Fragmentation Effects

Within a metapopulation context the decline and fragmentation of dead-wood habitats is likely to cause a decline in species-diversity of wood-inhabiting fungi. Based on general species-area relations, Sittonen (2001) estimated that the observed decrease in available cwd in Fennoscandia is likely to cause a regional species loss of at least 22-32% in the long run. A comparable estimate for potential species loss was given by Berglund and Jonsson (2001) based on extrapolations from field observations of sporocarps in a natural forest wetland mosaic in northern Sweden. In contrast to Fennoscandia, where the loss of dead-wood habitats is fairly recent, the decrease in cwd has a longer history in the landscapes of Central and Western Europe. Even if the Scandinavian estimates of possible extinctions are overestimates, by failing to account for local survival of populations in protected forest reserves, it still seems likely that many wood-inhabiting species have suffered extinction in the deciduous forest zones of Europe, or at least have a much more restricted distribution than under natural conditions.

Fragmentation is likely to be most detrimental to species allocating limited energy to long distance dispersal, that is competitive and stress-tolerant species (see Chapter 11), though effective local dispersal may counteract this tendency in small areas with plentiful appropriate habitats. There are, unfortunately no available data to test whether allocation to spore dispersal differs between wood-decay fungi having different ecological strategies. It has been suggested that poor dispersal ability is a trait of species adapted to persistent and predictable habitat types with a random distribution pattern in the primeval landscape, while species depending on naturally patchy or temporally discontinuous habitats are assumed to have good dispersal abilities (e.g. Nilsson and Baranowski, 1997). Therefore it can be speculated that fungi depending on old living trees, presenting a very common and persistent habitat in primeval forests, are more likely to have poor ability for dispersal, compared with species living on decaying dead wood on the forest floor (a very common, but less persistent habitat), while species depending on highly patchy habitats, for example burned wood, are predicted to be superior dispersers. There is some evidence from boreal forests that such differences in dispersal potential occur. Thus, species confined to pine tend to be less sensitive to habitat fragmentation than species growing on spruce (Stokland, 2001; Pentilla et al., 2006), which could reflect the fact that pine forests are more prone to natural forest fires than spruce-forests. Hence old-growth pine stands tend to occur more clumped in time and space and be more prone to sudden destruction, compared to the ecologically more stable spruce-dominated stands.

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