Influences of Seibu Road on the World Heritage Forest of Yakushima Island, Japan

The area of World Heritage in the northwest of Yakushima is the only part of the island where natural vegetation still extends to the coast. The influence of the Seibu Road (19.3km) on this forest was investigated using three indicators. The first was physical discontinuity of the forest (P), which was determined from the lengths of artificial slopes above and below the road. The second was scenery disturbance (S), which was determined from the presence or absence of trees beside the road. The third was vegetational disturbance (V), which was determined from the number of invader plant species found alongside the road.In section of the road where has been relatively little disturbance the tree tops meet to form a “Green Tunnel”. The occurrence of such “Green Tunnel” sections was recorded continuously along the road.Discontinuity of the forest (P) was significant positively correlated with both scenery disturbance (S) and vegetational disturbance (V), such that section of the road which have been most developed have the least roadside trees and the greatest number of invader plant species. “Green Tunnel” existed along only one fourth of the whole length of the road and along only one third of the road within the World Heritage forest. Almost all of “Green Tunnel” sections were found in the Hanyama and Kawahara areas, where all three indicators also showed the low disturbance.These results suggested that, in order to conserve the natural environment of the World Heritage forest, the construction of artificial slopes above and blow the road should be avoided as far as possible.