Killing it Softly: Girdling as an Efficient Eco-friendly Method to Locally Remove Invasive Acer negundo

Abstract

Acer negundo (boxelder maple) is a North American native tree species that currently invades riparian and disturbed areas in Europe, affecting both bank stability and ecosystem biodiversity. As a response to managers’ requests, we aimed at finding an eco-friendly method which would locally remove this species and help habitat restoration. Four control methods were tested on A. negundo adults and saplings from stands located in three experimental sites along different watercourses in Southwestern France: girdling, low cutting, high cutting, and cutting followed by the application of juglone (a natural allelopathic substance from walnut tree leaves). Mortality and resprout production on the treated A. negundo individuals were assessed during two years following the application of the control methods. Girdling was the most efficient method as it significantly induced higher mortality rates compared to the others (65 vs 15% of dead A. negundo two years after treatment administration). When healing emerged on trunks, yearly repeated girdling was required to reach full success. None of the control methods significantly reduced resprout production; not even the application of juglone. Girdling is the most recommended method to kill and remove A. negundo at a local scale in invaded natural habitats. Considering that A. negundo benefits from increases in light availability to outcompete native species, we further recommend removing seedlings from understories when applying girdling on adult and sapling individuals in order to optimize restoration conditions in natural stands and improve native species re-establishment.