Effect of Ailanthus altissima stand on herbaceous species diversity (Talesh, Guilan)

Reforestation with native and exotic species has a significant effect on the diversity of plant species. This study was done to investigate the effect of Ailanthus stand (Ailanthus altissima) on herbaceous layer diversity in Talesh, Guilan province. Two sites viz. Ailanthus stand and natural forest were selected and 20 400 m2 sample plots were established in each stand as a systematic-random grid. Whittaker's nested plot sampling and minimal area method were used to determine the optimum plot size of the understory. Therefore, micro-plots of the size 16 m2 were established in the center of each plot and cover percentage of each species was estimated according to Braun-Blanquet approach. In general, 21 species of 15 families were recorded in the study area. Results indicated that the average of litter depth, the number of trees per hectare, the average of canopy cover percentage of trees and the average of herbaceous cover were higher in the natural forest. The species diversity and richness indices were higher in the natural forest than those in Ailanthus stand, while evenness index was higher in Ailanthus stand. Studying the abundance distribution models showed that both areas followed a lognormal distribution. Ailanthus species has reduced the diversity and richness indices. Therefore, in order to enhance the plant diversity in these areas, a combination of trees in plantation programs must be used instead of pure plant species.