Abstract
We investigated changes in understory vegetation after heavy thinning in hinoki plantations in Shikoku Island, Japan. We observed the abundance and species diversity of understory vegetation at two experimental sites (Furumiya and Tengu) for 6 years after thinning, where approximately 25% and 50% of trees were removed. Thinning increased the understory vegetation cover at both sites. In the heavily thinned (50%) plots, species richness, and cover and height of individual plant species also showed considerable increase. Although vegetation cover and height increased continuously for several years, species richness increased rapidly in the first year after thinning. The diversity index also increased in the first year and then decreased during the following years. This suggests that newly established species mainly emerged in the first year after thinning, and the following increase in the vegetation cover was caused by the growth of some component species. The Tengu site exhibited a larger increase in vegetation height and species richness, and greater change in species diversity and composition in the heavily thinned plot than did Furumiya. These differences between the sites may have been caused mainly by less initial understory vegetation at Tengu. Differences in climate and land use history may have indirectly affected the change in understory vegetation.
