Effect of Soil Properties on Plant Diversity of Ecological Groups in Reserved Forest of Northern Khorasan

In order to investigate the influence of soil factors on plant diversity and ecological groups in the Northern Khorasan Province، 220 hectares of Joezak-Darkesh forest was studied. At first، 55 sample plots 20 m x 20 m were selected for vegetation determination. Then، 18 samples from superficial layer of soil (depths of 0-10، 10-20 and 20-30 cm) were taken and electric conductivity، pH، organic matter (OC)، total nitrogen، available phosphorus، soil texture، K and C: N ratio measured. The first ecological species groups using two-way analysis method of TWINSPAN was conducted and the study area to five different ecological units Cotoneaster integeryma (A)، Fraxinus excelsior (B)، Prunus divaricata (C)، Carpinus betulus (D) and Acer laetum (E) was divided. Analysis of ecological species groups showed that different groups had significant difference (p <0. 05) on Simpson diversity. Duncan’s test revealed that the highest species diversity allocated to E، B and D ecological groups، respectively. This is while that، in terms of other biodiversity indices، no significant differences was detected among the ecological. Pearson regression Analysis displayed that increased of pH in 3rd depth of soil had negative effect on the Simpson diversity index and Margalef species richness. The amount of OC and K in first soil depth had positive effect on the Simpson diversity. Other soil characteristics did not affect the diversity indices. From this research it can be deduced that among the affecting factors، OC and K of first soil depth separated five-fold ecological groups in the investigated site.