Effects of thinning on undergrowth and pollination in a Japanese cedar plantation ̶A case study at Afan Woodland and the adjacent conifer plantation forest̶

Abstract

Twenty seven percent of Japan is covered by plantation forests of evergreen conifers. Studies on forestry in Japan have emphasized forest productivity, while biodiversity conservation has not been well studied. The present study tried to find the effects of thinning on undergrowth and pollination in a Japanese cedar plantation. Thinning improved the light condition of the forest floor. SDR (Summed Dominance Ratio) of the undergrowth in the thinned cedar forest was 1.7 times greater than that in the cedar forest without thinning, and 4.5 times greater in the second year. Pioneer shrubs and large forbs typically growing in open habitats greatly increased by thinning. Thinning also increased insectpollinated flowers and pollinator visits, which were quantitatively similar to those in a deciduous broadleaved forest. In contrast, no pollination was observed in the cedar forest without thinning. This study suggests that biodiversity is recovered by thinning the Japanese cedar plantation forest.