EFFECTS OF ORGANIC-MATTER REMOVAL ON THE SOIL FOOD-WEB - FORESTRY PRACTICES MEET ECOLOGICAL THEORY

We examine the long-term effects of removing forest harvesting residue s (above-ground whole-tree harvesting; WTH) in the soil food web, usin g data from two different experiments on slash removal and addition in Sweden. Removal of harvesting residues had negative effects on the ab undances of animals at higher trophic positions and on more mobile ani mals. Predators such as gamasid mites, spiders and staphyliniid and ca ntharid beetles decreased by 30-50% after WTH at both sites. Microbide tritivorous dipterans and fungivorous Collembola decreased at the pine site, but not at the more productive spruce site. Enchytraeids and ne matodes were usually not affected by WTH. No differences in fungal and bacterial biomass were found. The removal of organic matter had fairl y long-term, of the order of decades, effects on the soil food web. Th e effects were quantitative rather than qualitative. No functional gro ups disappeared after WTH. Our findings do not support the hypothesis that soil food webs are entirely donor-controlled. The more pronounced effects of WTH at higher trophic positions indicates that the major i nteractions in the food webs we have studied are reciprocal, i.e., tha t consumers to some degree control the density of their resources. (C) 1998 Elsevier Science B.V.