Spatial and temporal changes of vegetation cover in granite mountains in central Japan: a GIS‐based approach

Abstract

AbstractDegraded hillslope areas are widespread in the Tanakami area located in Shiga Prefecture of central Japan as a result of more than 1300 years of human impact. Consequently, accelerated erosion rates and high storm runoffs have been major environmental problems there. To attempt to stabilize hillslopes and to reduce sediment and water discharges, extensive reforestation projects have been conducted since the 1870s. The vegetation recovery in the Tanakami area over a 51‐year period was assessed using a geographic information system‐based approach. The results showed that, in the areas where only hillside planting work was conducted, the percentage of bare slope area increased mainly due to the destruction of the vegetation cover on the forested slopes with gradients exceeding 30 degrees, and/or on southwest and northwest slopes. Moreover, the destruction of vegetation cover on steep slopes was seen to be most prevalent where hillside planting work was conducted without slope terracing. In contrast, in the area where both hillside planting and tending works were implemented, the bare slope area tended to decrease through the study period. Consequently, in 1988, there were only 1 per cent of bare slopes in the area where both hillside planting and tending works were implemented; in contrast the bare slope areas where only hillside planting work was conducted still occupied 12–17 per cent. These results imply that the reforestation practices that include hillside planting and tending works, or at least slope terracing, are necessary to prevent the destruction of the vegetation cover on steep southwest and northwest slopes. Copyright © 2002 John Wiley & Sons, Ltd.