Soil macrofauna: Study problems and perspectives

The soil macrofauna, including animals between 1–2 mm and 20–30 mm in size, uses soil differently from the mesofauna, which lives in cavities, or microfauna that inhabits water films. In some ecosystems, the macrofauna accounts for most of the total soil animal biomass and substantially contributes to soil food-web functioning. Additionally, the macrofauna can be among the most diverse groups in the soil environment. A few macrofaunal taxa (e.g. earthworms and termites) are considered to be ecosystem engineers attracting research focus, while studies on most other soil macrofauna remain scattered and uneven. An analysis of 80 publications conducted for this study showed inconsistent definitions of soil macrofauna by specialists. Further, a comparison of taxa listed among the soil macrofauna and mesofauna deduced that researchers allocate soil animals to either group by higher-level taxonomic categories and not by size. The main challenge in soil macrofaunal surveys is the extremely high diversity of species from widely different taxa, which require highly specialised taxonomists to identify them to species level. The abovementioned publication analysis showed that small taxa, mainly insects, are often not surveyed. In addition, animals of the same species at different ontogenetic stages that coinhabit the soil are not analysed separately. This tendency leads to an underestimation of the abundance and biomass of early larval stages. Hence, the soil macrofauna is seldom included in analyses of soil ecosystem functioning and modelling. Synchronised and unified studies across biomes could draw more attention to this size group and increase research focus and output from soil ecologists and other scientists.