Willow above, changes below: Seedless tree invader impacts riparian seed bank in the Patagonian ecotone

Aim: The soil seed bank, an ecosystem component with a crucial role in the naturalregeneration of plant communities, can be impacted by invasive non-nativeplants.The impact of non-nativeplants can be direct with the production of their own seedsor indirect without producing seeds, which has been less investigated. We determinedthe impact of an invasive seedless tree, non-nativewillow (Salix × rubens), on the soilseed bank in a riparian ecosystem.Location: Northwestern Patagonia, Argentina.Methods: In autumn and spring 2022, we collected soil samples and estimatedunderstorey cover, respectively, in plant communities invaded by willow and inuninvaded communities with a canopy dominated by native species. Over a year, werecorded the seedling emergence of soil samples to estimate the abundance, richness,and composition of the seed bank. We also compared the composition between theseed bank and understorey.Results: Total seed abundance and native woody species seed abundance decreasedtwofold and fourfold, respectively, in invaded plant communities in comparison withuninvaded communities. The most affected woody species was Ochetophila trinervis,a key tree species, because of its dominance in the canopy and understorey, and itsrole in various ecological processes (nitrogen cycling). In addition, willow invasionmoderately changed the seed bank species composition producing species turnover.For both the seed bank and the understorey, species composition was more similarbetween invaded and uninvaded communities than between the seed bank andunderstorey. Willow invasion had more impact on understorey composition than onthe seed bank.Conclusions: Although willows do not produce seeds regionally, their invasionnegatively impacts the soil seed bank by replacing native woody canopy species thatsupply seeds to the seed bank. These impacts could result in notable changes in thestructure of the plant communities and the ecosystem dynamics of riparian areas.