Beta diversity of plant community and soil mesofauna along an elevational gradient in a mountainous semi-arid oak forest

Community composition heterogeneity and its changes along environmental gradients are important aspects of landscape management and conservation. However, variations among different trophic levels are still poorly understood. This study aimed to evaluate the variability of beta diversity and its components (spatial turnover and nestedness) along an elevational gradient in two dominant exposures (north and south) for plants and mesofauna in a semi-arid oak forest in western Iran. Vegetation sampling was conducted in randomly distributed macro-plots (100 × 100 m2) in which the abundance of herbaceous and woody species was recorded using five plots of 2 × 2 m2 and three plots of 20 × 20 m2, respectively. Soil and litter samples were separately collected in each 20 × 20 m2 plot with a cylindrical soil extractor. The beta diversity of plant and mesofauna samples was additively separated into spatial turnover and nestedness, and these variables were regressed against elevation for each group. Compared to mesofauna, plant beta diversity and its components were more affected by topographic variables. Spatial turnover was the main driving mechanism of beta diversity in both mesofauna groups (soil vs. litter). In the case of plants, however, spatial turnover was also related to plant functional groups and topographic characteristics. Compared to mesofauna, plant diversity was more closely related to elevation although this relationship differed between functional groups. These results suggest that herbs are more sensitive to environmental gradients than mesofauna and can therefore be considered as sensitive indicators of environmental variations.