The Assessment of Plant Species Importance Value (SIV) in Beech (Fagus orientalis) Forests of Iran

ABSTRACT: The aim of this research was to determine plant Species Importance Value (SIV) in the Fagetum orientalis, Nav district of Asalem, Guilan province. The sampling procedure was performed according to the transect method. Seventy three plots were sampled and tree, shrub and herb species were identified. Their frequency and coverage percentage were measured within each sampling plot. Species Importance Value (SIV) was calculated in the tree, shrub and herbaceous layers. The diagrams were drowning based on log SIV. The results indicated that the mean richness of tree, shrub and herb species in Nav were 11, 12 and 79, respectively. The highest and lowest value of the SIV tree species layer belong to Fagus orientalis (142.88%) and Sorbus torminalis (2.84%), in the shrub species layer Ilex spinigera (86.23%) and Prunusdivaricata (1.40%) and in the herbaceous layer Asperulaodorata (83.06%) and Physalisalkekengi, Capsella bursa – pastoris, Carpesiumabrotanoides, Humuluslupulus, Petasileshybridus and Physalisalkekengi (1.38%), respectively. Diagrams of species frequency followed a lognormal pattern, which shows that the majority of species are of moderate presence in the community and a few number of them are more frequent or rare.