4th. European Conference on Biological Invasions
"Neobiota - From Ecology to Conservation" - Vienna, 27-29.9.2006 - p. 198
Impact of invasive exotic knotweeds (Fallopia spp) on invertebrate
communities
Gerber E, Schaffner U, Krebs C, Murrell C, (all CABI Switzerland Centre,
Switzerland), Moretti M WSL Swiss Federal Research Insitute, Switzerland
Exotic knotweeds (Fallopia spp) are considered to be among the most serious invasive
exotic weeds in Europe, causing significant damage to native ecosystems. However,
with the exception of competitive exclusion of native vegetation, their suggested
ecological impact is poorly supported by experimental studies.
In 2004, we started to investigate the ecological impact of exotic knotweed species in
selected areas of France, Germany and Switzerland. Specifically, we aim to assess their
effects on invertebrate community in natural and semi-natural habitats. Ten locations
were selected along river courses with different levels of knotweed infestations, and
pitfall traps and combi traps (to catch flying insects) randomly established in vegetation
invaded by exotic knotweed, as well as in vegetation which can potentially be invaded
by knotweed: open vegetation dominated by grasses and forbs, and bush-dominated
vegetation.
Results indicate that invasion by exotic knotweeds does not only have strong effects on
native vegetation, but also negatively affects invertebrate communities. The overall
abundance, biomass and diversity of invertebrates in plots invaded by exotic knotweed
were strongly reduced compared to control plots. Exotic plant species are in general
introduced without their specific natural enemies and are also often less palatable to
generalist herbivores. In accordance with this, we found reduced diversity for herbivore
invertebrates in knotweed patches. In addition, a negative effect of exotic knotweeds
could also be detected in other trophic groups (predators, detritivores). However, not all
invertebrate groups responded in the same way, and species number for ground beetles
was in fact highest in knotweed stands. Ground beetles might nevertheless be negatively
affected by these exotic plants as indicated by reduced size of Abax parallelepipedus
(Carabidae) individuals captured in knotweed, presumably resulting in a reduced fitness
of individuals.