Distribution of ant species and mounds (Formica) in different-aged managed spruce stands in eastern Finland J. Kilpela ¨ inen 1 , P. Punttila 2 , L. Fine ´r 1 , P. Niemela ¨ 3 , T. Domisch 1 , M. F. Jurgensen 4 , S. Neuvonen 1 , M. Ohashi 5 , A. C. Risch 6 & L. Sundstro ¨m 7 1 Finnish Forest Research Institute, Joensuu Research Unit, Joensuu, Finland 2 Finnish Environment Institute, Research Department, Helsinki, Finland 3 Faculty of Forestry, University of Joensuu, Joensuu, Finland 4 Michigan Technological University, Ecosystem Science Center, School of Forest Resources and Environmental Science, Houghton, MI, USA 5 University of Hyogo, School of Human Science and Environment, Shinzaike-Honcho, Himeji City, Hyogo, Japan 6 Swiss Federal Institute for Forest, Snow and Landscape Research, Community Ecology/Animal Ecology, Birmensdorf, Switzerland 7 Department of Biological and Environmental Sciences, Ecology and Evolutionary Biology Unit, University of Helsinki, Helsinki, Finland Introduction Mound-building ant species are widespread in the boreal forests of Eurasia (e.g. Go ¨ sswald et al. 1965; Baroni Urbani and Collingwood 1977; Reznikova 2003). The wood ants of the Formica rufa group (Formica aquilonia Yarr., Formica polyctena Fo ¨ rst., F. rufa L., Formica lugubris Zett. and Formica pratensis Retz.) are common in Finnish boreal forests, but are most numerous in the medium-fertile and -dense Norway spruce- and birch-dominated mixed, mature stands of southern Finland (Wuorenrinne 1974; Keywords Formica rufa group, ant species turnover, boreal zone, forest succession, nest density, nest dimensions Correspondence J. Kilpela ¨ inen, Finnish Forest Research Institute, Joensuu Research Unit, PO Box 68, FI-80101 Joensuu, Finland. E-mail: jouni.kilpelainen@metla.fi Received: May 31, 2007; accepted: September 30, 2007. doi: 10.1111/j.1439-0418.2007.01244.x Abstract Mound-building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear-cut- ting can destroy wood ant colonies, and the species, abundance, dimen- sions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Fo ¨ rst., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well-lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well-lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concen- trated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment. J. Appl. Entomol. J. Appl. Entomol. 132 (2008) 315–325 ª 2008 The Authors Journal compilation ª 2008 Blackwell Verlag, Berlin 315