Changes in Species Diversity and Soil Seed Bank under the Exclosure and Different Intensity of Livestock Grazing in Deteriorated Forests of Middle Zagros

Overgrazing, imbalance between stocking rate and range capacity, premature enterance of livestock to range and forests, are among the main factors in range and forest destruction and changes in composition, structure and species diversity. In this study, the changes in composition, structure and species diversity under different intensity of livestock Grazing: ungrazed (UG), moderate grazing (MG), and heavy grazing (HG), after one year grazing in Sarkhalaj Deteriorated Forests (Kangavar), was investigated.

Sampling was done along 100 m transects, with 90 plots (2 m2) based on Brown blanke method to record vegetation cover of species. Whereas Sarkhalaj area, are numbered as summer woody rangelands, sampling of soil seed bank was done before seed growth season. Then after field observation of area, three site were selected that in each site, ecological characteristics such as topography (slope, aspect, height), soil type and average rainfall were the same and only differed in grazing intrnsity. The distance among sites was considered as 500 m. Then these sites treated uvder heavy and moderate grazing and in one of sites, no grazing was performed (control). Also sampling from soil seed bank in the study area, was collected in two soil depth: 0-5 and 5-10 cm in each plot. The composition and amount of seed bank were determined by seeding method in greenhouse.

 The results showed that MG and HG caused change in species diversity by decreasing of cryptophytes and trophytes and increasing of hemi-cryptophytes, chaemophytes and phanerophytes in the study area. Also, diversity indices of vegetation and seed bank in HG, were very lesser compared to UG area which indicats the severe changes of species diversty due to overgrazing. The results of this study showed that, livestoch grazing could be applayed as a management tool to enrichment of phanerophytes (shrubs) in woody rangeland.The results showed that MG and HG led to change in species diversity, so that by increasing of graze intensity cryptophytes and trophytes species were decreased, wherease hemi-cryptophytes, chaemophytes and phanerophytes spesies were increased.Also, diversity indices in HG area were lesser than ungrazing area, wherese diversity indices of MG was more than HG.

 Overally, results of this study showed that annual exclosure oprations can increase the diversity indexes and when exclosure is not possible (because of rural and nomad's needs for rangeland forage and impossibility of exerting rangeland exclosure in such vasst area, MG can be a higher priority.