Investigation Plant Species Diversity and Physiographical Factors in Mountain Forest in North of Iran

Species diversity is one of the most important specifications of biological societies. Diversity of organisms, measurement of variety and examination of those hypotheses that are about reasons of diversity are such as affairs that have been desired by the ecologists for a long time. In this research, diversity of plant species in forest region, numbers of 60 sample plots in 256.00 square meters have been considered in random - systematic inventory was considered. In each sample plot, four micro-plots in 2.25 square meters in order to study on herbal cover, were executed that totally 240 micro-plots were considered. At each plot six diversity indices in relation to physiographic factors (slope, geographical aspect and altitude from the sea level) were studied. The results indicate that species diversity is more in the northern direction and also species diversity in slops less than 30% has the most amounts. Factor of altitude from the sea level did not have meaningful relation with species diversity. Through study on correlation of the numbers of species in sample plots with indices and also process and role of indices in different processors of analysis, Simpson's reciprocal index was suggested as suitable index in this type of studies.