Investigation of grazing tolerance of species (Agropyron intermedium، Oryzopsis holciformis and Thymus fedtschenkoi Ronniger.) in Firoozkooh Rangelands

This research was aimed to determine the best harvesting intensity for key and indicator species including Agropyron intermedium, Oryzopsis holciform, and Thymus fedtschenkoi in the cold semi steppe rangelands of Firoozkooh. Treatments consisted of different harvesting intensities of 25%, 50%, 75%, and control. In the first year, an area of one hectare was selected and fenced. From each of the above species, 40 average individuals were selected and each of the above treatments was applied on 10 individuals. The study individuals were distinguished by numbered signs and the harvesting was done manually by clipper. The data were analyzed in a split plot design in time and the means were compared using Duncan test. The results showed that the highest (24.59, 10.57, and 10.52 g) and the lowest (20.17, 9.91, and 5.78 g) yield were obtained at 25% and 75% harvesting intensities. According to the results of means comparison in different, the reduction of forage yield was affected by the harvesting intensity. The lowest (15.61, 8.59, 9.14 g) and highest (24.6, 10.8, 12.7 g) forage yield were recorded for the low-rain year (2008) and the wet year (2009), respectively. Therefore, a harvesting intensity of 25-50% could be recommended for the study species.