Effects of road age on diversity variation and species importance value (SIV) at various distances from the roadside (Case study: Western Guilan forests)

The purpose of this study was to evaluate the effect of road distance and age on roadside vegetation cover on  Nav district forest roads in the west of Guilan province.Therfore required data in 240 Systematic random plots on linear transect in two road age classes were collected. Percentages of vegetation were calculated using Brown Blanket combination scales. Then, the values ​​of richness, evenness, Shannon-Wiener, and Simpson indices were calculated for each age class of road. Relative importance index was used to determine the distribution of species abundance. The results showed that the relative importance and presence of dominant tree species in the newly constructed roads were higher than the old ones. In both age groups, the relative importance of beech (Fagus orientalis), hornbeam (Carpinus betulus) and alder (Alnus subcordata) saplings was higher than other species. Also, the relative importance of tree species decreased with increasing distance from forest road. Also at different distances of the road, beech and maple regeneration were the most frequent. The highest values of diversity and richness were observed at 0-30 m distance from the road and its value was significantly different from other distances.