Changes in Habitat Availability

Potential habitats for wood-inhabiting fungi have decreased considerably almost everywhere in Europe during the last 2-5 millennia, due to forest clearance and cutting operations in extant forests. The extent of decline in forest cover differs markedly between countries and regions: current forest cover in the deciduous forest zone in Europe varies between 8% of the land area in Ireland to about 50% in Austria, Bosnia-Herzegovina and Greece (Parviainen, 1999). The amount of dead wood in long-established European beech forest reserves has been reported to average between 131 and 220 m3/ha, in lowland and highland areas respectively, while managed stands in the same regions typically contain less than 10 m3/ha (Christensen et al., 2005). Thus, beech forest reserves typically contain at least 10 times the amount of woody resource present in similar managed stands in temperate Europe. If these values are generalised to be representative of other forest types in temperate Europe, habitats for wood-decay fungi can then be estimated to have suffered a decrease of 90-99.5% at the landscape scale. Within countries the extent of decrease is much more variable, with urbane and highly cultivated regions showing an even higher decline, while remote mountain forest regions generally have suffered a more modest change.

Apart from the overall decline in available resources, wood-inhabiting organisms are also faced with fragmentation of suitable habitat patches. This is evident both at the local scale, where management in most forests has increased distances between individual wood units (especially for large diameter wood) and at the regional scale, where remaining forests typically form more or less isolated patches in a matrix of farmland and urban areas. At the European scale the most extensive deciduous forest areas, including the majority of coarse woody debris (cwd) rich forest reserves, are restricted to mountainous parts of Eastern, Central and South Europe (Christensen et al., 2005).

In addition to the decrease and fragmentation of cwd habitats there has been a shift in general forest composition. In most parts of Europe, forestry has favoured conifers to the detriment of deciduous tree species, and at the same time forest management has focussed almost exclusively on timber production. Forestry activities deliberately remove certain wood types; especially logs and larger branches, while twigs and cut stumps are mostly left for natural decay. Managed forests thereby present a smaller, but also different, selection of microhabitats for saproxylic organisms compared to unmanaged forest (Figure 1). It is noteworthy that many, now vanishing, traditional forest practices had a very different impact on dead-wood habitats compared to modern forestry. Most notably, forest grazing (wood pasture) allows or even favours the presence of old trees, due to their high mast or leaf production, and along with pollarding, results in high densities of old trees with heart-rot or dead parts, even compared to long unmanaged old grown forest reserves (Figure 2).

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