Hotspots in a cold climate – are woodland key habitats biodiversity hotspots? (systematic review)
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.
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.
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 Researchers with much experience of WKH research were also contacted to obtain possible unpublished literature.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.
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.
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.
Forests in the Fennoscandia and Baltic countries have a long history of human utilization. From the beginning of the 20th century forest harvesting methods shifted from selection felling towards clear cutting. Modern, highly mechanised forestry with clear cutting, intensive silviculture, thinning of regenerating stands and short rotation times, has been employed in Fennoscandia since 1950s and in the Baltic countries since 1990s. Because in Fennoscandia and Baltic countries the majority of the forests are commercially managed conservation of biodiversity critically depends on management actions that take place in the production forests, i.e. in areas outside forest reserves. Hence, the focus of conservation has shifted towards multiscale conservation measures (Lindenmayer and Franklin, 2002). In addition to large ecological reserves, intermediate- and small- spatial scale conservation measures, such as biological hotspots and green tree retention, respectively, are taken place in the matrix.
One tool for intermediate-spatial scale conservation of the forest biodiversity is the conservation of small habitat patches called Woodland Key Habitats (WKHs). The concept of WKH was coined in Sweden in the early 1990 ́s. Nitare and Norén (1992) described WKH as a habitat where red-listed species occur or are likely to occur. The concept is based on two assumptions. First, red-listed species are assumed to be clustered into certain sites or habitats rather than to occur evenly or randomly in the forest landscape. Second, it should be possible to identify WKHs by their structural features and indicator species and thus direct observation of red-listed species would not be necessary.
The concept of WKH has been adopted from Sweden to Finland, Norway, Denmark Latvia, Lithuania, Estonia, and Russia. WKH concept has become an important instrument in the conservation of forest biodiversity and large scale WKH inventories have been conducted nationally. There have been debates over the importance of WKHs, and the results of the existing studies have been controversial (Gustafsson et al, 1999; Gustafsson, 2000; Johansson and Gustafsson, 2001; Sverdrup-Thygeson, 2002; Gustafsson et al 2004; Pykälä et al 2006).
Small sites such as WKHs might have difficulties to retain their original species composition and support species persistence over time since clear cutting, the prevailing logging method, in the surroundings may cause changes in the microclimatic conditions due to increased exposure to sunlight and wind. Consequently, studies on edge effects are relevant when the efficiency of WKHs is to be evaluated. The aim of our review is to summarize knowledge on WKHs with special focus on comparisons of biodiversity qualities between these presumed hotspots and surrounding production forests. We will also summarize the knowledge on the impact of edge effects. To really evaluate the status and validity of WKHs as biodiversity hotspots, and thus a sound conservation tool, a systematic review is well argued.