Investigation on some environmental factors influencing distribution of plant species (Case study: Ghara Aghach watershed, Semirom, Iran)

The purpose of current study is to investigate the cause of plant types distribution in association with some of environmental factors to find the most important governing factors in the relation to vegetation cover and environmental factors (soil characteristics، slope، aspect، elevation، lithology، geomorphology faces and precipitation). In order to study plant cover 17 plant types were determined in study area and random-systematic sampling in each plant type was conducted in 10 plots. Regarding the species type and distribution، the area of each plot was determined based on the minimal area method. Floristic list and canopy cover of species were determined in each plot، and vegetation type of the area 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، organic matter، pH and EC were measured. Statistical analysis of soil and vegetation cover was done using the Principal Components Analysis (PCA) through PC-ORD4 software program. The results showed that among environmental factors، slope، aspect، organic matter، surface stone، loam and sand percentage as the first set of factors determine the change in the vegetation cover by 54. 06% while the second set of factors، including EC and elevation plays contributes to the change by 21. 17%. These two sets of factors altogether explain 75. 23% of vegetation cover variation in Semirom region.