In this study the effects of climate change, including three variables i.e temperature, carbon dioxide concentration and pattern of soil moisture on physiological characteristics of the two important forage plants species in pastures of West Isfahan province namely Bromus tomentellus pasture and Agropyron trichophorum were studied. The results showed that increasing carbon dioxide concentration from 380 to 700 µmol mol-1, caused an increase of 36/5, 27/1, 54/9, 14, 23/8, 28, 22/01, 14 and 23/4 percent in greenness index (SPAD), chlorophyll a, chlorophyll b, leaf area, leaf soluble protein, the concentration of soluble sugars, The concentration of soluble sugars underground parts, aerial percent of the total dry weight, shoot dry weight, respectively. However, stomatal conductance and rhizomes percent of the total dry weight decreased by 33/1 and 8 percent respectively. Increasing temperature, reduced stomatal conductance, chlorophyll a, chlorophyll b, leaf area, shoot percent of the total dry weight, shoot dry weight by, 13/5%, 44/7%, 44/2%, 14/9%, 15/8% and 23/5% respectively. However the concentration of soluble protein, underground soluble sugar concentration and parts of the rhizome of total dry weight increased by 36/2%, 12/4% and 20/7% respectively. The effect of soil water deficit, reduced stomatal conductance, greenness index (SPAD value), chlorophyll a, chlorophyll b, carotenoid concentration, leaf area, shoot percent of the total dry weight, shoot dry weight by 41%, 32/9%, 56/7%, 54/8%, 47%, 35/6%, 22/1% and 36/9% respectively. However The concentration of soluble sugars, soluble sugars concentration of underground organs, the root proportion of total dry weight, rhizomes proportion of total dry weight and underground dry weight increased by 6/16%, 11/4%, 14/8%, 9/71% and 35/2% respectively. Regardless of the pattern of humidity and temperature, increase of carbon dioxide concentration of species Agropyron trichophorum and Bromus tomentellus increased average shoot dry weight, respectively by 14/5 and 38/1 percent. Therefore if all three of analyzed climatic parameters change with the conditions predicted in the A2 scenario for the year 2080, Bromus tomentellus species,will have higher positive reaction to the increase of CO 2 in terms of rising temperature and decrease in humidity levels. However, by changing all three elements of carbon dioxide, temperature and humidity, Agropyron trichophorum species will be a higher performance than any Bromus tomentellus. Keywords : Environmental factors, climate change, Agropyron trichophorum, Bromus tomentellus, rangeland ecosystems, Isfahan