Investigating the relationship between species diversity and topographic factors in rangelands of Delfan County- Lorestan province

One of the goals of natural resource management is to preserve biodiversity in natural ecosystems. In this research, the effect of topographical factors on species diversity in the elevation gradient of Grain mountains rangeland in Delfan County in 2022 was investigated. In this elevation gradient, five habitats were selected. Vegetation typing was done by the physiognomic method and in the Key area of ​​each plant type, vegetation sampling was done by a random-systematic method. The sampling plot area was determined by the minimum area method (one to four square meters) and the number of plots was determined by statistical method for each habitat, 30 plots. Three transects with a length of 100 m were deployed in each habitat and 10 plots were sampled along each transect (30 plots per habitat). Species were collected from the surface of the plots, identified and their vegetative form was determined. The Biodiversity of plant species was calculated using dominance, Shannon-Wiener and Simpson diversity indices, Margalf and Mannhing richness index and homogeneity index Hill using PAST software. A One-way analysis of variance was used to compare the differences between sites and the Duncan test was used to compare the means. In order to determine the most important factors affecting species diversity changes, principal component analysis was used. The results showed that changes in height, slope and direction had a significant effect on the indices of diversity, richness, homogeneity and dominance at the level of all plants. At the total level of plants, the highest values ​​of richness and diversity indices were observed at an altitude of more than 2600 meters and dominance at an altitude of 1850 meters. In low slope (0-15%) the dominance index had the highest value and the indices of diversity, richness and uniformity in slopes higher than 30% had higher values. Most indices in northern, northwestern and western geographical directions had higher values ​​than in other directions and the difference was significant (P <0.01). The results of the principal component analysis showed that high altitude and slope and north, west and northwest directions have the most impact on species diversity in the study area. In general, it can be concluded that due to the number of livestock exceeding the grazing capacity and human activities in the lower elevations of the studied area, species diversity and richness have decreased.