Abstract
Weed invasion of natural forests due to recent increases in their use as recreational sites poses a problem affecting forest preservation. This study examined the effects of passage for recreational activities on the occurrence of weeds in forests. Weeds were surveyed in disturbed and undisturbed areas along both roads and naturally formed walkways in a temperate secondary forest located at Ashiu Forest Station, Kyoto University. Weeds were generally observed in the disturbed areas, with the greatest amount and highest species number observed along the roads. Based on the life-form classification of the weeds, species that appeared to invade easily tolerated physical pressure and dissemination by humans, vehicles, and wind along roads but only dissemination by humans along walkways. Among the environmental factors considered, light intensity and soil moisture, which were negatively correlated with each other in the road area, differed significantly between road and walkway areas. For the road area, there tended to be fewer weed species with increasing relative light intensity. This unexpected tendency might be due to the greater open space in the areas with more light, where wind and drier conditions suppressed weed growth. There were more weed species on the road surface than on slopes adjacent to the roads, and more on the walkways than on the adjacent undisturbed areas, where there were no weeds. As these differences could not be explained by the difference in dissemination frequency, changes in soil characteristics resulting from the physical pressure of repeated trampling by people or from vehicle tires were thought to be involved.
