Assessing the invasiveness of Berberis aristata and B. julianae (Berberidaceae) in South Africa: Management options and legal recommendations

• We examine the distributions, dynamics and invasion risks of Berberis aristata and B. julianae in South Africa.
• Both species are restricted to single naturalized populations and both have a moderate climatic suitability.
• Berberis aristata is a prime target for eradication, while B. julianae should be closely monitored.

The detection of two alien species spreading in natural ecosystems, namely Berberis julianae and Berberis aristata, prompted investigation into the risk that they pose as invasive plants to South Africa. Here we determined their distribution in South Africa, assessed population structure and reproductive size, determined seed germinability, evaluated the risks posed by the species by conducting weed risk assessments, and provide recommendations for control. We also assessed the extent of current and historic cultivation. B.julianae was found to be widely cultivated while but B. aristata was not found in cultivation. Only a single naturalized population was found for each species, with B. julianae occupying an area of 14 ha (0.02 ha condensed canopy) and B. aristata occupying an area 180 ha (1.58 ha condensed canopy). Given its very limited known distribution, there is an opportunity to eradicate B. aristata, although this would need to be reviewed if further surveys find new populations; we recommend that it be classified as category 1a invasive according to the National Environmental Management: Biodiversity Act. We do not yet recommend that B. julianae be regulated particularly given its horticultural popularity. However, it is clearly a species that needs to be monitored.