Community-level impacts of Amorpha fruticosa, Carpobrotus spp. and Lippia canescens in several Mediterranean coastal habitats of France
Amorpha fruticosa (Fabaceae, EPPO List of Invasive Alien Plants), Carpobrotus acinaciformis and C. edulis (Aizoaceae, EPPO List of IAP) and Lippia canescens (Verbenaceae) are invasive alien plants in the Mediterranean part of France. The community-level impacts of these species in several Mediterranean coastal habitats have been studied in France. Field work was therefore undertaken on these 3 species to assess their impacts on 2 Natura 2000 habitats for each of them, namely:
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Invasive alien plant
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Habitats
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Amorpha fruticosa
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Carpobrotus spp.
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Lippia canescens
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In each habitat, 3 sites were studied and within each site, 5 pairs of vegetation plots of 4 m² were sampled. Plots were chosen in both heavily invaded sites (where the invasive alien plant covered more than 80% of the vegetation) and in non-invaded sites with similar conditions (e.g. slope, exposure). Cover of all plants was then estimated on each plot. The changes in native species cover between invaded and non-invaded plots were then analyzed.
The magnitude of the impacts differed among the 3 invasive plant species, with Carpobrotus spp. exhibiting the largest impacts (-66% in species loss), and A. fruticosa showing no impact on the number of species present (+2%). The impact of Carpobrotus spp. in invaded sand dunes can be interpreted as a result of the important amount of litter it produces, which increases organic nitrogen therefore being detrimental to specialists of poor sandy conditions. A significant impact of Carpobrotus spp. has been detected on a regionally protected species (Euphorbia terracina, Euphorbiaceae), and on a regionally rare species (Silene nicaeensis, Caryophyllaceae).
Lippia canescens exhibited an intermediate effect on species loss, ranging from 11 to 26%. L. canescens clearly reduced the cover of dominant plants in salt meadows, indicating that this species also has an impact on agricultural activities by reducing available food for cattle.
Patches of A. fruticosa caused no significant loss in species richness. However, A. fruticosa had a drastic impact on characteristic species of grey dunes (Artemisia campestris subsp. glutinosa, Asteraceae; Helichrysum stoechas, Asteraceae) which were replaced by generalist ruderal species (Bromus sterilis, Poaceae; Carduus pycnocephalus, Asteraceae). This change could be related to nitrogen fixation due to root nodulation.
Sources
Chagué N ; Fried G (2011) Community-level impacts of three invasive alien plants in Mediterranean coastal habitats. In: Bohren C, Bertossa M, Schönenberger N, Rossinelli M, Conedera M. (ed) 3rd International Symposium of Environmental Weeds and Invasive Plants. Abstracts. October 2 to 7 2011. Monte Verità, Ascona, Switzerland.
Available from Internet
http://www.wsl.ch/epub/ewrs/authors/detail_EN?id=124;type=authors Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research WSL.