NATURAL REGENERATION AND ARTIFICIAL THINNING FOR EARLY FOREST RESTORATION ON A PERMANENTLY CLOSED SKI SLOPE

In recent decades, numerous ski resorts in Japan have had to close due to financial difficulties. Forest restoration on these abandoned ski slopes is necessary for landscape management and to prevent avalanches and landslides. However, forest restoration activities are hindered by the scarcity of nutrients due to topsoil removal at the time of ski slope construction. In this study, the effect of thinning on alleviating competition for soil nutrients was examined. The study site was located on Mt. Tateshina in central Japan. The study site's ski slope was closed permanently in 1997, and the first natural regeneration of larch occurred in 1998. Chubu Regional Forest Office performed artificial thinning in 2003. Two thinned, nine un-thinned quadrat plots in 2016 were established and measured the total height and diameter at all living and dead trees' breast height. Tree-ring analysis of nine sample trees in each of the un-thinned and thinned plots at 1 m height intervals was performed to clarify tree growth. The un-thinned field had a high tree density, small tree size, and numerous dead trees, suggesting the existence of severe competition. Conversely, the thinned plot was characterized by a lower tree density, large tree size, and fewer dead trees. According to the tree-ring analysis, artificial thinning improved the survival rate and smaller trees' growth rate. It was concluded that the artificial thinning of natural forests on ski slopes is useful for accelerating tree growth and early forest development.