The impacts of Asian knotweeds on the environment and infrastructures

Abstract

"Knotweed is voracious and shows no mercy to its fellow plants. Its roots secrete substances that kill the roots of neighbouring plants. [...] the density of its leaves prevents the development of the other plants because of a lack of light. In short, a true serial killer plant!". This excerpt from an article in the newspaper Le Progrès (Lyon, 10 September 2016), accurately summarizes the public's perception of Asian knotweeds such as Japanese knotweed (Reynoutria japonica). It is not surprising that in Europe and North America, control measures against these plants are multiplying. However, is this perception based on facts? Are Asian knotweeds as harmful to the environment and public and private infrastructures as one would suspect by simply looking at the stands formed by these plants? This article details the results of an exhaustive scientific literature review on the impacts of knotweeds on the flora, fauna, soils and housing infrastructure. It shows that while some perceptions are probably true, particularly with regard to the impact of knotweed on the flora, others are based on fragile hypotheses not supported by science. The knowledge gaps are still very broad.