Selection of the Most Important Effective Environmental Factors on the Distribution of Dominant Plant Species for Rangelands Improvement and Rehabilitation Programs, (Sorkhdeh Rangelands, Semnan Province)

There were relationships and interactions between plant species and environmental factors. Because there are many effecting environmental factors in natural ecosystems such as rangeland, it is necessary to determine the most important of them to save on cost and time in the management and rehabilitation programs.  To achieve these relationships, there are several methods such as statistical methods including regression and ordination to use. The object of this research is to use logistical regression in the dry Sorkhdeh Rangelands in the Semnan provinces for determination most important soil, topography and climate factors.

The area was divided into 23 homogenous units based on slop, aspect, height and geology, and 10 plots 1m2 were established in each unit for the sampling of vegetation. 6 plant species were recognized as dominant in the study area. 3 soil samples were taken at depths of 0-15 cm in each unit, with a total of 69. Overall, 16 environmental factors were measured, including 3 climatic (mean annual temperature, mean annual precipitation and men annual humidity), 3 topographic (slop, aspect and height) and 10 edaphic (carbon, nitrogen, calcium, phosphorus, potassium, CaCo3, pH, EC, percentage of sand, silt and clay) factors.

The results showed that the vegetation distribution is mainly related to soil characteristics such as soil texture, Caco3, N, EC, and topographic factors such as aspect, and slop. The presence of Salsola dendroides, had a relationship with EC and pH and Hypocylix kerneri had most effectives from sand percent. Salsola arbusculiformis had a direct relationship with Caco3 and clay percent. and Artemisia aucheri with C, mmps, Mmts. Salicornia herbaceae had direct relationships with pH, Clay, K, and Halocnemum strobilaceum with EC. All of the models were significant at p<0.01 level.

As the results of the present research showed, this method was able to extract the most important factors and their effectiveness. Among the advantages of this method, can be referred the possibility of using data on the presence or absence of plant species without using other vegetation information, such as the percentage of plant cover, density and frequency, which are affected by the sampling method, plot size and fluctuation of rainfalls.