Community Development Pathways

Fungi colonizing wood are first faced with the problem of arrival at and entry into a suitable resource. Subsequently the priority is establishment within that resource, which at the earliest stages of community development may be uncol-onized by other fungi, but is most commonly against a backdrop of well-established mycelia. Once established, remaining within the resource depends on defence of territory held. Eventually, as the wood resource rots away, decay fungi need to exit in search of new resources, and the life-cycle continues.

Community development can begin under highly stressful conditions, under conditions where abiotic stresses are completely absent, or under conditions somewhere between these extremes. Such microenvironmental factors are strong determinants of the communities that develop (see below). Following initial establishment, community development is influenced by four main driving forces: stress aggravation (worsening of abiotic environmental conditions), stress alleviation (improvement in abiotic conditions), disturbance and combat (interspecific competition for space rather than directly for nutrients) (Figure 2; Cooke and Rayner, 1984; Rayner and Webber, 1984; Rayner and Boddy, 1988; Boddy, 2001; Heilmann-Clausen, 2001). Stress aggravation and alleviation is often brought about externally, e.g. improvement or worsening of water regime by wetting or drying, though the organisms themselves can also effect changes, e.g. translocation of water into dry wood. Alleviation of stress allows fungi with a preponderance of R- and/or C-selected characteristics to predominate, whereas stress aggravation leads to predominance of species tolerant of that particular stress. As colonization proceeds leading to a closed community with no uncolonized territory available, organisms with more C-selected characteristics begin to dominate, and during these middle stages of decomposition, community change is mainly effected by the fungi themselves. As decomposition proceeds the wood resource is used up, and an increasing proportion of the nutrients are contained within living hyphae, bacteria and mesofauna. Little is known of the ecological forces most important during these stages of decay, but the well-developed micro- and mesofauna probably play a crucial role, both as grazers on mycelia and also as a potential food source for wood decay fungi. In small branches, there can be dramatic changes in the fungal community following invasion by invertebrates, away from domination by Basidiomycota (Swift and Boddy, 1984).

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