Aridland ecosystems are brittele and sensitive to climate change. Fluctions in temperature and rainfall variables influence rangeland ecosystems and may result to degradation. Drought condition is more likely in these ecosystems. Drought condition occure when the rainfall decrease and temperature increase considerably in compare with annual mean conditions. The frequent drought condition, mismanagement and over utilization of resources result to decrease vegetation and animal production, hence the range mangers income decline considerably. This study aimed to investigate the effects of precipitation and temperature on vegetation characteristics in Stepp and semi-Stepp rangelands of Isfahan province. The vegetation cover percentage of plant species and their densities were recorded in 5 Steppe site and 5 semi-Steppe rangelands over a 5 and 10 year periods respectively. The climate data (97 varibales) from 6 synoptic and climatology stations were collected in these time frames. Analytical packages such as , CANOCO and PATN were used to analyse the data. Ordination and clustering techniques were used to explore the effects of climate varibales on vegetation characterisitics in the study areas. Principal component analysis revealed that the annual specieas in both Steppe and semi-Steppe sites were mainly responding to spring and April precipitation. According to the results, the perennial cover percentages and frequencies were mainly influcened by total precipitation of October to September, October to December, September to December, average daily and mean absolute maximum temperature in March. Annual precipitation, autumn rainfall and total precipitation of October to March, October to April and October to May were recognized as the main climate varibales influencing vegetation cover percentage and range plant composition in the study areas. Identification of these climate varibales is important in selecting appropriate time and years for various reclamation practices in rangeland ecosystms. Key Words : Semi-Steppe, Steppe, rangeland, vegetation, plant composition, life form, climate variables, rainfall, temperature.
