Multispecies invasion can reduce the impact of single alien plants
It is often considered that habitats invaded by multiple invasive non-native species may suffer greater negative impacts than habitats invaded by single species. Juglans regia (Juglandaceae) is native to parts of the EPPO region, but non-native to Central Europe. The species has invaded woodland and abandoned agricultural land in central Europe, often being dispersed via seed spread by birds. Solidago canadensis (Asteraceae: EPPO List of Invasive Alien Plants) is native to North America and has been shown to have negative impacts on native biodiversity in the EPPO region. Both species have been shown to have allelopathic effects on native plant species. The potential impact of the two species was studied on native vegetation in abandoned fields in Poland. Native plant species richness and native plant cover was assessed in six different vegetation types. In some sites, the presence of Betula pendula (Betulaceae) was used as a control as the species is native and has a tendency to become established in abandoned fields, but it is non-allelopathic. The sites included native vegetation and (1) B. pendula (2) J. regia, (3) S. canadensis (4) S. canadensis and B. pendula and (5) J. regia and S. canadensis. When S. canadensis invaded alone, it caused a larger decrease in species richness and cover (74%) than when J. regia invaded alone (58%). However, when J. regia and S. canadensis co‐occurred in abandoned fields, J. regia was dominant and strongly decreased S. canadensis density by 87%. The combined impact on native species diversity was much lower (15% decrease in native plant diversity) than when either S. canadensis or J. regia invaded alone.
Sources
Lenda M, Skόrka P, Knops J, Żmihorski M, Gaj R, Moroń D, Woyciechowski M, Tryjanowski P (2019) Multispecies invasion reduces the negative impact of single alien plant species on native flora. Biodiversity Research. DOI: 10.1111/ddi.12902