Are woodland key habitats more diverse than production forests?

NEWS | 2012-06-03

Four scientists from Sweden and Finland have recently conducted a systematic review of woodland key habitats. Their results confirm that such biotopes are usually more species-rich than ordinary production forests.

Deciduous swamp woods of this kind count as key habitats since they often contain red-listed species. Photo: Claes Bernes.

In Swedish forests, more than 80,000 woodland key habitats (WKHs) have been identified to date. These consist of small woodland areas where red-listed species are, or could be, found. WKHs may, for example, be patches of forest with a high proportion of old trees, fallen timber and dead wood: such areas are thought to contain more red-listed species than are normally found in areas of large-scale forestry. The term ‘woodland key habitats’ is used in Norway, Finland, the Baltic countries and Russia as well, although the definition may not be precisely the same as in Sweden.

However, opinions differ concerning the value of WKHs for environmental management. Several studies suggest that they serve as havens for red-listed species, while others have found no evidence that WKHs are appreciably richer in such species than ordinary production forests. A Finnish and Swedish research group has therefore recently carried out a systematic review of biodiversity in WKHs. The group found a total of 18 studies — Finnish, Swedish and Norwegian — containing data of high enough quality to be used and compared.

More species in woodland key habitats

According to the review, the WKHs do in fact contain more red-listed species and also a higher aggregate total of species than surrounding production forests. Moreover, they have a larger and more varied stock of dead wood. Somewhat surprisingly, the divergence in species richness between WKHs and production forests proved to be larger for vascular plants (which seldom depend on dead wood) than for saproxylic beetles (which inhabit dead or decaying wood).

There are also some differences among various countries’ results. Swedish key habitats, for example, contain significantly more red-listed species than adjacent production forests, but in Finland the corresponding difference is not statistically significant. This may be because the two countries’ definitions of ‘key habitats’ differ slightly. Finnish key habitats are, moreover, extremely small areas — averaging only 0.7 ha — while the corresponding average in Sweden is 4.6 ha.

The research group also tried to find out whether key habitats can retain their conservation value if surrounding production forest is felled and replaced by clearcut areas. Here, however, the scientific documentation proved inadequate. Only two of the 18 studies had compared key habitats surrounded by clearcut area with those that were surrounded by mature forest.

Positive experience of systematic reviews

Lena Gustafsson

The systematic review of biodiversity in WKHs has recently been published by the Collaboration for Environmental Evidence (CEE). One of the scientists behind the review is Lena Gustafsson, Professor of Conservation Biology at the Department of Ecology at the Swedish University of Agricultural Sciences (SLU).‘There are many advantages in the approach used in systematic reviews,’ Gustafsson says. ‘Searches of the literature are organised in a systematic way that can be described verbally, in qualitative and quantitative terms. You’re also inexorably forced to define your research question, including the impact and effects that are in focus. And you can get opinions on your protocol from two or three independent referees. One disadvantage is that it can all take considerably longer than a traditional literature review.’

Jointly with Katja Fedrowitz at the same department, Lena Gustafsson has now started working on a new systematic review. This will address the question of how far nature conservation is taken into account in forestry and, in particular, how the number of trees left standing after felling affects forest biodiversity.