Species diversity and plant groups changes under different grazing intensities in semi-steppe rangelands of Central Zagros

For sustainable management of livestock grazing in rangeland ecosystems, comprehensive understanding of vegetation dynamics and their response to grazing intensities is necessary. This will help for   identifying causes of changes in composition and vegetation communities. In this study, life span, vegetative form, life form, plant families and palatability classes as functional groups, and diversity, richness and evenness indices were used in investigation of vegetation response to different grazing intensities. The study was conducted under four grazing intensities (non, light, medium and heavy) in semi-steppe rangeland of Karsank and Bardeh, Chaharmahal & Bakhtiari province, Iran. Sampling was made at representative and homogeneous areas of each grazing intensity by random-systematic method and canopy cover of plant species were measured in 240 plots. The results showed that increasing grazing intensity, species diversity and richness according to margalef indices are decreased.  Under the same condition menhinick and evenness indices showed higher number for species diversity and richness. Among the studied plant families, by increasing grazing intensity the canopy cover of Chenopodiaceae and Euphorbiaceae increased and the canopy cover of Poaceae, Fabaceae, Asteraceae and Apiaceae decreased. Except perennials, hemicryptophytes and perennial grass, showed a significant reduction from the reference area to the critical one. Comparison of most functional groups also indicated reduction in their canopy cover percentage at higher grazing intensity. Reduction of plants of class I and II of palatability is seen from non to heavily grazed area.