Effects of an invasive plant on an endangered toad species

C. helmsii often invades the breeding habitat of endangered amphibians, such as Epidalea calamita. However, effects on natterjack population were unclear. The spawning rate, egg survival and the speed of larval growth of this toad species in relation to the presence of C. helmsii were studied. For this study we’ve measured temperature (by temperature data loggers) and chemical properties (by ICP- and AA analysis) of the water, as affected by C. helmsii. Additionally we’ve measured numbers of spawning, egg survival and larval sizes to investigate larval growth rate performing an exclosure experiment at a field location (Gijzenrooise zegge). *The data appropriate to this article may contain Dutch notes. For an English explanation, please contact the author of the data Abstract of the paper: The invasive Crassula helmsii is expanding in Europe. Several ecological effects are described, most of which focus on ecosystem functioning and native vegetation but rarely on fauna. In North-western Europe, C. helmsii often invades the breeding habitat of endangered amphibians, such as Epidalea calamita. The spawning rate, egg survival and the speed of larval growth of this toad species in relation to the presence of C. helmsii were studied. In order to unravel causal mechanisms, the outcome is related to temperature and chemical properties of the water, as affected by C. helmsii. Spawning and egg survival were significantly lower in case of C. helmsii dominance compared to bare soil conditions, and negatively affected the population size of E. calamita. However, larval growth rate was significantly higher in C. helmsii dominated treatments, which could be beneficial for tadpoles. Differences in water temperature and chemistry were a possible explanation for these effects. It remains unclear whether the population viability of E. calamita is negatively affected when C. helmsii is present. In many areas, however, this plant species completely overgrows and causes desiccation of waterbodies. Therefore, appropriate management measures will be required to protect this toad against this invader

Innovative control of C. helmsii

The invasive Australian swamp stonecrop (Crassula helmsii) threatens species characteristic of shallow soft water lakes and pools in Europe. Eradication of this plant is, however, difficult and costly once a large population has established. For this reason, we here explore a novel ecosystem resilience approach (ERA) to control this species. These datasets contain information about the first field performances of the ERA. Effectiveness of the ERA is measured by determining the cover (%) of the invasive species and the introduced and naturally established native vegetation after the introduction of a competing species in field plots. Additionally we’ve observed and measured field characteristics (soil- and water nutrient content by AA- and ICP analysis) to describe difference between the treated locations. *The data appropriate to this article may contain Dutch notes. For an English explanation, please contact the author of the data Abstract of paper: The invasive Australian swamp stonecrop (Crassula helmsii) threatens species characteristic of shallow soft water lakes and pools in Europe. Anthropogenic disturbances 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 amphibious and clonal plant is, however, difficult and costly once a large population has established. For this reason, we here explore a novel ecosystem resilience approach (ERA) to control this species. This approach includes supressing the species by facilitating the occurrence and expansion of native vegetation. This requires a set-back 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 shows that restoring abiotic conditions, a one-time reduction of C. helmsii’s biomass and the introduction of native species makes the ecosystem more resilient against invasions, as shown by less recolonization 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 more sustainable solutions in terms of biodiversity as well as economics for invasive species prevention and control

Reducing nutrient availability and enhancing biotic resistance limits settlement and growth of the invasive Australian swamp stonecrop (Crassula helmsii)

The Australian swamp stonecrop is invasive due to its efficient colonization of empty niches. The establishment of dense C. helmsii growth is threatening native biodiversity and functioning of freshwater ecosystems. In this study we’ve tested the competitive strength of C. helmsii in a greenhouse experiment with two native competitor species of the same habitat type, Pilularia globulifera and Littorella uniflora. After the collection of native vernation and bare soil sods we manually infested these with 60 propagules of C. helmsii. The settlement and growth of C. helmsii was assessed (by counting) after five weeks. In addition, the effect of nutrient enrichment by water bird feces on competition was studied by adding waterfowl droppings. Additionally we’ve measured nutrients in soil and water samples (by AA- and ICP analysis) collected from the sods. This gives insights in the establishment success and invasiveness of C. helmsii in absence of native competitors and eutrophication. *The data appropriate to this article may contain Dutch notes. For an English explanation, please contact the author of the data Abstract of the paper: The invasive Australian swamp stonecrop, Crassula helmsii, is a perennial amphibious herb originating from Australia and New Zealand. In freshwater wetlands of North-western Europe, this alien plant species is invasive due to its efficient colonization of empty niches. The establishment of dense C. helmsii growth is threatening native biodiversity and functioning of freshwater ecosystems, especially oligotrophic wetlands with high disturbance and nutrient enrichments. As the effects of these potential drivers of ecosystem degradation are generally difficult to determine in the field, we tested the competitive strength of C. helmsii in a greenhouse experiment with two native competitor species of the same habitat type, Pilularia globulifera and Littorella uniflora. Sods dominated by either of the native species, as well as bare soils, were collected from the field and manually infested with propagules of C. helmsii. Settlement and growth of C. helmsii was assessed after five weeks. In addition, the effect of nutrient enrichment by water bird feces on competition was studied by adding waterfowl droppings. C. helmsii was able to settle successfully in all treatments, but P. globulifera and L. uniflora dominance reduced settlement success and growth of C. helmsii. On vegetated sods, the addition of waterfowl droppings had a low effect on the performance of C. helmsii, however, this treatment significantly increased biomass production on bare soils with low nutrient availability. We conclude that both absence of native competitors and eutrophication, including guanotrophication by waterfowl, explain the establishment success and invasiveness of C. helmsii. Given the fact that eradication of C. helmsii is very challenging, our results imply that management should focus on a combination of increasing local species densities and abating eutrophication. This will strongly limit the window of opportunity for invasion of C. helmsii and enhance resistance by native plant communities