Reconsidering interspecific co-occurrence of native and invasive plants in an anthropogenic riparian ecosystem

Irene De La Forge, Amélie A.M. Cantarel, Christelle Boisselet, Emma Silvestre, Marylise Cottet, Florence PIOLA 

Invasive non-native plants are considered mostly though negative interactions, but are increasingly recognized as potential contributors to ecosystem functioning. By modifying microhabitats, resource availability and species interactions, non-natives plants may reshape and maintain the living conditions of native plant communities. We conducted an observational field study to quantify the interspecific relationships of coexistence between riparian herbaceous plants and three vegetation types: Fallopia x bohemica (invasive non-native), Rubus caesius (invasive native), and an uninvaded riparian forest (control). Seasonal monitoring of species richness was carried out over one year, combined with measurements of vegetation cover rate and functional traits relating to growth, flowering, and seed production in spring. Fallopia patches showed similar species richness, vegetation cover and functional traits compared to uninvaded areas in spring. In contrast, Rubus was associated with a lower number of co-occurring species and a reduction of growth and reproduction. Our findings demonstrate that Fallopia was associated with comparable plant richness and measured spring trait values under the uninvaded areas, and to a greater extent than Rubus. Rather than viewing non-native plants solely as threats, our example highlights the importance of adopting a more nuanced, context-dependent perspective that considers their potential to help maintain biodiversity in ecosystems subject to anthropogenic alterations.