Ecological impacts of fungal wood decay types: A review of current knowledge and future research directions

I summarize current knowledge about the ecosystem functions of wood decomposition in forests with a particular focus on the effects of fungal wood decay types (traditionally categorized into white-, brown-, and soft-rot) on the community composition of saproxylic organisms, forest tree regeneration, and carbon sequestration. Deadwoods of different decay types show markedly different physicochemical and biological properties. High carbohydrate availability in white-rotted wood promotes the activities of nitrogen-fixing bacteria; thus white-rotted wood is a good dietary source for many wood-eating invertebrates. In contrast, brown-rotted wood is unattractive to saproxylic communities due to the high recalcitrance of accumulated lignin, low nutrient content, and low pH. Nevertheless, some species have adapted to these conditions and form distinctive communities on brown-rotted wood. Tree seedlings that are associated with brown-rotted wood are symbiotic with arbuscular and ericoid mycorrhizal fungal species, but not ectomycorrhizal species. Thus, the diversity of fungal communities associated with a variety of wood decay types produces habitat diversity for saproxylic communities and promotes biodiversity in forest ecosystems. Wood decay type also affects carbon sequestration in forests as brown-rotted wood might be more instrumental in soil organic matter accumulation than white-rotted wood. An important aspect of wood decay type is that the wood decay activities of fungi can have indirect long-lasting cascading impacts on forest biodiversity by altering the physicochemical properties of deadwood. Including the effects of wood decay type in ecological models is thus important for predicting the long-term dynamics of biodiversity, vegetation, and carbon cycling in forest ecosystems.