIVERSITY IN RELATION TO SPATIAL DISTRIBUTION PATTERNS IN DIFFERENT PLANT COMMUNITY TYPES

While beta-diversity is shaped by spatial turnover and nestedness, research on the effects of spatial patterns of plants on these components of beta-diversity is limited. Therefore, to determine how spatial pattern in different vegetation types may be related to plant alpha- and beta-diversity as well as turnover and nestedness components of beta-diversity, we assessed plant spatial patterns in three communities dominated by shrubs, woody and trees species in the semi-arid regions of central parts of Zagros mountain, Iran. In order to determine the spatial patterns of dominant plant, the Morisita index was used. Additive partitioning diversity was used to partitioning the total diversity (gamma-diversity) into alpha-and beta-diversity and partitioning beta diversity into spatial turnover and nestedness. The observed Morisita indices indicated that dominant species in forest and shrubland were aggregated (I-d = 1.445; I-d = 1.258, respectively) while, in woodland regular patterns observed (I-d = 0.94). The positive and negative effects of aggregated patterns were related to increase and decrease of diversity within and among samples, respectively, that reflected the role of disturbances filters on vegetation heterogeneity. Partitioning beta-diversity into its components revealed that spatial turnover was the main contributor to beta-diversity that revealed the overall patterns of multiple-sites dissimilarity of our plant communities were driven by the spatial turnover (species replacement) component and not by the nestedness component. We demonstrated that disturbance types affected the importance and interactions within plants in these communities, and caused different spatial patterns of the plant taxa resulted in variation on diversity components and turnover.