The most threatened cacti
Kew botanist Daniela Zappi is one of the authors of a paper highlighting the extinction risk faced by the charismatic cactus family, and is involved in helping the Brazilian government to improve the measures taken to protect cactus species.
UCN blanket assessment of cacti
Global species assessments, in which every extant species in a taxonomic group is systematically assessed, have been conducted only for very few plant groups such as cycads, conifers, mangroves and sea grasses (IUCN 2014, Polidoro et al., 2010, Short et al., 2011).
Cacti have a wide distribution in the Americas and a single epiphytic species that also reaches Africa and Asia. Apart from two poorly known species, Goettsch et al. (2015) have assessed all other 1,478 species recognised in the family (Hunt et al. 2006) in terms of their distribution and threats in a series of workshops focusing on the different centres of endemism and diversity (Mexico and US, Caribbean, Western South America and Brazil). These eight workshops were organised by Barbara Goettsch and involved cactus specialists from diverse countries, as well as mediators from IUCN who ensured that the assessments for each species were comparable, resulting in meaningful assessments. A typical workshop would address issues spanning species taxonomy, distribution, knowledge of the vegetation and particular threats to each population, as well as existent and potential risks, such as knowledge regarding illegal trade and future country developments (mining, agriculture, urbanisation).
The knowledge that plant species, and especially cacti, have on average smaller geographic range sizes than other living organisms (Gaston,2003) is particularly worrying because the distribution range is a key correlate of extinction risk. As a response to this concern, the Global Strategy for Plant Conservation (Joppa, 2013) has identified determining the threat status of all plant species as one of its key targets for 2020.
Given the charismatic Cactaceae are distributed predominantly in the New World arid lands (think cactus and cowboy), it is alarming that these sometimes desert environments have not attracted as much conservation attention as other Neotropical biomes such as the tropical forests (Durant, 2012).
The global Cactaceae assessment indicates that the extinction risk faced by cacti, with 31% of species placed either as Critically Endangered, Endangered or Vulnerable, is higher than found for most other plant groups assessed: proportions of threatened species vary between one in five and one in in four of all plant species (Brummitt et al., 2015). Our results indicate that negative human impact on arid lands is particularly high in the case of cacti and they also highlight the negative effect of illegal plant collecting on populations of ornamental plants.
Our study shows that the most affected areas, or the peaks of threatened cactus species richness are:
- a highly restricted area in southern Rio Grande do Sul, Brazil, and northern Artigas, Uruguay (area = c.500 km2) - this region also shows a peak in the proportion of species threatened with extinction;
- the Mexican states of Querétaro and San Luis Potosí, and in Oaxaca and Puebla in the Tehuacán-Cuicatlán region;
- Eastern Brazil, in eastern Bahia and northern Minas Gerais;
- Chile, in the southern portion of Antofagasta;
- Eastern Uruguay.
A comparison of species distribution area and the level of risk of the species has shown that the peaks of threatened species richness are very narrow in this family of plants, reflecting a fact that is known to cactus enthusiasts worldwide: that many cacti have particularly small geographic range sizes.
Brazilian Cactus Action Plan
Considering the finding that two of the top five areas where cacti are found within Brazil, and following on from years of specific research in cacti carried out at Kew (Taylor, 1991; Zappi, 1994; Taylor & Zappi, 2004; Hunt et al., 2006; Taylor, 2012), with a main focus on Brazilian species, the idea of preparing a national action plan for this family was put forward in 2010.
The resulting action plan (Ribeiro-Silva et al., 2011) is periodically reviewed and has engaged over 20 researchers and their teams to address the biology, cultivation and genetics of Brazilian cacti. Genetic studies (Bonatelli et al., 2014) are particularly important if we are to understand the variability of the species, especially when considering how much the appearance of cacti may be determined by the harsh environment where they occur (Menezes et al., 2015).
In terms of Brazilian cacti, the study of species from the southern states is particularly important, to promote their conservation. Most populations are small and isolated in rocky outcrops dispersed in the grassy Pampa biome, and the creation of large parks and reserves does not serve the purpose of protecting these small, isolated populations. One of the researchers, João Larocca, currently works with local land-owners in the creation of private reserves known in Brazil as Reservas Particulares do Patrimônio Natural (RPPNs). He has developed a management plan to take this work forward, but the biggest challenges are lack of funding and the fact that the plan has to take into account populations of cacti that occur across the border into Uruguay and Argentina.
Concerning the major Brazilian cactus diversity hotspot, Eastern Brazil (Taylor & Zappi, 2004), one of the major threats to the species comes from the fact that many of these occupy highly specific substrate. Iron ore -dwelling Arthrocereus glaziovii distribution around the city of Belo Horizonte has dwindled with massive exploitation of the iron rich substrate. In Bahia, Arrojadoa marylaniae, a critically endangered species, occurs strictly on pure quartzitic rock that is being currently surveyed for quarrying. Likewise, south of the border, in northern Minas Gerais, Coleocephalocereus purpureus grows solely over inselbergs of pink granite, a rock much appreciated by the building industry. The action plan highlights cases such as these, so that a response can be prepared by the governing bodies when an area is prospected for exploitation.
Bonatelli, I. A. et al. including Zappi, D.C. (2014). Interglacial microrefugia and diversification of a cactus species complex: phylogeography and palaeodistributional reconstructions for Pilosocereus aurisetus and allies. Mol Ecol. 23(12): 3044-3063. Available online
Brummitt, N. et al. (2015). Green Plants in the Red: A Baseline Global Assessment for the IUCN Sampled Red List Index for Plants. PLoS ONE 10(8): e0135152. Available online
Durant, S. M. et al. (2012). Forgotten Biodiversity in Desert Ecosystems. Science 336: 1379-1380. Available online
Gaston, K. J. (2003) The Structure and Dynamics of Geographic Ranges. Oxford University Press, Oxford.
Goettsch, B. et al. including Zappi, D. (2015). High proportion of cactus species threatened with extinction. Nature Plants 1: 15142. 10.1038/nplants.2015.142. Available online
Hunt, D., Taylor, N. P. & Charles, G. (2006). The New Cactus Lexicon. dh books, Milborne Port.
IUCN (2014). The IUCN Red List of Threatened Species. Version 2014.1. Available online
Joppa, L. N. et al. (2013). Achieving the Convention on Biological Diversity’s goals for plant conservation. Science 341: 1100-1103. Available online
Menezes, M.O.T. et al. including Zappi, D.C. (2015). Spines and ribs of Pilosocereus arrabidae (Lem.) Byles & G.D. Rowley and allies (Cactaceae): Ecologic or genetic traits? Flora - Morphology, Distribution, Funcional Ecology of Plants 214: 44-49. Available online
Polidoro, B. A., et al. (2010). The loss of species: Mangrove extinction risk and geographic areas of global concern. PLoS One e13636. doi: 10.1371/journal.pone.0010095. Available online
Ribeiro-Silva, S. et al. including Zappi, D.C. (2011). Plano de Ação Nacional para Conservação das Cactáceas. ICMBio, MMA, Brasília. Available online
Short, F. T. et al. (2011). Extinction risk assessment of the world’s seagrass species. Biol. Cons. 144: 1961–1971. Available online
Taylor, N. (1991). The genus Melocactus (Cactaceae) in Central and South America. Royal Botanic Gardens, Richmond, Surrey.
Taylor, N. (2012). Cacti and their habitats. Cactaceae Systematics Initiatives 28: 5–15.
Taylor, N. & Zappi, D. (2004). Cacti of Eastern Brazil. Royal Botanical Gardens, Kew, UK.
Zappi, D., (1994). Pilosocereus (Cactaceae): The genus in Brazil. Royal Botanical Gardens, Kew, UK.
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