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Epigaeic arthropods were studied in intermediate-aged pure plantations of the exotic American Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and of European sessile oak (Quercus petraea Liebl.), which had both been established after forest clear-cuts. Studies took place in two blocks in a forest in northwestern Lower Saxony, Germany. Pitfall trapping throughout the vegetation period of 2004 delivered quantitative data for epigaeic macro-arthropods. Communities of ants (Formicidae), ground beetles (Coleoptera: Carabidae) and spiders (Araneae) were studied in further detail. Several differences in catch numbers, species richness and structure of communities became obvious between the studied stands and are partially interpreted as effects of the different tree cover. As far as environmental factors are concerned, the studied Douglas fir stands showed a high cover of mosses and needle litter, a low weed cover, and a higher soil acidity as compared to the sessile oak plantations. Activity of isopods and diplopods was significantly higher within Douglas fir stands than in those of sessile oak, whereas activity of ants, carabids and weevils was lower in the plantations of this exotic tree species. For all three taxa studied in detail, the numbers of exclusively recorded species were higher in oak stands. Except for wolf spiders (Lycosidae), spider communities of sessile oak sustained to a certain degree in the Douglas fir plantations. On the other hand, communities of ants and carabids were quantitatively impoverished under Douglas fir. Overall, non-metric multidimensional scaling (NMDS) and cluster analysis showed that the communities of all three taxa in focus were strongly altered by treatment and by area, with treatment prevailing over area. Furthermore, we expected especially carabid communities to recruit individuals continuously from the surrounding deciduous forests. With some reservations resulting from the few replicates studied we conclude, that (1) intermediate-aged pure Douglas fir plantations are no biodiversity deserts as a broad spectrum of epigaeic arthropods persists in the plantations, at least, when these are small.-sized. Furthermore, we conclude that (2) afforestation with exotic Douglas fir leads to conspicuous changes in epigaeic invertebrate communities as compared to autochthonous, deciduous forests of the same age class. Recommendations for forestry using Douglas fir and aimed at conserving biodiversity include the restriction of Douglas fir to recent and new forests, to avoid pure and dense stands, as well as to limit the total area stocked. (C) 2007 Elsevier B.V. All rights reserved.