The effect of physiographic factors on plant biodiversity of natural desert ecosystems in Kakhk Gonabad

Determination of factors affecting on species distribution and diversity¡ especially in desert areas is the most important factor in rangeland ecosystems management for encountering biological stress. In order to evaluate the effect of physiographic factors on plant biodiversity in natural ecosystems of Kakhk Gonabad¡ this research was conducted in spring 2014. First¡ by overlaying four maps of slope¡ aspect¡ and elevation and geological formations working unit maps were prepared. Then¡ 4 homogeneous types were determined based on the structure¡ distribution¡ and presence of dominant species and sampling was done in each vegetation type in homogenous working units. In each type 35 plots were systematic-randomly selected and based on the minimum area method¡ 4 m2 plots were used to estimate vegetation. Vegetation sampling was carried out in all plots. Plants were recorded in each plot and canopy coverage and physiographic properties such as slope¡ aspect and elevation were measured and diversity in different geological formations was determined. The study of plant biodiversity was performed by evaluating the density of different plant species per plot and using diversity indices of Shannon-Wiener and Simpson¡ richness index of Margalef and evenness index of Smith-Wilson in Ecological Methodology software. The results showed that altitude had significant effect on diversity¡ richness and evenness of plant species; at the elevation of 1700-1900 m¡ Simpson and Shannon Weiner had the highest value respectively; while¡ evenness of species were higher in altitude between 1900-2100 m. In addition¡ slope had significantly affected the diversity and richness; the highest diversity and species richness were allocated to the 0-20% slope. Northern aspect had significant affects on the biodiversity indices.