Determination of Allowable Use and Grazing Tolerance of Picris strigosa (Case Study: Blooman rangelands, Lorestan Province, Iran)

Picris strigosa is a valuable forage species in mountainous rangelands of Lorestan province, Iran, which produces suitable forage for sheep grazing. The aim of this study was to determine the allowable use and grazing tolerance of this species. For this purpose, 50 individuals of P. strigosa were selected in its typical habitat and marked for monitoring after applying four levels of harvesting intensities including control (0%), 25, 50, and 75% of the annual production during 2007–2011. Treatments were investigated by clipping and weighing method every month from May to July in vegetation period. The results showed a significant difference in terms of forage production between treatments (P≤0.01). The highest and lowest forage production with average values of 42.45g and 15.23 g per plant were obtained in 0% harvesting rate (control) and 75% intensity rate, respectively. In other words, harvesting higher than 50% coupled with early grazing (April and May, in accordance with the local pattern and research method of this article) weakens the individuals. Continuation of this process also increases the mortality of the individuals (death of 30% of the stands at a harvest intensity rate of 75%). Due to the sensitivity of the species to early grazing, it was recommended that for such a dominant species, livestock should enter the pasture in early June. Maximum forage production in control and the fast reduction in forage production of 75% treatment emphasize that overgrazing of this species would completely eliminate it from the field. It was concluded that P. strigosa is sensitive to grazing and its sensitivity should be considered in rangeland management plans.