ORIGINAL PAPER Oribatid mite assemblages across the tree-line in western Norway and their representation in lake sediments Arguitxu de la Riva-Caballero • H. John B. Birks • Anne E. Bjune • Hilary H. Birks • Torstein Solhøy Received: 9 March 2009 / Accepted: 1 February 2010 / Published online: 23 February 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Little is known about the relationships between fossil oribatid mite assemblages in lake and mire sediments and the composition, abun- dance, and richness of their living communities. Because oribatid mites are a relatively new area of palaeolimnological study, there is a great lack of knowledge about the taphonomic processes that might affect fossil mite assemblages. The DOOR- MAT (Direct Observation Of Recent Macrofossils Across Tree-line) project was designed to study the transport and deposition of oribatid mites and plant remains in the tree-line area of western Norway. The present study also compares modern oribatid assemblages with fossil oribatid assemblages in a Holocene lake-sediment sequence from the nearby Trettetjørn, and considers the optimal location for studying fossil oribatid mites within a lake basin. Seven novel terrestrial traps (50 9 80 cm Astroturf doormats) were placed at major vegetational tran- sitions along an altitudinal transect crossing the tree-line ecotone from 633 to 1,120 m a.s.l. at Upsete, west Norway. Three sediment traps were placed in Trettetjørn (810 m a.sl.) at the inlet, the middle, and near the outlet. In each terrestrial trap, the oribatid assemblage was found to be character- istic of the surrounding habitat. The lake-trap analyses showed that aquatic or moist-habitat species had the highest chance of being incorpo- rated into the lake sediments; the number of terrestrial species decreased considerably from both outlet and inlet traps to the central trap in the deepest water. The area adjacent to the inlet of Trettetjørn would therefore be the optimal location for a sediment core for oribatid analysis. However, this conclusion is not supported when the modern trap results are compared with the Trettetjørn sequence from the lake centre. Keywords Acari Á Cryptostigmata Á Oribatida Á Humidity gradient Á Taphonomy Á Tree-line Electronic supplementary material The online version of this article (doi:10.1007/s10933-010-9411-y) contains supplementary material, which is available to authorized users. A. de la Riva-Caballero (&) Bergen Museum, University of Bergen, Thormølensgate 53a, 5007 Bergen, Norway e-mail: Arguitxu.caballero@bm.uib.no A. de la Riva-Caballero Á H. J. B. Birks Á H. H. Birks Á T. Solhøy Department of Biology, University of Bergen, Post box 7803, 5020 Bergen, Norway H. J. B. Birks Environmental Change Research Centre, Department of Geography, University College London, Gower Street, London WC1E 6BT, UK H. J. B. Birks Á A. E. Bjune Á H. H. Birks Bjerknes Centre for Climate Research, c/o Department of Biology, Alle ´gaten 41, 5007 Bergen, Norway 123 J Paleolimnol (2010) 44:361–374 DOI 10.1007/s10933-010-9411-y