Decay in Fallen Twigs and Small Branches

Fungal communities in fallen twigs and small branches have not been well studied, but based on sporocarps there appear to be large differences in species composition compared with more bulky resources (Norden et al., 2004b). In early decay stages differences relate to the pre-fall infection history. At fall twigs are typically dominated by Ascomycota and corticoid Basidiomycota several of which developed from latent propagules, e.g. Hypoxylon spp. (Ascomycota), V. comedens and Peniophora spp. (Griffith and Boddy, 1988,1990; Boddy and Griffith, 1989).

Small diameter dead wood provides much less stable microclimatic conditions than larger wood, being highly prone to desiccation and temperature fluctuations (Boddy, 1983), which will affect both species composition and decomposition rate. In a microcosm study, fluctuating microclimatic regime enhanced both species diversity and decay rate (Toljander et al., 2006). In the field, the decay rate of small diameter wood is faster than large diameter wood (Stone et al., 1998; Tarasov and Birdsey, 2001), which could indicate that overall conditions for decay are more favourable in small diameter wood, reflecting better aeration and less allelopathic chemicals than in larger wood, and/or may relate to differences in species composition. Thus, fallen twigs are often rapidly colonized by cord-forming Basidiomycota (Boddy, 1993), which are known as fast and effective decayers. Due to the relatively fast decomposition of small diameter wood, complex interactions between decay fungi, ectomycorrhizal fungi and invertebrates appear to be less distinct or at least to occur for shorter time than in bulky resources, and many late stage specialists reported from logs and large branches seem to be absent from twigs and small branches, based on sporocarp evidence (Kruys et al., 1999; Sippola and Renvall, 1999).

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