Estonian Academic Agricultural Society Agraarteadus 2228-4893 26 1 2015 6 20 Abundance and species richness of microannelids in humus cover of Estonian forest soils Mikroanneliidide arvukus ja liigirikkus Eesti metsamuldade huumuskattes 24 30 ET Raimo Kõlli Institute of Agricultural and Environmental Science, Estonian University of Life Sciences, Fr. R. Kreutzwaldi 5, 51014 Tartu, Estonia Ulfert Graefe IFAB Institute for Applied Soil Biology GmbH, Sodenkamp 62, 22337 Hamburg, Germany Indrek Tamm Institute of Agricultural and Environmental Science, Estonian University of Life Sciences, Fr. R. Kreutzwaldi 5, 51014 Tartu, Estonia The formation of humus profiles in forest ecosystems depends on the soil and plant cover types, and on the flux of falling debris into the soil. The transformation of "fresh organic matter" into humus is mainly performed by soil organisms. Therefore the species composition and abundance of living organisms in humus covers are good indicators in the evaluation of ecosystems functional efficiency and in understanding humus profile forming mechanisms. The abundance, species richness and vertical distribution of microannelids in the humus covers of forest ecosystems were studied in the pedo-ecological conditions of Estonia. The first research area (UA-I, Koorvere) is located in the pine forest of a Rhodococcum site type on a typical podzol with a sandy texture and fresh mor humus cover. UA-II (Kaagvere) is located in a mixed pine-spruce forest of Oxalis site type on a pseudopodzolic soil with a loamy sand on sandy loam texture and fresh moder humus cover. UA-III (Reola) – is in a spruce forest of an Oxalis drained swamp site type on a shallow fen soil with well decomposed peat and a eutrophic peaty humus cover. The mean abundance and species richness of microannelids in the humus covers of these three forest ecosystems (UA I-III) were respectively 17.0, 23.4 and 54.5 (in 103 individuals per m²), while the observed numbers of microannelids species were 1, 7 and 12. The highest number of one species per unit volume (319 individuals per one litre of soil) is characteristic of a moor type forest floor (UA-I) where, of the microannelids, only those in a strong acidity indicator group species Cognettia sphagnetorum were found. In the well decomposed eutrophic peat (UA-III) with the highest volume density (250 individuals L-1) the species found was Hemifridericia parva, which is an indicator of slight acidity, while in the moder type forest floor (UA-II) Enchytronia parva (177 individuals L-1) were found, which are an indicator of moderate acidity.