Dept. of Forestry, Faculty of Natural Resources, Guilan University, P.O.Box 1144, Somehe Sara,
The depletion of forest in developing countries due to extended pastures, agricultural land, fuel wood and etc. is a serious concern. Therefore planting trees for reforestation and extended forest area is a essential assignment. Forest plantation with a basic criterion affects to understory plant diversity. This effects may make some species absent or appear. The objective of this study is to assess the plant diversity of two different plantation which established by Pinus teada and Acer insign and compare with a natural forest stand which were similar in geographic and climatic conditions. Twenty sample plots with 32 square meters were randomly selected . In each plot all herbaceous species were recorded. Richness and Evenness of plant species calculated using the biodiversity indices (Simpson index and Margalov index). The obtained results showed that the value of plant diversity was higher in natural forest, while Acer plantation had the lowest value. The Richness and Evenness value were higher in natural forest stand, while Richness and Evenness value were lower for Pinus teada and Acer insign plantation respectively.