Initial Changes in Ground Beetle (Carabidae: Coleoptera) Assemblages after Creating Gaps of Varying Sizes in Mature Northern Hardwoods Forests in Wisconsin

Managers of northern hardwood forests in the Great Lakes region create gaps in the forest canopy of various sizes during harvesting to achieve different silvicultural objectives. Single-tree harvesting favors recruitment of shade-tolerant tree species by creating small gaps in the canopy, whereas group selection creates larger gaps that can favor shade-intolerant tree species. We evaluated changes in carabid beetle abundance and diversity in harvest-created gaps of five sizes (gap diameters of 6, 10, 20, 30, and 46 m) and uncut forests in northern Wisconsin where sugar maple (Acer saccharum) was the dominant tree species. Gaps were cut during the fall/winter of 1994 and 1995. Pitfall traps were used to sample carabids during the summers of 1994 (pre-harvesting) and 1997 (2nd or 3rd summer post-harvesting). Overall, 27,111 carabids (60 species) were collected in both years, with 15,036 (25 species) collected in 1994 and 12,075 (55 species) collected in 1997. Carabid species richness increased while catch rate decreased with increasing gap size. Similarly, as gap size increased, carabid abundance declined for forest specialists but increased for open-habitat species. The carabid assemblages in the 6- and 10-m-diameter gaps were most like the intact forest, while those in the 30- and 46-m-diameter gaps were most distinct. Results are discussed in terms of harvesting strategies in northern hardwood forests to maintain high biodiversity.