Effects of Dispersed and Aggregated Retention Forestry and Small-sized Clear-cuttings in Conifer Plantations on Carabid Beetle Assemblages

Abstract

Retention forestry and small-sized clear-cutting are thought to mitigate logging impacts. In the Sakhalin fir plantation stands which were subjected to these logging operations and whole clear-cuttings 1-3 years ago and unharvested― we collected carabid beetles that are thought to respond to changes in forest environment. We trapped beetles using 1-3 fish baited pitfall traps for about 110 days at each stand. Logging operations clearly affected the beetle assemblages because the species compositions of beetles differed between the harvested and the unharvested sites. The species compositions in the dispersed retentions of naturally-regenerated broadleaved trees were between those of unharvested sites and clear-cutting sites, and the total abundance of forest beetle species significantly increased with the amounts of retained trees. The total abundance and species richness of forest species largely differed among the stands in the 0.36-ha unharvested patches of aggregated retentions and these were not different between ca 1 ha and 6-8 ha sized clear-cuts. Thus, we concluded that dispersed retention is a beneficial tree harvesting method that mitigates logging impacts, but also that further studies are needed to evaluate other types of operations. The species richness was slightly fewer than those from another study conducted at the same sites but with different methods (i.e., 20 non-baited pitfall traps for a total of 21 days at each stand one year after logging) but the number of beetles caught per trap per day was same.