The ecosystem resilience approach to control the invasive alien species Australian swamp stonecrop (Crassula helmsii)

The invasive Australian swamp stonecrop (Crassula helmsii) threatens species characteristic of shallow soft water lakes and pools, among others, in Europe. Anthropogenic disturbances, including restoration actions, of these ecosystems cause open niches in their littoral zones and allow C. helmsii to form dominant stands, especially under nutrient enrichment. Eradication of this invasive alien, amphibious, and clonal plant is, however, difficult and costly once a large population has established. For this reason, we here explore an ecosystem resilience approach (ERA) to control this invasive alien species. This approach includes suppressing the species by facilitating the occurrence and expansion of native vegetation. This requires a setback of C. helmsii's abundance by actively reducing its biomass, and the rehabilitation of optimal environmental conditions for native species. Our ERA study in four nature areas reveals that the introduction of native species makes the ecosystem more resilient against alien invasions, as shown by a lower abundance of this invasive plant species. Therefore, we state that ERA can effectively be applied in practice to decrease the invasibility of ecosystems by C. helmsii. Effectiveness, costs and benefits, and recommendations for application in practice are discussed. Overall, we argue that incorporating ERA in nature and water management will provide sustainable solutions in terms of biodiversity as well as more cost-effective applications for invasive alien species prevention and control.