The spatial distributions of understory trees in relation to dwarf bamboo cover in a cool-temperate deciduous broadleaf forest in Japan

Dwarf bamboo is a major understory vegetation in Japanese forests, and is recognized to be an ecological filter for the seedlings of overstory tree species. However, the effects of dwarf bamboo cover on the entire understory tree community, including shrubs, have not been fully assessed. Using spatial analysis by distance indices (SADIE), we analyzed the spatial distributions of, and the spatial associations between, Sasa palmata cover and understory trees (diameter at breast height < 2 cm, height a parts per thousand yen50 cm) in a cool-temperate deciduous broadleaf forest dominated by Fagus crenata. In a 20 m x 240 m area, we found 49 total species, among 11,686 stems. Cephalotaxus harringtonia var. nana, plus Lindera umbellata and F. crenata stems accounted for about 50 % of the overall total. The SADIE analysis based on 5 m x 5 m quadrats demonstrated that most species, among the 20 tree species we examined, showed significantly aggregated distributions (P < 0.05) and/or significant spatial dissociations (P < 0.05) with S. palmata cover. However, for C. harringtonia var. nana, L. umbellata, Meliosma tenuis, and Ligustrum tschonoskii, their spatial distributions were independent, or significantly associated (P < 0.05) with S. palmata cover. Our results indicates that dwarf bamboo acts as an ecological filter, not only for the seedlings of overstory tree species but also for other understory trees, in the cool-temperate deciduous broadleaf forest.