Effective factors on presence on Rheum ribes and preparing the predicted map of it's (Case study: Chah-torosh Rangelands of Yazd province)

The aim of this research was to study the relationships between presence of Rheum ribes and environmental factors in Chah-torosh rangelands of Yazd province. Topography، climate، geology، soil and grazing intensity were determined. Sampling method was randomized–systematic. Within each sampling unit 3-5 parallel transects with 300-500 length، each containing 30-50 quadrates (according to vegetation variations) were established. Quadrate size was determined for each vegetation type using the minimal area. Soil samples were taken from 0-30 and 30-80 cm in starting and ending points of each transect. Measured soil properties included gravel، texture، available moisture، saturation moisture، organic matter، lime، gypsum، pH، electrical conductivity and soluble ions (Na+، K+، Mg2+، Ca2+، Cl-،Co3-2، Hco3-، and Sou-2). Logistic regression and geostatistical technique was used to analyze the collected data. The results showed that the presence of Rheum ribes is mainly related to soil characteristics such as clay and organic matter. The presence of Rheum ribes has inverse relation with clay and positive relation with organic matter.