The Global Cactus Assessment (GCA) is evaluating the conservation status of the world’s cacti. The project is based in the Department of Animal and Plant Sciences at the University of Sheffield and works in collaboration with the IUCN/SSC – CI/CABS Biodiversity Assessment Unit and the Cactus and Succulent Specialist Group (CSSG). The principal aim of the project is to provide basic information on the species to facilitate conservation action. The project began in May 2008 and involves a network of collaborators who help compile existing data on the estimated 1438 known cactus species.
For the last five decades the IUCN through its SSC has been expanding and updating the Red List of Endangered Species, highlighting those threatened with extinction and promoting their conservation. The GCA will contribute to the SSC commitment to provide the world with the most objective, scientifically-based information on the current status of global biodiversity.
The plant family Cactaceae has approximately 1,500 species, and is almost entirely endemic to the Americas, being distributed from British Columbia and Alberta in Canada, to Patagonia in Argentina. It reaches its highest diversity in arid and semi-arid regions, and has its main centre of diversification in Mexico and the immediately adjacent south-western United States. The second most diverse region for cacti is the central Andes, comprising the countries of Peru, Bolivia, southern Ecuador, north-east Chile, and north-west Argentina. Other hotspots include eastern Brazil, central-western & southern Brazil, Paraguay, Uruguay and Argentina, and the Caribbean region.
One of the most striking features of cacti is their high levels of endemism at both generic and species levels. Brazil and Mexico have the highest levels of generic endemism, at 40% and 30% respectively. Astoundingly, however, 80% of all cacti occurring in Chile, 78% in Mexico, and 74% of Brazilian species are found within these respective countries and nowhere else in the world. Indeed, many species are known from areas covering only a few square kilometres.
As is the case for much of biodiversity, cacti are in a prickly situation. In fact, they have long been regarded as one of the most highly threatened plant families. The most significant anthropogenic pressures are agricultural development, mining, overgrazing and illegal trade. That cactus species are slow-growing, highly vulnerable to disturbance in their early stages, and have low recruitment rates, often makes the recovery of populations extremely difficult. Recent climate change projections suggest that in many regions this will pose an additional pressure; the North American Southwest will turn more arid, challenging the adaptation capabilities of cacti to more drastic droughts.
To date the threat status of only 157 (11%) of all cacti species has been assessed using the 1994 IUCN criteria. However, of these, 111 species are categorised as under a high risk of extinction in the near future.