Investigation of Relationship and Roles of some Topographic Factors Effecting Astragulus Vegetation in Central Zagros

This study aimed to investigate of relationships between Astragulus and topographic elements such as aspects, slope and elevation classes in central Zagros. For this purpose, the study area was divided to three elevation classes and three classes of slopes and defined four aspects in it. Vegetation types were studied by physiognomic- floristic method in the field. The factors of vegetation (canopy cover and density of Astragulus) were measured by transect with systematic-randomized method. Data were analyzed through analysis of variance one way (ANOVA) and homogeneity Duncan test. Statistical analysis indicated that maximum and minimum canopy cover percentage of Astragulus respectively was related to eastern and western aspects. Maximum and minimum density of Astragulus respectively related to northern and southern aspects. The elevation class of 2300-2500m had the highest canopy cover and density of "A. parrowianus" and the minimum of these factors occurred in elevation class of 2500m< and slope class of 50-60%. We found that grazing intensity (excessive), intentional and prescribed fire, change of rangeland use to agriculture in low elevations, low soil depth, intensive winds all caused to canopy cover decrease and density of A. parrowianus.