Investigation of Flora and Geographic Distribution of Plant in Related to Climatic and Physiographic Factors in Eastern Parts of Semnan Rangelands

The main of this research is investigsting of flora and geographic distribution of plant in relatated to climatic and physiographic factors in Drayan watershed. In this study، The list of plants was provided by taxonomic studies and then by this method was determined 48 families، 92 genera and 290 species. The important families are Compositae with 37 species and Cruciferae with 14 species، are maximum and minimum respectively. About 236 species were perennial and 54 species were annual. The life form of plant species was determined by using Raunkier’s method. Life forms of plants are including: 33% hemicryptophyte، 28% therophyte، 17% chamephyte، 12% phanerophyte، 6% cryptophyte and 4% geophyte. 254 species (88%) of the area are exclusively Irano-Turanian region. Among these plants about 30% are medicinal، 49% pastural، 7% poisonous، 4% with industrial uses and 10% weed. Vegetation classification using dominant species and vegetation map of the area was conducted and 18 vegetation types were identified. To study the geographical distribution of plants use of ecological variables. The invetigated climatic variables are included precipitation، maximum temperature and mean annual temperature; evaporation and Physiographic variables are slope and elevation. The componante 1 of PCA method showed the association with precipitation and elevation and component 2 showed association with slope.