Functional implications of soil fauna diversity in boreal forests

This paper is a review of recent experiments dealing with the role of soil fauna in decomposition, mineralisation and primary production in coniferous forest soils. The experiments have been grouped according to the degree an d nature of the 'diversity gradient' between the 'more diverse' community a nd its control: single animal species or an uncontrolled mixture of species versus microbiota only, several known animal species of the same trophic g roup versus one species only (species diversity), two or more functional gr oups versus one only, and food chains with predators versus microbes and mi crobivores only. The evidence available at present suggests that taxonomic diversity and predation have no consistent effects on the process rates in soil, while adding to the 'functional' or 'trophic group diversity' results in a more predictable enhancement in mineralisation. Especially the enchyt raeid Cognettia sphagnetorum seems to be a keystone species in boreal fores t soils. However, there are only few experiments in which species diversity per se has been taken as a separate factor, without a simultaneous change in the number of trophic groups or in total decomposer biomass. (C) 1998 El sevier Science B.V.