Responses of boreal ground beetles (Coleoptera, Carabidae) to different logging regimes ten years post harvest

Abstract

Most investigations of human impacts on biodiversity have been conducted within 1–3 years post-disturbance, although many biological responses develop over a longer period of time and annual community variation cannot be fully controlled. We therefore conducted a follow-up of carabid beetles over ten years in Norway spruce (Picea abies) dominated forests in Southern Finland, harvested using replicated logging treatments of different intensities. We collected carabids using pitfall traps in 1995 (prior to logging) and during four post-harvest seasons, 1996–98 (three first post-harvest summers) and 2006 (ten years after harvesting). The treatments were clear-cutting (no retained trees), modified clear-cutting (retention of three groups of 20–30 trees within a one-hectare plot) and gap cutting (three 0.16-ha openings within a one-hectare plot), and control (mature unharvested forest). (1) Total species richness and open-habitat carabids increased in gaps and in the two clear-cutting treatments, whereas forest carabids were slightly less abundant in clear-cuts than in the other treatments in 1997. These patterns were most evident in the second and third post-harvest summers. (2) Open-habitat carabids were less abundant and less speciose in both cleared and retained patches of gap cuts than in clear-cuts, Pterostichus adstrictus was more abundant in clear-cuts than in retained patches of modified clear-cuts or gap cuts, and carabid assemblage was more altered in both types of clear-cut than in gap cuts. (3) Ten years after logging, open-habitat carabid numbers were still elevated, whereas Calathus micropterus was less abundant, in the two types of clear-cut than in gap cuts or control stands. (4) We also found remarkable annual variation in carabid assemblages, such that was independent of logging. We conclude that even modest retention provides long-term support for forest carabids, but also that their full assemblage recovery takes longer than 10 years.