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Abstract  Giant knotweeds (Reynoutria spp.) are highly productive and aggressive invaders in riparian wetlands of Europe and North America. We sampled ground-dwelling beetles by pitfall traps from six sites comparing monotypic Reynoutria stands with the invaded native Urtica-dominated stands. Three sites were located in a semi-natural softwood forest and three sites were on a ruderal embankment. The analyses are based on a total of 13,244 individuals from 218 species. Location and site significantly influenced beetle assemblages. Moreover, there were pronounced differences between vegetation stands. The monotypic Reynoutria stands exhibited lower beetle abundance, species richness and rarefaction diversity irrespective of location. However, the negative effect on species richness, abundance and assemblage similarities were stronger on the transformed ruderal embankment than in the semi-natural softwood forest. Reynoutria invasion seems to influence microclimatic conditions. We found a higher abundance of silvicolous and a lower abundance of xerophilous ground beetles in the Reyountria stands than in the Urtica-dominated stands. Feeding guilds reacted differently to Reynoutria invasion that reduced the abundance of predators and herbivores but enhanced that of detritivores. Detritivores assumingly profit from the perennial presence of the large quantities of Reynoutria litter. We conclude that highly productive invaders pauperise the arthropod fauna and alter link strengths in trophic cascades shifting primary producer-based food webs to detritus-based food webs. [ABSTRACT FROM AUTHOR]

We studied Coleoptera emerging from deadwood in a broadleaved forest that has been managed with nature-oriented forestry since 1990 and in which an accumulation of 10 m3 deadwood/ha has been achieved. We sampled a total of 11 m3 of deadwood from oak and beech trees and yielded 32,477 individuals pertaining to 342 species. The number of species emerging from oak deadwood was significantly higher than that from beech. Significantly more species emerged from deadwood with medium size (15–21 cm) diameter than from smaller (5–7 cm) or larger (40–60 cm) diameters. The stage of decay did not influence the number of species during the first 6 years of decomposition. Species richness strongly increased with the amount of deadwood sampled. Species–area regressions yielded z-values of 0.81 for oak and 0.87 for beech deadwood. The beetle assemblage was characterized by a low number of xylophagous species and a high number of mobile zoophagous species. However, two-thirds of the individuals sampled pertained to nine species of Scolytidae. This is why Shannon–Wiener diversity (H) and evenness-indices (E) greatly decreased with increasing number of scolytids. The species and individuals yielded from the sun-exposed deadwood outnumbered those from shaded areas. Namely the scolytid Taphrorychus bicolor reached remarkably high densities in the sun-exposed beech deadwood (>800 individuals/m2). In contrast, oak deadwood never harboured such high numbers of scolytids. Felling of moribund trees had decreased the number of scolytids but it had also considerably reduced the number of rare and endangered species. [ABSTRACT FROM AUTHOR]