تأثیر سه شدت چرا بر عملکرد اندام‌های هوایی و زیرزمینی گونه‌های Festuca ovina و Alopecurus textilis در منطقه شابیل (شمال سبلان)

The effects of different grazing intensities on the above and underground biomass of twospecies Festucaovina L. and AlopecurustextilisBoiss. in the north Sabalan rangelands (in Shabil) were investigated. Sampling on the light, medium and heavy grazing intensities in the flowering stage (the second half of June 2013) were performed. Initially, from a 90-meter transects perpendicular to the slope at each site 10 plots each one square-meter were sampled to determine the total production and the share of each species in the production. Afterwards in each site, three 50 meter transects other than previous ones were randomly chosen to investigate the effects of grazing and the reaction of different aerial and underground parts to grazing. In each transect, 10 points were randomly selected, and on each point the nearest plant species was selected. After weighing, the weight ratio of the aerial and underground biomass was determined. Correlation and regression analyses were carried out to determine the relationship between parameters of root length and aerial height and root weight and aerial biomass which indicated significant relationship between these parameters (p<0.01). Moreover, for the comparison of mean length and weight of root and shoot organs under different grazing intensities ANOVA and Tukey’s test were used. The results showed significant differences between different grazing intensities (P<0.01). The results of ANOVA and Tukey’s test showed that the length of roots in light, medium, and heavy grazing were significantly different (P<0.01). The highest length in the twospecies was observed in light grazing and the lowest in the heavy grazing intensity. The weight of root had also significant differences in light, medium, and heavy grazing intensities. Overall, for each species the highest weight of root was in light and the lowest in the heavy grazing intensities. According to the results, decreasing aerial biomass and underground parts of plants were directly related to the intensity of grazing and harvesting volume of aerial organ and as such, the root development in areas of heavy grazing is severely limited.