High co-occurrence of invasive wetland plants and species at risk in Canada’s biodiverse Carolinian

Invasive species are a major driver of biodiversity loss, with invasive plants increasingly threatening wetland ecosystems. Southern Ontario’s Carolinian Zone, a biodiversity hotspot supporting 79% of Ontario’s non-fish Species at Risk (SAR), is especially vulnerable. Over half (54%) of these SAR rely on wetland or semiaquatic habitats, emphasizing the importance of wetland protection for their recovery. These habitats are fragmented and highly susceptible to plant invasions. To guide conservation, we conducted a spatial co-occurrence analysis of non-fish SAR dependent on wetlands and invasive wetland plant species. We identified 33 invasive species posing current (n = 26) or imminent (n = 7) threats in the Carolinian Zone. Overlap between SAR and invasive plants was greatest in Lake Erie’s coastal marshes and shallow waters, where invasions are well documented, and also in urban areas such as Toronto, Windsor, London, and Niagara, where SAR richness was unexpectedly high. Co-occurrence of SAR and invasive plants in these regions indicates that managing invasive plants in urban wetlands could directly support SAR recovery. Marsh-nesting birds, reptiles, and wetland plants were most exposed and vulnerable to habitat alteration and resource competition. Spatial analyses help pinpoint where invasive plants most threaten SAR, enabling targeted, effective management.