Effects of various grazing intensities on vegetation diversity and composition in semi- steppe rangelands (Case study: Alavigeh- Isfahan)

Considering the role and importance of grazing on vegetation structural changes, thisstudy aimed to assess the effects of various grazing intensities on vegetation parameters in semi-steppe rangelands of Alavigeh, Isfahan. Three rangeland locations with relatively homogeneous ecological conditions and various long-term grazing intensities (light, moderate and heavy) were selected. Four perpendicular transects with 100 meters length (two parallel transects and tow transects perpendicular to the general slope of the area) were established in each site and vegetation parameters including vegetation cover, density and palatability class of the species were recorded in 10 plots. The Margalef richness index and Shannon-Vainer diversity and evenness indices of the plots were calculated. A one way ANOVA was used to compare the vegetation parameters in sites with various long term grazing intensities. According to the results, the sites with low and moderate grazing intensities had higher plant density and vegetation cover compared with site grazed heavily and these vegetation indices varied significantly between the sites (P< 0.05). The species composition of the light and moderate grazing areas mainly included class II species with 72% and 54%, respectively. The heavily grazed site was dominated by the species with low grazing palatability (69%). The plant diversity, richness and evenness indices of the sites with low and moderate grazing intensities varied significantly (p < 0.05). The log normal was the best fitted parametric model among species abundance models for the low and moderate grazed sites, indicating a stable vegetation community. Log series were fitted to diversity data in the heavy grazed site, indicating an unstable vegetation community. RDA analysis revealed that there was a distinct grazing gradient and three vegetation zones could be clearly separated with various vegetation compositions. Although vegetation condition is appropriate in the sites with low grazing intensity, also the vegetation regeneration can benefit from moderate grazing intensity. Biological considerations are required in the management of rangeland ecosystems in arid and semi-arid ecosystems due to the fragile nature of these ecosystems.