The evaluation of utilization of key species is cornerstone of decision-making in rangeland management. Measuring utilization is essential for regulating grazing intensity, grazing pressure and distribution of animals. utilization of two key grass species of Dactylis glomerata and Bromus tomentosus, as two important rangeland species is determined using height-weight relationship. The research is done in two vegetative periods of prior to flowering and flowering stages in two region of grazing land and exclosure by 32 transects of 100-meter length. To do so, the height of species was measured and cut at 1-cm above soil surface and weighted freshly. The samples are clumped and moved to the laboratory and oven dried at 65°c after separating litter divisions Then, the whole individual plants were weighted and cut in 5-cm intervals and each part was re-weighted and recorded separately for each species. Height-weight relationships were analyzed by different regression models in SPSS v.18 software.
Result shows that sigmoid model significantly illustrate the height-weight relationship of both species of Dactylis glomerata and Bromus tomentosus with R2=0.994 and 0.997 at prior to flowering stage in the exclouser respectively. Similarly, sigmoid model also elucidate the height-weight relationship of both species of Dactylis glomerata and Bromus tomentosus with R2=0.975 and 0.998 at the flowering stage in the exclouser, respectively. The sigmoid model also best fitted for depicting height-weight relationship of both species at prior to flowering stage in grazing land for both species with R2=0.996, too.