Effect of topographic on species richness and diversity in desert and arid rangelands (Case study: Tang_e Laybid rangelands of Yazd)

Environmental gradients and land deformation cause gradual changes in non-living factors that affect the density andEnvironmental gradients and land deformation cause gradual changes in non-living factors that affect the density and distribution of species and are important for the spatial distribution of plant diversity. Understanding the ecological processes associated with altitude gradients leads to potential climatic changes in communities. To study the diversity and species richness in the rangeland, two eastern and western slopes were selected in three altitudes of 2000-2400, 2400-2800 and 2800-3200 meters above sea level. Sampling be performed Systematic random. Thus, in each altitude class, three 100-meter transects were placed perpendicular to the slope at a distance of 100 meters from each other, and on each transect, 10 plots of two square meters and in total 180 plots (2 square meters) were located and measured in the area. Then, important ecological indicators such as richness, diversity and uniformity were calculated using PAST software. Statistical analysis of these indicators showed that the most diversity is related to the altitude class of 2400-2800 and 2800-3200 meters and the least of it is related to the altitude class of 2000-2400 meters. Diversity in the east and west directions was not significantly different. Altitude class 2000-2400 meters with east direction has the highest uniformity and the lowest richness. In relation to richness, in the upper two classes of altitude (2400-2800 and 2800-3200 meters) there was the highest amount of richness and the lowest amount of richness was at lower altitudes. However, richness is larger on the western slope than on the eastern slope. The lowest uniformity was observed in the altitude class of 2400-2800 meters and the eastern and western slopes had the same uniformity. In general, with increasing altitude above sea level, diversity and richness have increased in the western geographical direction. Because more than seventy percent of the frequency of precipitation is in of the western slope and at an altitude above 2800 meters due to the cold weather, the amount of richness has decreased.