The effects of invasive knotweed (Fallopia japonica) on invertebrate communities in western New York

Abstract

Japanese knotweed (Fallopia japonica [Houttuyn] Ranse-Decraene) is one of the most aggressive invasive plant species. It shades out and displaces native plants by forming thick, fast-growing thickets and may also affect invertebrate communities. By impacting invertebrate communities, knotweed can disrupt animals across the food web, causing declines in bird and frog populations. The goal of this study was to determine how Japanese knotweed impacts invertebrate communities, and if the degree and severity of knotweed impacts are seasonal. To try to capture as many types of invertebrates as possible, we used pitfall traps as well as designed a cost-effective window trap alternative using a painted plastic bottle. We placed fifteen pairs of pitfall and bottle insect traps in three seasons in invaded areas and nearby control areas across seven parks in western New York. Twenty-six different orders of invertebrates were collected. While some invertebrates, such as spiders and weevils, were negatively affected by knotweed across all seasons, for others the impacts of knotweed were seasonal. However, some invertebrates, such as springtails, were positively affected by knotweed in one or more seasons. We also found that Japanese knotweed consistently had strong negative effects on flying invertebrates, and very few effects on ground-dwelling ones. Our research demonstrates that it is important to consider both taxa and season when investigating the effects of an invasive species on an ecosystem.