In several countries grassland fungi have been proposed as indicators of valuable grassland localities. Rald (1985) suggested that the number of Hygrocybe species (including Camarophyllus) found in a locality was a good indicator of the myco-logical importance of the locality: localities with 17 species or more were of national importance, and sites with fewer species were of local, regional or no importance (Table 2). Rald and Boertmann (1989) found that 12 Danish localities qualified as being of national importance. Ten years later the number had increased to 35, due to extensive field work (Vesterholt et al., 1999), while 12 Danish grassland localities with 22 Hygrocybe species or more were considered as being of international importance following Rald (1985).
The exact habitat requirements of most grassland fungi are still poorly understood (Chapter 14), but it is broadly accepted that some grassland species are better indicators of valuable grassland localities than others. Such good indicators are typically rare and restricted to localities with high species diversity. Some of the grassland species seem to occur only in old grasslands with a long continuity, e.g. Entoloma anatinum, E. longistriatum, E. mougeotii, Hygrocybe intermedia, H. citrinovirens, H. ovina, H. aurantiosplendens and H. ingrata (McHugh et al., 2001; Vesterholt, 2002; Newton et al., 2003). On the other hand, some rare species, e.g. Entoloma formosum, E. hispidulum, E. xanthochroum, Hygrocybe sub-papillata, H. glutinipes, H. vitellina and H. spadicea are also found in grasslands with a shorter continuity. Based on such experiences, Jordal and Gaarder (1993) proposed a classification system, where an individual indicator value was assigned to each grassland species, from 0 to 8 points, so that the value of a locality was calculated by summing the value assigned to each of the species found in the locality. The system includes several groups of fungi, and it is therefore more broadly applicable than the systems based only on Hygrocybe species, which is important since grasslands are sometimes richer in Entoloma than in Hygrocybe
Table 2 Erik Raids system for classification of dry grassland localities, amended by Vesterholt et al. (1999)
Of limited importance 1-3 Hygrocybe species
Of local importance 4-8 Hygrocybe species
Of regional importance 9-16 Hygrocybe species
Of international importance > 22 Hygrocybe species species (Newton et al., 2003). A similar system has been suggested by McHugh et al. (2001) for Irish grassland fungi where each species is given an indicator value on a scale from 1 to 4 points.
Grassland fungi do not fruit in abundance every year, and some species fruit after intervals of several years. This is especially the case with many Entoloma species that fruit mainly in the summer. Thus, it is necessary to visit a locality several times, and preferably at least once in a very good season, to assess the real value of a locality. Accordingly, Rald's (1985) method of classifying a site after a single visit is not recommended.
Saproxylic fungi constitute a highly diverse group, comprising thousands of species in Europe (Chapter 11). Well-known, species-rich groups include poly-pores and corticoid basidiomycetes, but also agarics and pyrenomycetes and many others. Unlike grassland fungi, saproxylic fungi are associated with naturally relatively short-lived resources that are spatially restricted. Therefore, individual mycelia are usually short-lived (<100 years, often much less), good dispersal ability being paramount for survival in the long run. Some, e.g. cord-and rhizomorph-forming basidiomycetes, may however become very old and large (e.g. Ferguson et al., 2003; Chapter 1). Under natural conditions dead-wood habitats are common. Thus, dispersal over relatively short distances (1-1,000 m) is more important than over longer distances. Nevertheless, spores of several saproxylic species have been shown to be able to germinate after travelling hundreds or even thousands of kilometres from their source (Vilgalys and Sun, 1994; Hallenberg and Kuffer, 2001).
Little is known of population densities of wood decay fungi. The few studies conducted so far have demonstrated that the number of mycelia in unit-restricted fungi is often higher than expected from the distribution of sporocarps. Thus, single pieces of dead wood are commonly inhabited by several individuals of the same species (Boddy and Rayner, 1983; Hendry et al., 1998; Kauserud and Schumacher, 2002, 2003). Also, most living trees host saproxylic fungi resting latently, waiting for appropriate conditions for active growth (Chapter 11). Population density is therefore underestimated by sporocarp surveys. On the other hand, dead-wood communities are often very species rich pointing to a high level of niche differentiation (Heilmann-Clausen et al., 2005).
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