Investigation on Environmental Factors Influencing Distribution of Plant species (Case study: Damghan Region of Semnan Province)

The purpose of current study is to investigate the cause of plant species' distribution in association with environmental factors to find the most important governing factors in the relation to vegetation cover and environmental factors (soil characteristics, slope, aspect, elevation and precipitation). Working units serving as the bases of the research were established, and after preparing maps of slope, aspect, elevation, lithology and geomorphology and combining the maps, a single working map was compiled. In order to study plant cover in each unit, random-systematic sampling was conducted in 10 plots. Regarding the species studies and distribution, the area of each unit was determined based on the minimal area method. Floristic list, canopy cover and density of species were determined in each plot, and vegetation type of each working unit was listed with respect to two dominant species. Furthermore, 5 profiles were sampled within the plots to study soil characteristics in 0-50 cm depth as the effective depth of rooting. Subsequently, the texture, percent of lime, gypsum, organic matter as well as pH, EC, SAR and ESP were measured. To study the soil and vegetation cover the Principal Components Analysis (PCA) was used through PC-ORD software program. The results showed that among environmental factors, elevation, precipitation and slope as the first set of factors determine the change in the vegetation cover by 39.29% while the second set of factors, including sand percentage, loam and ESP plays contributes to the change by 20.5%. These two sets of factors altogether explain 59.79% of vegetation cover variation in Damghan region.