Impacts of simulated grazing on some vegetative and reproductive characteristics of Stipa barbata in Majidabad rangelands of Kurdistan

For assessing clipping (simulated grazing) effects on Stipa barbata as an important species, a half hectare exclosure field was established before 2007 growing season in Majidabad paddock. Inside the exclosure area, 40 plants were selected of which 10 replications were allocated to each specific treatment of ocular-estimated hand clipping of 25, 50 and 75 percent of annual growth. Ten replications were assigned as control (unclipped) plants. Clippings were done monthly during the three months of current grazing season. Monthly-clipped plant materials were dried in free air to calculate the accurate clipping intensity. In addition, the residues of all plants (also controls) were clipped and dried simultaneously at the end of growth season. The study was done for four years. A split plot in time was used as the statistical design and analysis. The results showed that the main effect of year and different clipping intensities and interactions effect of different clipping intensity and years were significant on forage production but no significant difference was found on final height and number of reproductive branches. Most and least amount of production were related to the years of 2007 and 2008 with 508 and 167 mm of rainfall, respectively and 75% treatment (severe clipping). As the overall conclusion, regarding the environmental and management variations of this species, it is adapted with light clipping (25%) and maximum allowable use of one third of the annual yield growth.