Vegetation change after 19 years of grazing exclosure in the central Zagros region

High grazing pressure has been considered as the main reason for degradation of Iran’s rangeland over past few decades. A key question for range management is therefore whether temporary exclusion from grazing would lead to spontaneous regeneration of the vegetation. If so, it is important to know how long this regeneration will take and whether the regeneration pathway is the same in all sites. A long-term exclosure experiment was established to assess effects of grazing exclusion on rangeland recovery in arid and semi-arid rangelands in Iran. The experiment was carried out in 17 rangeland sites in central Zagros region. At each site, an exclosure and inside each exclosure seven permanent plots (1.5 × 2 m) were established in 1983. After 19 years (2002), vegetation, including cover and density for each species, total vegetation cover, litter cover as well as annual forage production, were measured in these seven permanent plots and also in 10 randomly located plots (1.5 × 2 m) outside each exclosure. The comparison between inside and outside exclosures showed that after 19 years, total vegetation cover, litter cover, annual forage production, the number as well as the relative abundance of grasses and legumes, and the percentage of palatable plants were significantly increased inside exclosures. The overall similarity between different sites inside exclosures was also increased. In conclusion, 19 years grazing exclusion has changed the species composition of the vegetation in most sites. This study confirms convergence of vegetation development during the secondary succession.