study on vegetation changes of natural ranges in khoybilehvar semi-steppic area of west azarbaijan province

the study of the exclosure effects on the vegetation changes undergrazing and non-grazing conditions in the rangeland areas has particularimportance in the rangeland improvement and revivification projects. theresearch was accomplished in semi-steppe khoybilehvar area, from 1999 to2005. vegetation cover was annually measured within fixed plots during transact.the results showed that during nine years of research, on khoybilehvarexclosure, the total canopy cover has increased inside the exclosure, and thehighest increase was observed in the perennial grasses (more than 3.5) andperennial forbs (more than 2.5). outside the exclosure, the total vegetation coverwas almost constant and changes were less in vegetation cover types. within theexclosure, some desirable species appeared consisting almost 19% of vegetationcomposition. medium species proportion in the plant composition increased tomore than two times and undesirable species decreased by half. whereas, outsidethe exclosure, scarce desirable species and medium species of vegetation ratiohas increased a little. the vegetation average of annual species during the studywithin exclosure is more than outside and the vegetation average of forbs insideand outside the exclosure is more than annual grasses. nine year research inbilehvar exclosure showed that the correlation between precipitation changes andvegetation cover was significant in the most species.