Patterns of distribution and plant diversity in along elevational gradient (Case study: Moghan-Sabalan rangelands)

The study of plant communities is the best way to learn about vegetation structure and distribution as well as various interactions among the plants in an ecosystem. Elevation factor plays a vital role in plant distribution that ultimately leads to specific phytogeographic regions. This study evaluated the changes in species composition, density, frequency, canopy cover and palatability of species along the elevational gradient in the sampling plots, which were conducted from 100 to 3300 meters above sea level. In each site, three 100 m transects and along each transect, 10 plots of one m² were sampled. In each plot the parameters of species composition and density, the canopy cover of each species were recorded. One-way analysis of variance and Duncan test were used to examine elevation with various life-form spectra and grouping. Regression analyses were employed to explore the inter-relationship of elevation with plant index. A total of 387 species belonging to 200 genera and 44 families were recorded from the study area. Results showed that Asteraceae family is by far the most species-rich family, followed by Poaceae and Fabaceae. The number of species was highest (168 species) at the elevation of 1200-1500 m and lowest (29 species) at 3000-3300 m. The number of plant varieties was increased with the increment of elevation up to 1500 m, whereas, the frequency of plant varieties was decreased in high elevation areas (>1500m). The diversity and species richness increased with increasing elevation and then declined while canopy cover showed a reverse trend. The species class I and II declined as the elevation increased and then increased, while class III species showed a reverse trend. The maximum species diversity at the middle elevation of disturbance is the result of inappropriate management and poor rangelands.