Investigation of some environmental factors effective on Astragalus gossypinus in Zagros mountainous rangelands (case study: Hamadan Province)

Vegetation cover is one of the most important factors for sustainability of ecosystems and catchments; thus recognizing and understanding factors that affect growth and development of vegetation societies is necessary. The aim of this study is to investigate the relations between "Astragalus gossypinus" with some environmental factors (soil characteristics, slope, aspect and elevation) and identify the most important affective factors in mountainous rangelands of central Zagros. So, three elevation and slope classes and four aspect (skirt) classes have been determined in the study area. Flora and vegetation types were studied by physiognomic- floristic method in the field. The factors of vegetation were measured by transect using systematic-randomized method. Four transects (100 m) and 5 plots were used. Three soil samples (complex) in each area collected in 0-50 cm and parameters such as pH, EC, N, P, K, TNV, OC and texture were measured. Investigating of the relations between density and cover percentage of A. gossypinus (dependent variables) and soil and topographical factors (independent variables) has been done by multiple regressions. Statistical analysis of data showed that density and percentage cover of A. gossypinus have significant linear regression with soil and topographic factors. In topographic factors; southern aspect, 20%-30% slope and 2100-2300 m elevation and in soil factors; pH, K, sand and silt have most relationship and significant role to anticipate of density model. For anticipation of cover’s model, in topographic factors; southern and northern aspects, 20%-30% and 30%-50% slope and 2100-2300 m and 2300-2500m elevation and in soil factors; pH, K, sand and silt have most relationship and significant role.