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Taxon specific response of carabids (Coleoptera, Carabidae) and other soil invertebrate taxa on invasive plant Amorpha fruticosa in wetlands

False indigo (Amorpha fruticosa L.) is an invasive exotic plant introduced to Europe in the early 18th century. Its spread has been rapid, particularly in disturbed wetland habitats, where it forms dense impermeable monospecific stands and modifies habitat conditions. The impact of Amorpha fruticosa on native plant communities has been well analyzed, however knowledge concerning the possible effects on soil invertebrates and particularly carabid beetles is completely lacking. This study analyzed the impact of an Amorpha fruticosa invasion on carabid beetles and other soil invertebrates. Soil fauna was sampled by pitfall traps at natural habitats, initially colonized by Amorpha fruticosa, and habitats largely invaded by Amorpha fruticosa. In total 2, 613 carabid beetles belonging to 50 species and 72, 166 soil invertebrates were collected. The invasion of Amorpha fruticosa strongly affected the carabid beetle species composition, which clearly differed between all studied sites. Widespread euritopic carabid beetle species showed positive responses to Amorpha fruticosa invasion, while the activity density of open habitat species strongly declined. Mean individual biomass was significantly higher at invaded sites due to increased incidence of large carabids (genus Carabus Linné, 1758). Carabid beetle activity density and abundance of soil invertebrates were considerably higher at invaded sites than in natural sites. Conversely, the impact of Amorpha fruticosa on carabid beetle species richness and diversity was less pronounced, most likely due to immigration from adjacent habitats. Changes in carabid beetle species composition and abundance of soil invertebrates were most likely due to changes in vegetation structure and microclimate. The results suggest that Amorpha fruticosa invasion considerably affected carabid beetles, an insect group that is only indirectly related to plant composition. Therefore, severe future changes can be expected in invertebrate groups that are closely related to plant composition, since Amorpha fruticosa cannot be completely removed from the habitat and covers relatively large areas.

non-native plants; false indigo; diversity; microclimate; mean individual biomass

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