Responses of decomposer community to root-isolation and addition of slash

We studied the causal relationships between forest harvesting and the soil decomposer community focusing on suppression of energy inputs from trees to the soil through root-mycorrhizal network and increased energy input to th e soil in the form of slash left on site. We by hypothesised that both of t hese factors would affect the decomposer community, since the soil food web has been regarded as a system in which the amount of resources controls th e numbers of consumers. To study the importance of these factors without ch anges in microclimate, like in sunshine and shade, taking place in clear-fe lled areas, the experiment was performed in a mature spruce (Picea abies (L .) Karst.) forest. The experiment with factorial design included two factor s, isolation of the tree roots in the study plots from the surrounding soil and addition of slash. The isolation increased soil NH4 content and promot ed growth of herbs. It had no effect on the total microbial or bacterial bi omass, but the amount of soil fungi decreased by 40% and community structur e of bacteria changed in the isolated plots. At the level of microbivores, fungivorous micro arthropods (collembolans and oribatid mites) decreased in their numbers while bacterivorous. nematodes slightly increased. In additi on, the isolation increased the numbers of enchytraeids with a 2 year delay . No effects on decomposers by slash addition could be detected. The respon ses of decomposers to the isolation were similar to those observed earlier in clear-felled areas. It was concluded that, in short-term, elimination of root-mycorrhizal connections is one of most important factors affecting th e soil decomposer community after harvesting of northern coniferous forest. The effect of slash is, to a large extent, due to its effects on micro-cli mate and soil moisture. (C) 2001 Elsevier Science Ltd. All rights reserved.