The Effect of Single Selection Method on Tree Species Diversity in the Northern Forests of Iran (Case Study: Asalem-Nav, Guilan Province)

Little is known and studied about the effects of single selection method on the biodiversity of Hyrcanian forests. In this research after ten years, the effects of single selection method on tree species diversity were studied in 2 parcels with 105 ha of Asalem-Nav forest area. Systematic sampling design at the begining (2000) and the end (2010) of forest management plan with 100m grid dimension and 1000m2 circular shaped plots were used for data collection. Species diversity indexes in each plot were calculated and those averages in two sampling were compared through ANOVA and t- test. The results showed that species diversity index increased slightly in the four layers of seedling, large sidling, sapling and tree, but this amount of increase was not statistically significant. The increase of species diversity index in seedling and large seedling layers were due to the increase of richness index of those layers, but in sapling and tree layers were created due increase of evenness index of those layers. Index of species richness was decreased in tree layer. Therefore, SIV (species importance value) of Fagus orientalis and Carpinus betulus decreased, but SIV of Acer velutinum, Acer cappadocicum and Alnus subcordata increased. Cosequently, we can conclude from the result obtained that selection method is suitable for these stands, but tree species diversity can be conserved in the future along with timber production when enough attention is paid to the index of tree richness and tree SIV at the time of tree marking.