Effects of Japanese Knotweed on avian diversity and function in riparian habitats

Abstract

The impacts of the invasive plant Japanese Knotweed (Fallopia japonica) on native plant and invertebrate communities in its introduced range have been relatively well studied, and studies have revealed predominantly negative impacts. However, little research has focused on the impact of knotweed on higher trophic levels. This study investigated how riparian bird communities respond to different levels of knotweed invasion. Birds were counted in 21 fixed-width transects located along ten streams in Pennsylvania, a prime avian breeding area, winter roosting site, and migratory staging area located along the Atlantic Migratory Flyway. Species richness and overall abundances did not significantly differ between levels of knotweed coverage. However, three species exhibited significant positive correlations with knotweed cover, and one species exhibited a significant negative correlation. Species and foraging guild composition differed between survey locations with and without knotweed. Species frequently found around human habitation and in degraded habitats were associated with knotweed, while more sensitive species were associated with native vegetation. Locations with knotweed were also associated with fewer foraging guilds and lacked an association with shoreline gleaners, water ambushers, and ground foragers, indicating a potential loss of ecological function. Given the widespread distribution of Japanese Knotweed, management actions to reduce or eliminate knotweed from riparian corridors are necessary in order to preserve avian diversity and function.