Understanding willow invasion in subtropical highlands

Abstract

Willows invade many riparian environments around the world. Understanding the environmental factors that affect the establishment of non-native invasive plants, as well as characterizing population structure and stages of invasion, are crucial steps to define priority areas for monitoring and management. In this study, we characterized the population structure of the hybrid invasive tree Salix × rubens, determined the stage of the invasion process, and identified relevant factors for the establishment of regenerating plants in a subtropical riparian system in southern Brazil. We assessed population structure by measuring stem perimeter and height of plants sampled along river banks and riverbeds along several rivers, and measured environmental variables that may explain abundance patterns of regenerants. We showed that the majority of regenerants developed in riverbeds. The species seems to be transitioning between the establishment and dispersal phases of the invasion process. The abundance of regenerants was affected mainly by the abundance of nearby S. × rubens adults. Abundance of regenerants was negatively influenced by canopy openness, an unexpected result since S. × rubens is considered light-demanding. Our study provides insights for management strategies of S. × rubens, which must focus on searching sites along rivers where adult trees are present.