Invasive Exotics Impacts

Exotic invasive knotweeds (Fallopia spp.) negatively affect native plant and invertebrate assemblages in European riparian habitats.

Esther Gerber

Friday, October 17, 2008 - 1:30-2:00

Invasive plants can be expected to impose a significant impact on the native vegetation and their associated food webs, simply by occupying a large amount of space in invaded habitats. One concrete example are exotic knotweeds (Fallopia spp.), originating from Asia that are considered to be among the most aggressive invasive weeds in temperate terrestrial ecosystems both in Europe and in North America. We set out to assess whether plant species richness and invertebrate assemblages in European riparian habitats invaded by exotic knotweeds differed from those found in native grassland- or bush-dominated riparian habitats, which are both potentially threatened by knotweed invasion. Our findings suggest that riparian habitats invaded by knotweeds support lower numbers of plant species and lower overall abundance and morphospecies richness of invertebrates, compared to native grassland- dominated and bush-dominated habitats. Total invertebrate abundance and morphospecies richness in Fallopia-invaded riparian habitats were correlated with native plant species richness, suggesting that there is a link between the replacement of native plant species by exotic Fallopia species and the reduction in overall invertebrate abundance and morphospecies richness. Moreover, biomass of invertebrates sampled in grassland and bushdominated habitats was almost twice as high as that in Fallopia-invaded habitats. Large-scale invasion by exotic Fallopia species is therefore likely to seriously affect biodiversity and reduce the quality of riparian ecosystems for amphibians, reptiles, birds and mammals whose diets are largely composed of arthropods.

Keywords: INVASIVE PLANT, RIPARIAN ECOSYSTEMS, ECOSYSTEM IMPACT