Journal of Rangeland Science (JRS) Plant Diversity and Richness in Relation to Environmental Gradient in Zagros Ecosystems, West of Iran Volume 5 (2015) Issue 4, October 2015 2024 01 30 Plant Diversity and Richness in Relation to Environmental Gradient in Zagros Ecosystems, West of Iran EN Javad Mirzaei Assistant Professor, Department of Forest Science, Faculty of Agriculture, Ilam University, Ilam, Iran Arash Karami Ph.D. Student, Department of Forest Science, Faculty of Agriculture, Ilam University, Ilam, Iran Journal Article 2024 01 30 Plant diversityis essential to maintain the health of planet's ecosystems. Conservation of biodiversity is necessary for the ecological stability and productivity in natural ecosystems. The aim of this research was to study the biodiversity and richness of plant species (including trees, shrubs and grasses) related to the environmental factors (soil and physiography) in the forests of Zagros, west of Iran. This study was conducted in Manesht-Ghalarang protected area in the north of Ilam province, Iran. For this purpose, some plots with a systematic distribution were selected and vegetation (trees and herbaceous), soil factors (organic matter, pH, electrical conductivity, limestone, nitrogen, potassium, phosphorus, bulk density and soil texture) and physiographic ones (slope, aspect and elevation from sea level) were measured. Results showed that the diversity of ground vegetation had a negative correlation with sand percent and it was decreased by the increased slope, elevation, EC percent and silt percent in the southern aspect. In the northern aspects, richness and diversity of ground vegetation were decreased with the increased elevation from sea level. While the tree species diversity was increased by increasing the elevation. In western aspects, the biodiversity of herbaceous species increased as CaCo3 and organic matter were increased and salinity and elevation from sea level decreased. Also, the diversity of tree species in these aspects had positive reactions to potassium percent in soil.