Effects of vegetation type and horizontal curve radius on the rate of tree pruning to provide line of sight on main access roads

Abstract

The present investigation was carried out to assess the influence of vegetation type and horizontal curve radius on the rate of tree pruning to provide the line of sight on horizontal curves in Caspian forests of Iran. For this purpose, the DBH (diameter at breast height) of trees around the curves which must be pruned was measured. Also, the horizontal curves radius was divided into 4 classes and for each class 10 horizontal curves (for each species) were selected and the species which required pruning were measured. The rate of radial pruning was determined to provide a minimum stopping sight distance by means of laser rangefinder along the line of sight. We found an inverse relationship between DBH and the rate of pruning. To provide sight vision, the radial pruning rate decreased regularly with the increasing radius of horizontal curves for coniferous species, while it increased irregularly for broadleaves. There was a significant difference in pruning between different radii of horizontal curves (P < 0.05). According to results, pruning should be done for mixed hardwood trees with widespread crowns and no sharp horizontal curves should be designed at the top or bottom of hills.