Invasion by a non-native willow (Salix × rubens) in Brazilian subtropical highlands

Abstract

Human activities have been increasing pressure on riparian zones, affecting social benefits these ecosystems provide. Invasive species use river corridors as pathways to spread and consequently impact these ecosystems. Willows (Salix spp.) are important tree invaders worldwide. The invasiveness of Salix × rubens and its possible detrimental effects on Brazilian ecosystems have never been addressed. We hereby report the occurrence and invasion of S. × rubens in the highlands of southern Brazil, providing guidelines for the control of established populations and recommendations for safe cultivation to reduce invasions and environmental impacts. Through rapid field surveys and car-conducted roadside surveys performed in different seasons, S. × rubens individuals were located, counted and georeferenced. We registered 1929 individuals growing mainly along watercourses at altitudes between 826 and 1648 m above sea level. Our data provide evidence that S. × rubens has developed populations more than 100 m away from plantations in less than 50 years, likely facilitated by water transport, occasionally forming pure stands along rivers and floodplains. We concluded that S. × rubens is invading riparian ecosystems and thus must be acknowledged as an invasive species in Brazil.