Direct and indirect interactions promote the accumulation of nonnative plants after invasive species removal

TORRES, AGOSTINA; RODRÍGUEZ-CABAL, MARIANO A; NUÑEZ, MARTÍN A

Simposio; International Association for Vegetation Science (IAVS) 63rd Annual Symposium; 2021

International Association for Vegetation Science

Multiple nonnative species co-occur in most ecosystems, and understanding their interaction can be fundamental to explain nonnative invasion success and guide management strategies. Co-occurring invaders can facilitate each other leading to the accumulation of nonnative species in communities or they can compete with each other hindering further invasions. Interactions among nonnatives can be highly dynamic as their strength and even sign is affected by the environmental context in which they occur. In this context, the experimental removal of invasive species can be an important tool to help quantify the sign and strength of nonnative interactions while providing insights into the reassembly of multiple-invaded communities. To quantify nonnative interactions and their consequences on community assembly, we evaluated the community reassembly after selective removals of two highly invasive plant species, the sweetbriar rose (Rosa rubiginosa) and the scotch broom (Cytisus scoparius) (both target species), at two different times ? early and late removal - in field communities in Isla Victoria, Patagonia, Argentina. Target species showed negative asymmetric interactions that were dependent on the temporal context. While the scotch broom benefited from the sweetbriar rose?s early removal, the performance of the sweetbriar rose was independent of the abundance of the scotch broom. Removal of both target species resulted in communities with a higher abundance of nonnative species. Rose removal negatively affected native species, likely mediated by the release of the broom from competition. This suggests an indirect interaction between the rose and native species. In contrast, removal of the broom had a direct positive effect on nonnatives, which increased their representation in the community, an effect that was stronger during early removals. Overall, our results suggest that both direct and indirect interactions among plant species underlie multiple-invaded reassembly trajectories either by hindering native species performance or by specifically promoting nonnative species. Understanding the nonnative interaction network and its temporal dynamics can be an important tool to design management strategies aimed at reducing the accumulation of nonnative species.