A Simulation Model for Estimating Herbage Standing Crop and Grazing Capacity in Sar Ali-Abad Summer Rangelands of Golestan Province, Iran

To find an accurate and rapid method of estimating herbage crop, Double Sampling (DS), Comparative Yield (CY), and clipping and weighing (CW) methods were applied to a summer rangeland in North-eastern Alborz Mountains, Iran. The method was called SMFY (Simulation Model of Forage Yield) to emphasize the statistical aspects of simulated model. In representative stands five 1-m2 reference plots were chosen to represent the ranges of standing crop. Using a systematic-random design, 180 1-m2 plots were ranked against the reference plots for CY, visually estimated for DS, and subsequently, all of them were Clipped and Weighed (CW). After clipping and weighing 5 reference plots with 6 replications for CY and estimating and clipping 37 plots for DS, regression lines were plotted between the estimated, ranked, and clipped plots. This study was conducted during 2011-13. There was high correlation (0.90-0.99) for DS and CY, so the estimated and ranked data were corrected based on the regression equations. There were strong linear relationships between the corrected and clipped data for the DS and CY methodswhich confirmed the suitability of both methods against the CW, so all of 180 estimated plots were corrected and were compared by ANOVA. The non-significant F for CY, DS, and CW confirmed the high efficiency of DS and CY, so based on the estimated production, grazing capacity of study area was calculated. Preferring one of these methods depends on further research in time and cost efficiency of DS and CY. Available DM of 389.75 kg/ha support 6.5 AUM per ha and for the grazing period of 4 months, each hectare of this rangeland can carry on 1.62 AU per ha. The current stocking rate of study area is about 0.82 AU per hectare which was suitable based on carrying capacity of study area.