The Conservation Of Cacti And Succulents In Botanic Gardens
Volume 7 Number 1 - January 2010
Sara Oldfield and David Hunt
Botanic gardens have an important role to play in ensuring that no species of cactus or other succulent plant becomes needlessly extinct
Botanic gardens around the world have impressive collections of cacti and other succulents for display, landscaping, research and education purposes. With a significant proportion of arid land plant species being threatened with extinction in the wild, the living collections in botanic gardens also have huge potential for ex situ conservation and restoration of natural populations. Some botanic gardens are already using their collections to fulfil these important roles. Individual gardens can use the BGCI PlantSearch database to check the conservation status of cacti in their collections. At a global level the PlantSearch Database can be used to analyse the extent to which threatened cacti and other succulents are in ex situ collections and to assist in planning for the long term conservation of these popular and charismatic plant species. BGCI has recently begun working with the International Organisation for Succulent Plant Studies (IOS) to evaluate collections of cacti for conservation purposes both in botanic gardens and in private collections.
The Cactaceae family has over 1,400 species and 380 heterotypic subspecies almost confined to the Americas. Mexico is the centre of diversity for the family with nearly 600 species and 170 heterotypic subspecies within the country. Threats to the species in the wild include over-collection for international commerce, the all too familiar processes of habitat degradation and destruction and the overarching problem of global climate change. A full Red List assessment for the family is currently being carried out coordinated by Dr Barbara Goettsch at University of Sheffield, UK in collaboration with the IUCN/SSC Cactus and Succulent Specialist Group, the Center for Applied Biodiversity Science at Conservation International (CI/CABS) and BGCI. As an interim measure, a preliminary assessment of the conservation status of cacti published in 2006 suggests that 542 species and subspecies are threatened with extinction (equivalent to CR, EN, VU) at a global scale (Taylor et al, 2006). Using this preliminary list an analysis of cactus holdings in botanic gardens has been undertaken using the PlantSearch Database. According to this survey, 366 of the globally threatened taxa are recorded in botanic garden collections.
“The Cactaceae are almost entirely endemic to the Americas; from British Columbia and Alberta in Canada, to Patagonia in Argentina”
Botanic garden collections
The most commonly recorded globally threatened cactus in botanic garden collections is Echinocactus grusonii. This distinctive species, now widely cultivated, was first discovered in 1889. Large numbers of wild plants were exported from Mexico and by the end of the 19th century there were fears about the potential extinction of the species. Unfortunately in 1995, the original habitat of the golden barrel cactus was destroyed by the construction of a dam in the Moctezuma River Canyon between the states of Querétaro and Hidalgo. Twenty years later, a new disjunct population of this species was discovered about 500 km away in the state of Zacatecas. The DNA structure of the plants from the new and original locations is currently being studied by researchers from the Universidad Autónoma de Querétaro, University of Reading, and the National Autonomous University of Mexico. Echinocactus grusonii is listed as Critically Endangered by Taylor et al, 2006. Over 130 botanic gardens have this species in their collections, according to BGCI’s PlantSearch database. For ex situ conservation purposes, plants of known wild origin are, of course, particularly valuable as they form part of the original gene pool of the species and have potential for re-establishment of populations close to their original localities.
Other globally threatened cacti that are held by a wide range of botanic gardens include the Mexican CITES Appendix I listed species, Ariocarpus trigonus, Aztekium ritteri, Obregonia denegrii and Turbinicarpus pseudomacrochele and Mammillaria spp such as M. plumosa, M. microhelia, M. magnifica, M. wiesingeri, and M. zeilmanniana. All of these are represented in over 30 botanic gardens as recorded in the PlantSearch database.
“Cacti have long been regarded as one of the most highly threatened plant families.”
In contrast, numerous globally threatened cacti including the Critically Endangered species, listed in Table 1, are not yet recorded in ex situ collections and BGCI is keen to hear from botanic gardens that might have these species in cultivation. It is clearly important that the world’s rarest cacti species are established as genetically representative and well-documented living collections as an insurance policy against extinction in the wild. In line with Target 8 of the GSPC, ex situ collections should preferably be in the country of origin. For cacti however there is a global responsibility to conserve the species that have been cultivated around the world for over one hundred years. Curation of collections valuable for conservation purposes needs to be carried out with particular rigour.
Table 1 Critically endangered cacti not currently recorded in the PlantSearch Database
In botanic gardens as in private collections, specialist skills and a keen interest in the species and their requirements will benefit the long term maintenance of cacti in cultivation. The IOS, with a membership of individuals working in botanic gardens and/or with private collections, has promoted conservation of cacti and other succulents for nearly 40 years. In 1980 the IOS published a Register of Succulent Collections with 73 collections included, 33 of which were at botanic gardens that are now BGCI members. Under the new IOS/BGCI collaboration we intend to assist collection holders in assessing and recognizing the resource value of individual plants in their collections, promote good practice in the documentation and secure labeling of plants, promote collaboration between collection holders in selecting groups to be treated as ‘specialities’ or as back-up collections, and assist collection holders with plant identification or verification via contacts with IOS experts.
The next stage in the IOS/BGCI collaboration will be to contact specialist cactus collections to seek information on the current status of plants maintained and to seek further collaboration. The intention is to maintain a shared record of the conservation value of collections based on factors such as accession policy, rarity of species in the wild and in cultivation, access to the material and willingness to collaborate and exchange propagation material. The need to reflect both the letter and the spirit of international agreements through CBD and CITES will be respected at all times.
“68% of threatened cacti are recorded in botanic garden collections”
A joint meeting will be held at the 31st IOS Congress being organized in collaboration with the Jardin Botanico “Viera y Clavijo” in Gran Canaria. This will consider how best to ensure that all globally threatened cacti are conserved with links between ex situ and in situ conservation. There are some good practical examples to draw on. In Mexico for example, with BGCI support, the Jardín Botánico Regional de Cadereyta “Ing. Manuel González de Cosío”, Querétaro, carried out a very successful project conserving threatened cacti with the participation of local communities - the species involved were Astrophytum ornatum, Echinocactus grusonii, Echinocereus schmollii, Mammillaria herrerae and Thelocactus hastifer. The project involved establishment of a community nursery to propagate the species which have been threatened by commercial collectors in the region.
Botanic gardens have an important role to play in ensuring that no species of cactus or other succulent plant becomes needlessly extinct. Working with the expertise available through IOS will enhance that role. At a practical level it remains a priority to develop more projects to support conservation of cacti in their natural habitats as far as possible involving local people as custodians of their flora. Ex situ collections indirectly support such activities, allowing for research into propagation techniques, provision of propagules for restoration and long term storage of living material and seeds. Raising awareness of the diversity and conservation needs of cacti is another important role for botanic gardens to play.
Oldfield, S. (comp.) 1997. Cactus and Succulent Plants – Status survey and conservation action plan. IUCN/SSC Cactus and Succulent Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK.
Taylor, N., Charles, G. and Lowry, M. 2006. Conservation assessments. In: Hunt, D. 2006. The New Cactus Lexicon. dh books, Milborne Port, England.