Arthropod species richness in the Norway Spruce (Picea abies (L.) Karst.) canopy along an elevation gradient Juliane Ro ¨ der a,b, *, Claus Ba ¨ ssler b , Roland Brandl c , Libor Dvor ˇak d , Andreas Floren a , Martin M. Goßner e , Axel Gruppe f , Andrea Jarzabek-Mu ¨ ller b , Oldr ˇich Vojtech g , Christian Wagner b , Jo ¨rg Mu ¨ ller b a Department of Animal Ecology and Tropical Biology, Biocenter, Julius Maximilian University of Wu ¨rzburg, Am Hubland, D-97074 Wu ¨rzburg, Germany b Bavarian Forest National Park, Freyunger Str. 2, D-94481 Grafenau, Germany c Department of Ecology, Faculty of Biology, Philipps University of Marburg, Karl-von-Frisch-Str. 8, D-35032 Marburg, Germany d Municipal Museum Marianske Lazne, Goethovo Namesti 11, CZ-35301 Marianske La ´zne, Czech Republic e Institute of Ecology, Friedrich-Schiller-University, Domburger Str. 159, D-07743 Jena, Germany f Department of Animal Ecology, Center of Life and Food Sciences Weihenstephan, Technische Universita ¨t Mu ¨nchen, Hans-Carl-von-Carlowitz Platz 2, D-85354 Freising, Germany g S ˇ umava National Park Administration, Susicka 399, CZ-341 92 Kasˇperske ´ Hory, Czech Republic 1. Introduction Norway Spruce (Picea abies) is the most important forest tree species throughout Central Europe, including Germany (Schelhaas et al., 2003; BMELV, 2004). It was one of the comparably few tree species to survive the last glaciations in Europe, and spread from only four refugia: the Apennines, the Carparthians, the Dinaric Alps, and the area north of Moscow, Kostroma (Lagercrantz and Ryman, 1990; Giannini et al., 1991; Vendramin et al., 2000; Ravazzi, 2002). Although this natural colonization continues (Lagercrantz and Ryman, 1990), its recent contribution to the total cover of spruce can be neglected, considering the vast extension in range owing to planting campaigns over the last centuries (BMELV, 2004; Hosius et al., 2006)(Fig. 1). Favored by modern forestry as a fast-growing tree species with high growing stocks and valuable wood, spruce has been cultivated in large-scale plantations at lower elevations instead of the natural beech and oak trees, even far from its cooler montane and subalpine natural ranges (Walentowski et al., 2004). Following the definitions of Richardson et al. (2000), we can consider Norway Spruce at elevations outside its natural range, i.e., below 650 m a.s.l. (Walentowski et al., 2004), as a naturalized species in the Bohemian Forest and in colline parts of Central Europe. Outside of its natural range, the species is only found on plantations; it has not spread from the plantations or from areas of natural occurrence. Therefore, Norway Spruce cannot be considered as invasive. Norway Spruce is probably not able to establish viable populations on its own because it would be out-competed by European Beech (Fagus sylvatica (L.)) without human intervention. Forest Ecology and Management 259 (2010) 1513–1521 ARTICLE INFO Article history: Received 11 November 2009 Received in revised form 13 January 2010 Accepted 14 January 2010 Keywords: Temperature gradient Additive partitioning Conifer plantation Arthropod Host specialization Global warming ABSTRACT Norway Spruce is the economically most important tree species in Europe and has been cultivated in plantations on a large-scale at low elevations, far outside its natural range. In the Bohemian Forest, it naturally occurs in pure stands above 1150 m a.s.l. and as a mixed tree species from 650 to 1150 m a.s.l. An understanding of natural distributions and the diversity along temperature gradients at various elevations is important for conservation, pest management, and predictions of future species assemblages by global warming. Here we investigated the species richness of canopy arthropods in spruce trees along a gradient from 300 to 1300 m a.s.l. using flight-interception traps. We analyzed species richness by combining diversity partitioning with a moving window approach after standardizing sample size per plot. Total richness decreased linearly as the elevation increased, which reflected declining temperatures and a declining regional species pool. Phytophages (herbivores excluding xylophages) were the most influenced. Richness did not peak at the transition zones of the three ecological elevation zones, neither for all species, nor for any of the separate functional groups. However, the proportion of both beetle and true bug spruce specialists significantly increased with elevation and actually doubled in richness above 1000 m a.s.l., where spruce is naturally dominating. Our results indicate that even planted spruce trees at lower elevations maintain high levels of species richness. Further climate warming will promote overall species richness, especially of phytophages, at all elevations. However, spruce specialists may be seriously threatened by global warming. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author at: Bavarian Forest National Park, Freyunger Str. 2, D- 94481 Grafenau, Germany. Tel.: +49 8552 96 00 179. E-mail address: juliane.roeder@freenet.de (J. Ro ¨ der). Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco 0378-1127/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2010.01.027