Shade trees effects on some forest road pavement destruction indexes

This study explored the effect of tree shadings on a number of destruction indices for forest road pavement. Therefore, selective sampling was conducted within three various elevation classes in the Chafroud watershed in the west of the Guilan Province. Pavement distress indices of improper cross section, inadequate roadside drainage, corrugations, potholes and ruts dimensions, and loose aggregate were measured. By surveying the road, the plots with a canopy cover > 50 % and a paired plot beside each plot on the road were selected for measurements. Based on mentioned indexes, 12 distress variables were measured and compared among plots under the shadow of the trees and opened plots in three classes of traffic level. Results of analyses in low elevations showed that distresses of an improper cross section, number and area of potholes of plots with canopy cover > 50% were significantly more than plots with canopy cover < 50 % (p < 0.05). In middle elevations, no differences were observed between the plots, while in high elevation (i.e. with low traffic) the distresses of improper cross-section, area of ruts, and loosing aggregate plots with canopy cover > 50% were significantly higher than plots with canopy cover < 50 % (p < 0.05). No difference was observed in other variables. The results of this study showed significant differences in about half of the studied indices between shaded and non-shaded regions, yet the change in traffic variable did not determine any decreasing or increasing trend of shadow effect on road pavement quality.