Are woodland key habitats biodiversity hotspots in boreal forests?

Background: The concept of Woodland Key Habitats (WKH, small-scaled presumed hotspots of biodiversity) has become an essential component of forest management in Fennoscandian and Baltic countries. There have been debates over the importance of WKHs in relation to production forests, and several research projects have focused on differences in biodiversity between the two. Results have been contradictory, and thus there is a need to summarize and clarify the existing knowledge. - Objectives: Our objective was to summarize knowledge on comparisons of several biodiversity qualities between WKHs and production forests in relevant countries i.e. the countries where WKH concept has been implemented. We also summarize the knowledge on the impact of edge effects on WKHs by comparing WKHs surrounded by mature forests to WKHs surrounded by clear cuts. - Methods: We conducted searches in multiple databases and in Google Scholar after the keyword scoping. Main institutions in Sweden (Swedish Forest Agency) and Finland (Forestry Development Centre Tapio and Metsähallitus) with activities on WKHs were also consulted through personal contacts and web-page searches. Researchers with much experience of WKH research were also contacted to obtain possible unpublished literature. We conducted meta-analysis with the data extracted from the original studies that were included it the review. - Main results: Studies had been conducted in Finland, Norway and Sweden. Total number of studies found from databases was 1443. Forty studies remained after the abstract filter stages. Finally, 18 studies were included in the review, from which 16 studied the differences between WKHs and production forests, and only two studies compared WKHs surrounded by mature forests and WKHs surrounded by clear cuts. Our results suggest that WKHs seem to be hotspots of dead wood, diversity of dead wood, species richness and red-listed species. Also, we found differences between countries in these biodiversity qualities. - Conclusions: Our results suggest that WKHs seem to be biodiversity hotspots. However, there are not enough studies focusing on how WKHs are able to maintain these biodiversity qualities when surrounded by clear cuts. Indeed, landscape scale issues, such as proximity and extent of clear cuts, may be reducing WKHs contribution to the conservation of biodiversity. As such this area needs further investigation.