A pre-release assessment of the relationship between the invasive alien plant, Pereskiaaculeata Miller (Cactaceae), and native plant biodiversity in South Africa

The relationship between invasive alien plant densities and native plant biodiversity is poorly understood for most invasive plant species. Understanding this relationship can be useful in the development of management strategies and goals for biological control. In this study, the relationship between weed density and native plant biodiversity measured as species richness, Shannon H and Simpson’s D diversity were calculated for the invasive alien plant, Pereskiaaculeata Miller (Cactaceae), in South Africa. There was no significant difference in native plant biodiversity between P.aculeata densities of 50% and 100% but significantly higher native plant biodiversity was recorded at sites with P.aculeata densities of less than 50%. Maintaining P.aculeata densities of 40% and below is therefore an appropriate goal for biological control in terms of protection of native plant biodiversity. The ultimate goal for the biological control program should be to maintain P.aculeata at 30% density or lower because at these densities there was no significant difference in native plant biodiversity from if the weed were absent from the ecosystem.

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► The relationship between weed density and native plant biodiversity was calculated.
► Higher biodiversity was associated with weed densities of 50% and lower.
► At weed densities of 30% native biodiversity was not significantly different from 0%.
► Thirty percent and 50% weed densities are appropriate goals for biological control.