Differential effects of American pokeweed (Phytolacca americana) invasion on ground-dwelling forest arthropods in southwest Germany

Non-native plants can have strong effects on the structure and functioning of ecosystems. Recently, the American pokeweed (Phytolacca americana), indigenous to east United States, has expanded its range in many regions all over the world. The species combines several traits that facilitate its invasiveness and its impact on ecosystems in its introduced range. The aim of this study was to analyse the effects of P. americana on multiple ground-dwelling arthropods by conducting a field survey in three forest sites in southwest Germany. Key findings were that P. americana invasion resulted in an altered arthropod community structure compared to native reference sites. Furthermore, the carabid species composition was influenced by the invasion, however this effect was dependent on the forest site. Contrasting effects of P. americana invasion on individual numbers of single ground-dwelling arthropod taxa were observed including positive (3 taxa), negative (1 taxa) and neutral effects (8 taxa). For 2 taxa (Carabidae and Formicidae) the effect of P. americana invasion was dependent on forest site. Reasons for the effects on the local fauna might be altered environmental conditions (reduced herbaceous plant cover) and biotic interactions. The study shows that P. americana induces shifts in the native faunal assemblages. Since responses depend on taxonomic groups and regions, the study highlights the importance for considering multiple taxonomic groups in evaluating the ecological impacts of invasive plants and that the evaluation of impacts must consider the regional context.