بررسي تغييرات درجه اهميت گونه هاي اسپند و درمنه دشتي در اطراف آبشخوار در مراتع زمستانه چاه نو دامغان

Studying variation in importance value of two species Peganum harmala and Artemisia sieberi around watering point in winter rangelands of Chahe-Nou, Damghan, Iran

watering points are from the most effective factors that influence grazing distribution in rangelands. Where other limiting factors such as slope, height and soil have no variation, forages utilization by livestock is limited by distance from watering points. In this research, the effects of livestock overgrazing on vegetation of a critical area around livestock watering point were investigated in a flat and arid rangelands in Chahe-Nou of Damghan, Iran. In ordet to determine of degraded area around watering points, the importance value of two species of Peganum harmala and Artemisia sieberi in 8 geographic directions were analysed by using ANOVA and Duncanʹs multiple range test. The association of two species of Pe.ha and Ar.si was studied using Chi-squer test. Transects of 1.5 km were laid out in 8 geographic directions around watering point and samples were taken systematically. Each 100 m of one transect was considered as block. In each block, four quadrats of 4 m2 were plotted to measure canopy cover percentage, density and frequency of both species. Results showed that importance value of Pe.ha was not significant for all transects (P>0.05) but the importance value of Ar.si was significant (P<0.05). There were negative association between the two important species of Pe.ha and Ar.si. It can be concluded that the intensity of grazing was concentrated within 500 meters around watering point which can be considered as critical zone. The results also showed negative impact of overgrazing on vegetation structure, which may indicate the necessity for a monitoring program livestock grazing and watering points in these rangelands.