Deadwood and saproxylic beetle diversity in naturally disturbed and managed spruce forests in Nova Scotia

Even-age industrial forestry practices may alter communities of native species. Thus, identifying coarse patterns of species diversity in industrial forests and understanding how and why these patterns differ from those in naturally disturbed forests can play an essential role in attempts to modify forestry practices to minimize their impacts on native species. This study compares diversity patterns of deadwood habitat structure and saproxylic beetle species in spruce forests with natural disturbance histories (wind and fire) and human disturbance histories (clearcutting and clearcutting with thinning). We specifically examine how beetle diversity differs in relation to disturbance history and how beetle variation is linked to the diversity of deadwood habitats. Beetle and deadwood data were collected from thirty spruce forests in Nova Scotia and analyzed under three related diversity perspectives: alpha (diversity within local forests); beta (heterogeneity among local forests within disturbance classes); and gamma (cumulative species richness within disturbance classes). Few data support a prediction of lower alpha deadwood and beetle diversity in managed forests, or a prediction of lower gamma species richness in managed forests. The beta scale analysis yielded support for the following two hypotheses: (1) beetle assemblages are different in forests with different disturbance histories; (2) turnover of beetle assemblages is higher among naturally disturbed forests than among managed forests. The prediction of lower gamma diversity of saproxylic beetle species in managed forests compared to naturally disturbed forests was not supported. The lack of differences between naturally disturbed and industrial forests in structures that are characteristic of older forests (e.g., large-diameter deadwood) may relate to the presence of residual deadwood in second growth forests lingering from before clearcut harvesting. However, such residual deadwood is only an artifact that will soon decay and not be replaced. This suggests that the continuity of deadwood microhabitats for species that depend on old-forest structures is only short-term.