Conservation Status and Threats

The abundance and quality of dead-wood habitats has changed considerably through historical time in temperate Europe, and similar changes have occurred, or are happening in most other parts of the world. These changes can be summarised for temperate Europe (Chapter 11):

1. Decline in the amount of dead wood. The actual extent and timing of decline is highly variable among forest regions in Europe, ranging between 90 and 99.5% of that in primeval forests.

2. Fragmentation of remaining dead-wood habitats. 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 fractions), and at the regional scale, where remaining forests typically form more or less isolated patches in a matrix of farmland and urban areas. In Europe the majority of forest reserves rich in dead wood are restricted to mountainous and other cultivation-hostile areas.

3. Change in dead-wood composition, i.e. an increase in amount of coniferous wood and modified or cut wood, a modest decrease in small-diameter dead wood and a strong decrease in large-diameter wood.

The effects for communities of saproxylic fungi have been dramatic (Chapter 11): the decline in amounts of dead wood has resulted in a reduction in population size of most saproxylic fungi, most dramatically for species with a natural low population density. The change in availability of certain types of dead wood (e.g. large decomposing logs, dead wood in veteran trees) has resulted in a decline in species adapted to the conditions within these, while species with broad ecological amplitudes or adaptations to less decreasing or even increasing habitats (cut wood, small diameter wood, coniferous wood) has declined less or even increased. These trends are reflected in red-lists from several European countries, e.g. Sweden, where saproxylic fungi are over-represented among species showing a distinct preference for large-diameter decaying trunks or veteran trees (Dahlberg and Stokland, 2004).

New forest reserves have been declared in many European countries, as a response to the decline of dead-wood habitats and their associated biodiversity (Parviainen, 1999), and initiatives have been taken to increase dead-wood quantity in managed forests (e.g. Skov- og Naturstyrelsen, 2005). For some species these initiatives might come too late or be too limited to counteract further species extinctions, due to a lack of congruence between population and habitat dynamics, resulting in a so-called extinction debt (e.g. Jonsson et al., 2005). One example could be the polypore Hapalopilus croceus which is currently known from less than 150 sites in Europe, all with very low local population sizes (Dahlberg and Croneborg, 2006). The species is associated with very old living or decaying oaks, and even though dead wood is increasing in many landscapes, the specific habitat is highly fragmented.

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