We carried out a survey of ground beetle assemblages (Coleoptera: Carabidae and Brachinidae) using unbaited pitfall trapping in riparian forest dominated by broad-leaved trees and bamboo along the Inukami River, Shiga Prefecture, Japan, to elucidate the possible impact of bamboo culm thinning on ground beetle species diversity. Ground beetles were captured once a week at four experimental plots each with different bamboo culm density treatments; clear cut of all culms (CC), heavily thinned, lightly thinned and control, during July to December, 2010.

Species richness of ground beetles was the highest in the CC plot, while other plots did not different from each other. In addition, detrended correspondence analysis revealed that the species composition at the CC plot was divergent from the other plots. The characteristic species in the CC plot were Harpalus spp., Chlaenius variicornis and C. naeviger. The former two species are known as open habitat species, contributing to the higher species richness and the characteristic species composition. These results showed that removal of bamboo culms in broad-leaved forest had a positive impact on the species richness assemblages of ground beetles primary due to the increase of the open habitat species.