The pathways of introduction of alien cactus species to South Africa: lessons for risk assessment

The pathways of introduction of alien cactus species to South Africa: lessons for risk assessment
Ana Novoa1, David M. Richardson1, John R. Wilson1,2
1 Centre for Invasion Biology, Stellenbosch University; 2Invasive Species Programme, SANBI

The global pool of alien plant species is strongly shaped by trends in human trade and transport. Pathways, defined as a suite of processes that result in the introduction of an alien species from one geographical location to another, are starting to be considered as a powerful instrument of alien species management and biosecurity. In this study we examine the pathways of introduction of Cactaceae species (1846 species native to North and South America) into South Africa as an example. Scientific papers and grey literature were scrutinized, expert knowledge was consulted, and a survey of all businesses involved in the cactus trade in South Africa was performed. Our results show that until the 20th  century, the dominant pathway for cacti establishment in South Africa was deliberate planting done by farmers for economic reasons - for forage, fences or human consumption.

In recent times, horticulture has increased greatly in importance and is now the only pathway of introduction for new cacti species. We found 70 nurseries as well as supermarkets, unofficial markets, and small illegal retails involved in this trade. Despite this large commercial network, we found that all imports came from the same source. Many imported cacti were sold under incorrect scientific names, making effective regulation of the ornamental cactus industry in South Africa impossible. We ordered seeds of every imported species and variety. Seeds were germinated and DNA barcoding techniques were applied. We then compiled a precise list of imported cactus species. Finally, we developed a risk assessment protocol for the listed species with the purpose of informing policy and regulating the cactus trade. This study provides an interesting example of how complete and accurate listing information is a fundamental ingredient for an effective strategy for managing invasive alien species.