شهرام عابدی

Study of exclosure effects on vegetation changes under grazing and no grazing conditions in rangelands is of particular importance in range improvement programs. The reseach was performed in Semi- Steppe area of Bilehvar, Khoy from 1998 to 2006. The vegetation cover was measured every year inside fixed plots along the transacts. The results indicated the increase of total canopy cover inside the exclosure occurred during 9 years of the study, where the highest increase rates were observed with perennial cereals (>3.5 times), and with perennial broad-leaf forbs (>2.5 times). Outside the exclosure, the total canopy cover approximately remained unchanged and vegetative forms showed less changes. Inside the exclosure, favorable species appeared with a vegetation composition of about 19%. The proportion of increasers in the vegetation composition increased to more than double, however non-favorable species decreased to half. Outside the exclosure, desirable species were rare and the proportion of increasres increased to 28%. Average vegetation cover of annual plants inside the exclosure was higher than that of the outside, while average vegetation cover of the forbs compared to annual cereals were more predominant inside and outside the exclosure. During the study (9 years) in Bilehvar, a significant correlation was found between precipitation changes and canopy cover of the most species.