-1 Impact of red deer Cervus elaphus grazing on bilberry Vaccinium myrtillus and composition of ground beetle (Coleoptera, Carabidae) assemblage CLAUDIA MELIS 1,* , ASTRID BUSET 1 , PER ARILD AARRESTAD 2 , ODDVAR HANSSEN 2 , ERLING L. MEISINGSET 3 , REIDAR ANDERSEN 1 , ARNE MOKSNES 1 and EIVIN RØSKAFT 1 1 Department of Biology, Norwegian University of Science and Technology, Realfagbygget, N-7491 Trondheim, Norway; 2 Norwegian Institute for Nature Research, Tungasletta-2, N-7485 Trondheim, Norway; 3 Norwegian Centre for Ecological Agriculture, Tingvoll gard, N-6630 Tingvoll, Norway; *Author for correspondence (e-mail: claudia.melis@bio.ntnu.no; phone: +47-73596285) Received 28 June 2004; accepted in revised form 31 January 2005 Key words: Boreal forest, Carabidae, Ecosystem engineer, Grazing, Norway, Red deer Abstract. We studied the role of red deer Cervus elaphus L. as ecosystem modifier in boreal forest (Tingvoll municipality, 62°52¢ N, 8°20¢ E, Norway), during early summer of 2001. The effect of grazing by red deer on ground beetles (Carabidae) abundance and diversity was investigated across a gradient of grazing pressures. We trapped ground beetles by pit-fall traps from three homoge- neous winter grazing areas (ungrazed, medium grazed, heavily grazed). Bilberry Vaccinium myrt- illus (the main winter food for red deer) was sampled and its dry weight was measured for the three locations. Gradient analyses showed that grazing by red deer affects carabid species composition. Grazing significantly affected the amount of bilberry, which correlated with species variation. According to our predictions, we found a higher abundance of carabids in the heavily grazed location, but the species richness and the diversity indices were similar for the three areas. This study shows that overall species composition is altered along a gradient as consequence of red deer winter grazing and that red deer act as ecosystem engineer, by reducing the bilberry heather which dominates the field layer in early summer. Introduction Jones et al. (1994) described the role that many animals play in the modifica- tion and maintenance of habitats by defining ‘ecosystem engineers’ as ‘organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials’. The animal feeding strategies and their physical alteration to the environment affect plant and animal community composition, which in turn alters the biogeochemical cycling of nutrients and ions in soils, sediments and water (Naiman 1988). Jones et al. (1997) suggested that the overall (i.e. at larger temporal and spatial scale) effect of physical ecosystem engineers will be to increase species richness and abundance. Several studies show that herbivorous mammals influence, by their foraging activity, both the habitat structure (e.g. Pastor et al. 1993; Kielland and Bryant Biodiversity and Conservation (2006) 15:2049–2059 Ó Springer 2006 DOI 10.1007/s10531-005-2005-8