A Study of the Relationship between Vegetation and Physiographic, Soil, and Geological Factors in Tanish-e Manesht Region of Ilam

This experiment was conducted in an attempt to study the vegetation and the impact of physiographic, soil, and geological factors on the distribution of plant communities in Manesht region in Ilam province. To analyze and determine the ecologic groups, 125 square sampling plots with an area of 400 square meters was collected from the region following a systematic-random design. To determine the soil factors, two soil samples (0–30 and 30-90 cm deep) were collected from each land unit and the parameters such as soil texture, pH, EC, saturated moisture, lime, organic matter content, N, P, K, bulk density, and partial density were measured. Using TWINSPAN, the vegetation of the study area was classified. Afterwards, PCA and CCA procedures were used to investigate relationship between the vegetation and the environmental factors and to determine the most effective factors. The results of PCA and CCA analyses revealed a significant relationship between the distribution of the ecologic groups and the plant species with the physiographic, soil, and geological factors. The most significant environmental factors contributing to the distribution of the ecologic groups in the region included the geologic formation and the organic and lime matters. The CCA result was entirely consistent with the PCA, but CCA shows more details about the relationship between species and the environment while PCA illustrates the relationship between the ecologic groups, the prominent species, and the environmental factors.