Reducing nutrient availability and enhancing biotic resistance limits settlement and growth of the invasive Australian s
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ORIGINAL PAPER
Reducing nutrient availability and enhancing biotic resistance limits settlement and growth of the invasive Australian swamp stonecrop (Crassula helmsii) Janneke M. M. van der Loop . Janne Tjampens . Joost J. Vogels Hein H. van Kleef . Leon P. M. Lamers . Rob S. E. W. Leuven
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Received: 15 February 2020 / Accepted: 29 July 2020 Ó The Author(s) 2020
Abstract 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
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10530-020-02327-0) contains supplementary material, which is available to authorized users. J. M. M. van der Loop (&) J. J. Vogels L. P. M. Lamers R. S. E. W. Leuven Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands e-mail: [email protected] J. J. Vogels e-mail: [email protected]
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 J. M. M. van der Loop H. H. van Kleef L. P. M. Lamers R. S. E. W. Leuven Netherlands Centre of Expertise on Exotic Species (NECE), Toernooiveld 1, 6525 ED Nijmegen, The Netherlands J. Tjampens Flemish Land Agency (VLM), 3000 Louvain, Belgium e-mail: [email protected]
L. P. M. Lamers e-mail: [email protected] R. S. E. W. Leuven e-mail: [email protected] J. M. M. van der Loop J. J. Vogels H. H. van Kleef Stichting Bargerveen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands e-mail: [email protected]
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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
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