The response of bats to dispersed retention of broad-leaved trees in harvested conifer plantations in Hokkaido, northern Japan

Abstract

The area of tree plantations has been expanding globally. While plantations generally support less biodiversity than natural forests, the habitat function of plantations can be enhanced by management. Retention forestry is a promising method to mitigate the negative impacts of harvesting on forest-dependent species through retaining some vital habitat structures for organisms. Bats are highly dependent on forests and have an important pest-control function; however, their response to retention forestry remains unknown. We surveyed bat activity at clear-cut sites, sites with dispersed broad-leaved tree retention (medium-level retention: 50 trees/ha, high-level retention: 100 trees/ha), and unharvested Todo fir (Abies sachalinensis) plantations in Hokkaido, northern Japan. We analyzed the effects of these treatments on genus richness and the activity of three groups preferring different degrees of habitat openness (cluttered-space species, open-space species, and edge species). Genus richness and the activity of cluttered-space species were higher at retention sites than at clear-cut sites. Similarly, the activity of edge species was higher at high-level retention sites than at clear-cut sites and comparable to that at unharvested plantations. Unexpectedly, the pattern of open-space species was similar to that of edge species. The increase in bat activity due to high-level retention was predicted to be 3.4 and 6.1 times that of medium-level retention for cluttered-space and edge species, respectively. Our results imply that dispersed broad-leaved tree retention in conifer plantations mitigates the negative impacts of harvesting on cluttered-space and edge species, and high-level retention is more effective. Thus, retaining large numbers of trees in a few harvested compartments and clear-cutting in others can be more effective for conserving bat activity than retaining a smaller number of trees in each of many compartments. For biodiversity conservation in plantation landscapes, it would be worthwhile to consider not only the common strategy of low retention in each of many harvested compartments but also a management strategy that retains many trees in a few compartments.