Newsletter on Enchytraeidae 6: 59–67 (1999) 59 Indicator values, strategy types and life forms of terrestrial Enchytraeidae and other microannelids Ulfert GRAEFE 1 & Rüdiger M. SCHMELZ 2 Keywords: Ecological species classification, Oligochaeta, Annelida, soil biology, r- strategy, K-strategy, stress tolerance, humus form Abstract The ecological behaviour of soil microannelid species, mainly Enchytraeidae, is characterized, using the system of indicator values established for plants by Ellenberg (1992), and modifying it for annelids. The species are classified with respect to pH, soil moisture, salinity, reproductive strategy, stress tolerance, and their occurrence in the continuum of humus horizons and humus forms. The values given apply to the situation in Central Europe. Introduction The species assemblages of soil annelids exhibit considerable site-specific differences which can be used to describe and to characterize the ecological conditions of soil sites and which are suitable for a biological soil quality assessment (BEYLICH et al. 1995, DIDDEN et al. 1997, GRAEFE 1997). The site-specific differences of species assemblages reflect the peculiar and unique ecological behaviour of each species, which can be condensed, classified and expressed by values and numbers, as ELLENBERG et al. (1992) have done for plants. In this paper we present an ecological classification of a number of mesofaunal annelids, mainly Enchytraeidae, which have frequently been found in a large series of soil biological investigations in Central Europe, performed by the senior author, many of them in soil biomonitoring programs for German environmental agencies (GRAEFE et al. 1998). The values and numbers integrate ecological information about the species obtained from more than 1000 samples, including literature data (e.g. HEALY 1980). The species are classified according to the r-, K- and A-continuum (strategy types), according to their vertical distribution in the humus profile and their occurrence in the gradient of humus forms (life form types), and according to their behaviour towards the ecological factors pH, moisture and salinity (indicator value groups). The latter are chiefly inspired by ELLENBERG's indicator values for plants (ELLENBERG et al. 1992), whereas the life form types were elaborated especially for the soil mesofauna (GRAEFE & BELOTTI 1999). 1 IFAB Institut für Angewandte Bodenbiologie GmbH, Sodenkamp 62, D–22337 Hamburg 2 Universität Osnabrück, FB5, Spezielle Zoologie, D–49069 Osnabrück