Minimum patch sizes and suitable habitats are essential for polypore conservation

The 1992 Convention on Biological Diversity challenged national legislations and policies concerning the management of natural resources. In many countries, forest legislation and management guidelines were modified to increase consideration of biodiversity conservation. Traditional conservation means, such as the establishment of protected areas, were revised, and new methods, such as the protection of woodland key habitats and retention trees, were introduced to improve the ecological quality of commercial forests. At the same time, research regarding the ecological efficacy of different conservation means increased.

Dead wood is an important substrate for a large number of forest-dwelling species. One group of deadwood-dependent species that has gained special attention is the polypores (Basidiomycota: Aphyllophorales). Because polypores are dependent on dead wood, they are sensitive to measures that decrease dead wood availability and, consequently, polypores have been regarded not only as great losers in managed forests, but also as good indicators of conservation value. All these factors have contributed to the popularity of polypores as a subject of biodiversity studies during the 18 years following the Convention on Biological Diversity.

With this in mind, researchers at the University of Eastern Finland set out to review the accumulated information. In a review published in Biological Conservation, the researchers concentrate on boreal Europe (Fennoscandia) from which the majority of the polypore studies come from. The review involved a total of 76 articles, which represent fairly equally all sections of the boreal vegetation zone: in 31 articles, all or part of the data were collected in the northern boreal zone, and in 31, 24 and 26 articles in the middle boreal, southern boreal and hemiboreal zones, respectively.

Two main polypore conservation implications arise from the review. First, there seem to be thresholds for the minimum patch size, amount of dead wood and tree diameter at the stand scale. At the stand scale, the amount of dead wood is the strongest determinant of polypore species richness; the minimum average amount of dead wood for the occurrence of rare polypores appears to be 20–40 m3/ha. Species-area analysis shows that in mature boreal forests species accumulation levels off at around 20–30 ha. This led the researchers to suggest a heuristic 20/20/20 rule of thumb: a 20 ha stand, with an average of 20 m3/ha of dead wood of which many are logs >20 cm, is likely to be the minimum for the ecologically justified conservation of polypore diversity at the stand scale in boreal Europe.

Secondly, the researchers concluded that equally crucial for polypore diversity is the current and historic extent of suitable habitats at the landscape scale. The time lag between the isolation of a habitat patch and the new equilibrium in the number or occurrence of species seems to be around 100–150 years, indicating that an extinction debt is likely to exist in recently isolated fragments. Only a few studies have addressed the ecological efficiency of the new, biodiversity-oriented forest management tools (retention trees, woodland key habitats). Despite this it seems that the traditional large conservation areas are the most effective means of polypore conservation.


For further information, please contact Kaisa Junninen, tel. +358 13 251 4064, email: kaisa.junninen@uef.fi


Original article:
Junninen, K. & Komonen, A., 2011. Conservation ecology of boreal polypores: A review. Biological Conservation 144: 11-20.
 

Artikkelin kirjoitusvuosi: 2011

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