The influence of forest management systems on the abundance and diversity of bark beetles (Coleoptera: Curculionidae: Scolytinae) in commercial plantations of Sitka spruce

Abstract

Sitka spruce is the most widely planted conifer tree species in the UK, and is generally grown in dense monocultures managed using the clear-cut system. This study investigates the influence of alternative management systems (shelterwood and selection systems) on captures of bark beetles and associated predators. Bark beetle abundance was significantly lower in stands managed by shelterwood and selection systems when compared to mid (21–40years old) and mature (≥41years old) stands managed by the clear-cutting method. The abundance of bark beetles, including individual species, within plots could not be fully explained however, using linear mixed model analysis that not only included the various site characteristics assessed within each plot (numbers of live and dead trees), but also the numbers of predatory beetles (Rhizophagidae and Salpingidae). This suggested that the influence of management type on bark beetle abundance was not entirely due to the bottom-up or top-down forces that were assessed in the study, and that other abiotic and/or biotic factors were likely to be influential. Bark beetle diversity was also influenced by the management system, however higher diversity values within some group selection managed plots were only apparent in circumstances when stands of Sitka spruce had been managed using this system for a considerable period of time, and the habitat had remained undisturbed for a relatively long period of time (i.e. no harvesting interventions). Significantly higher numbers of predatory beetles were captured within the mid and mature clear-cut managed stands. The results from the study indicate that adopting alternative management systems to manage Sitka spruce in the UK could be a potential strategy to mitigate likely increases in bark beetle populations associated with climate change.