Sensitivity of soil processes in northern forest soils: are management practices a threat?

Abstract

There is evidence that forest management practices influence soil-decomposer communities. It is also established that changes in the trophic structure and composition of these communities can induce changes in soil-nutrient dynamics, thereby affecting plant growth. Whether forest productivity is affected by management-induced changes in, e.g. soil faunal structure, is, however, yet to be shown. The aim of this study was (1) to determine the resolution of the ecological hierarchy (e.g. species, functional groups, trophic levels) at which a change in soil fauna would alter biotically-controlled processes in soils, and (2) to examine the sensitivity of soil fauna of the boreal forest floor to various kinds of forest management practices. A review of laboratory miniecosystem experiments carried out at the University of Jyväskylä is presented to examine the diversity-ecosystem function relationship. The response of tree growth to manipulation of soil-faunal composition was measured. A field experiment was conducted in central Finland in spruce stands, including several stand management treatments in addition to the untreated controls. The fellings took place in winter 1996, and various groups of soil animals have been sampled since 1995. Laboratory experiments revealed that soil processes and plant growth are largely insensitive to changes taking place at the species level of soil fauna. Some important keystone species may exist, but a change in the functional group architecture seems to be a prerequisite for altered rates in soil processes. Predators high up in the detrital food web had no detectable influence on any of the ecosystem-level processes. In the field, all of the faunal groups studied proved to be highly insensitive to the stand management practices. As compared to the untreated controls, numbers of enchytraeid worms, collembolans and most of the macroarthropods in the managed stands were not significantly different. It is concluded that management practices with minor impacts on the soil organic layer, which buffers soil biota against drastic changes in their environment, have little influence on biotically-controlled soil processes.