Understanding the pattern of occurrence of an organism or population is largely a problem of identifying its realized niche. This task involves the identification of not only the space-time occupied by the organism in nature but also the role within that space-time during interaction with the biotic environment (Cooke and Rayner 1984). In turn, this leads to the problem of how best to classify the role of an organism. Apropos, appreciating the ecological (Andrews 1992; Pugh and Boddy 1988) and nutritional strategies displayed by individual fungi is a useful first consideration. Here I will consider the latter only.
An individual filamentous fungus may achieve an absorptive heterotrophic life-style via biotrophy or necro-trophy, either exclusively or sequentially. Fungal residents of woodland ecosystems exhibiting biotrophy include the (neutralistic to mutualistic to parasitic) endophytes and (mutualistic to parasitic) mycorrhizae, whereas archetypal necrotrophic representatives include certain (parasitic) pathogens and the decay saprotrophs of dead wood- and litter-tissues. These broad activity categories represent convenient but sometimes restrictive descriptors for the ecologist because they may obscure the dynamic nature of the relationship. In the next section I wish to avoid discussion on the boundaries of classification schemes, but will consider the wood-decay activities displayed by the associations mentioned above, so as to illustrate the spatio-temporal complexity and versatility of filamentous fungi. We as mycologists often focus on the wood-decay activities of true wood and litter saprotrophs, sometimes at the expense of recognizing the prevalence of such activities to other association habits. These association categories merely represent distinct points within a continuum of overlapping activity groups. Therefore, certain individuals may be classified simply as wood or litter inhabitants or as mycorrhizae, but others may decay both wood and litter, or may be mycorrhizal but also cause lignocellulose decay. Moreover, the nature of interactions between individuals may alter with life-cycle stage or environmental circumstances. An individual may thus commence as an endophyte, then develop as a latent pathogen, and subsequently adopt a more saprotrophic role, following senescence of the host. The specificity of relationships also varies. Consequently, some fungi will be restricted to a particular biome, geographic area, specific resource, host species, part or cell-type within a host species. Others may be nonselective, ubiquitous generalists, such as the opportunistic decomposers. Furthermore, mycelial patterns may operate over a range of scales, from an individual pine needle (Kendrick and Burges 1962), to an entire forest (Smith 1999) or even at a global scale (Arnolds
Finally, the heart rot and active pathogenic activities of fungi causing death and decay of standing trees was described in the first edition of this text and will therefore not be considered here (Boddy 1991). The structural, chemical, and microclimatic features prevalent in living wood and the biology, ecology, and epidemiology of fungi causing its decay have been reviewed elsewhere (Butin 1995; Rayner and Boddy 1988; Schwarze et al. 2000; Smith et al. 1992; 1999; Tainter and Baker 1996; Vasiliauskas 2001; Woodward et al.
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