IN THE CHIHUAHUAN DESERT CONSERVATION OF CACTI OF NORTHERN MEXICO

Over the last decade, a team of Mexican botanists have been studying the floristics, and biogeography of the many that grow in the Chihuahuan Desert. They have revealed the pattern of diversity and distribution of these to a level of detail rarely dry, inter-montane valleys, canyons and achieved but vital for conservation. HÉCTOR M. depressions that contain an important part of the region’s biodiversity; these desert HERNÁNDEZ, leader of the team, reports on the research fragments are home of a considerable undertaken and how it has provided vital tools for conservation. number of cactus species and even contain endemic genera, of which Aztekium, Geohintonia and Obregonia are examples.

ore than half of Mexico is arid The hottest, driest and lowest areas of and semi-arid. There are three this desert are in the Rio Grande and Mmain desert regions in Mexico Trans-Pecos regions of Texas (600 m ele- – the Chihuahuan Desert, the Sonoran vation at the valley bottom), in the Desert and the Tehuacán Valley – each Bolsón de Cuatro Ciénegas, Coahuila of which is distinctive but in different (740 m), and in the Bolsón de Mapimí, ways. In these regions, plants and ani- Durango (1075 m). As elevation increases mals have undergone a profound evolu- so too does the rainfall. The northern- tionary process, which has led to a wide most areas receive some snow during the variety of specialized life forms adapted winter months but, as the elevation to desert conditions. decreases and as one moves south, average temperatures rise and the seasons without With an estimated flora of 3,000 species frost become longer. and an interesting assemblage of animals, the Chihuahuan Desert in northern An amazing diversity of cacti Mexico is one of the most extraordinary I.dumortieri H-2420 deserts in the world. The region is bor- The cactus family (Cactaceae) occurs dered by two large mountain ranges, the throughout the Americas, mainly in dry Caption . . . ? Sierra Madre Occidental and the Sierra or highly seasonal regions in Mexico, Madre Oriental. Some half a million km2 southern United States, eastern Brazil, Mammilleria pottsil in size, it is the largest desert in North and parts of Bolivia, Peru and Argentina. Caption . . . Top:C-1375 America, extending from central Mexico It comprises about 100 genera and 1500 engelmannii north into parts of southeastern Arizona, species worldwide. Its highest diversity is C-191 N conoidea and southern New Mexico and Texas. in Mexico, where about 50 genera and Adjacent to the main part of the 550 species have been recorded. A reflec- Chihuahuan Desert are several disjunct, tion of their uniqueness and representa-

24 P LANT T ALK 29 P LANT T ALK 29 25 tivity is that 79% of these species are proved revealing. The study was in a mined, we can ask where the geographi- that have affected plant distributions in endemic, i.e. they are not found any- square-shaped polygon of 2855 km2, at cally rarest species are located. If we con- the past. However, during the last centu- where else outside Mexico. the southern extreme of the Chihuahuan sider only the 71 species restricted to one ry, human activities have caused these Desert. This relatively small area is state, we find that the Mexican states of plants to become even more rare. Cacti are among the most characteristic remarkable due to its unparalleled diversi- Coahuila, San Luis Potosí, Nuevo León plants of the Mexican flora, dominating ty of Cactaceae. With 75 species recorded, and Tamaulipas are the richest, with 14, The conservation challenge the landscape in many arid and semi-arid El Huizache has for its size the highest 13, 10, and 9 endemic species respective- parts of the country. However, they are concentration of cactus species in the ly. Thus, these four Mexican states are In Mexico, as well as in several other coun- not restricted to deserts – a considerable American continent. To give an idea of not only the richest in cactus diversity, tries, cacti are a highly endangered group of number of species inhabit wetter, more the extraordinary richness of Cactaceae in but also have the most endemic species. plants. It has been estimated that at least tropical parts of the country; some even El Huizache, in a single area measuring 6° one third of the Mexican species are threat- grow in tropical wet forests. latitude by 6° longitude (c. 114 km2), 41 If we repeat the analysis on a smaller ened species. In the Chihuahuan Desert, cactus species were recorded; in fact, with- scale, we discover that some cactus species natural populations of a number of species The region with the highest diversity of in this same area, 32 species were found in have extremely small areas of distribu- have been considerably affected by the col- cacti, not just in Mexico but in the whole a single locality. Moreover, 63% of the tion, which we can map with a high lection of plants for use as ornamentals or of the Americas, is the Chihuahuan Desert. cactus species found in El Huizache are degree of precision. The most extreme as collectors’ items. Although Mexican In a recent checklist, botanists have record- endemic to the Chihuahuan Desert. examples are of species that are known environmental authorities have developed a ed 315 cactus species there, some 57% of Among these, ten species are outstanding only from one or a few localities, such as legal framework to prevent illegal collecting the total number of cactus species in the for being endemic or nearly endemic to bravoanus, A. scaphirostris, of flora and fauna, there is evidence that country. The species in the desert belong to this relatively small area. With all these Aztekium hintonii, Echinocereus waldeisii, plants and seeds of Mexican cacti are still 37 genera, 17 of which are endemic. elements in mind, it is not difficult to see carmenae, Opuntia chaffeyi being illegally collected in the field. An Interestingly, almost two thirds of the that El Huizache is a focal point of global and Turbinicarpus subterraneus. additional factor affecting the conservation species are concentrated in four genera – importance for cactus conservation. status of Chihuahuan Desert cacti is the Mammillaria (73 spp.), Opuntia sensu lato Another form of rarity is when the popula- deterioration of the habitat. Agricultural (59 spp.), Coryphantha (38 spp.), and tion numbers of a species are low. development, goat and cattle raising, min- Echinocereus (30 spp.). Conversely, there How rare are rare cacti? Turbinicarpus subterraneus, for example, is ing, road construction, dam building, and are as many as 23 genera each with only known only from two populations in other human activities have modified large one or two cactus species in the region. Rarity is a relatively common phenome- southern Nuevo León; in one of the popu- parts of this desert, in cases dramatically. Cuatro Ciénegas (C/H-3901) non among living organisms. Accepting lations only a handful of individual plants A few of the cactus species in the the most simple definition, it is when a have been located, whereas in the second These forms of disturbance have had a Caption. . . Chihuahuan Desert are large, arborescent species has a very small distribution range no more than a few hundred individuals tremendous impact on cactus populations or barrel-like species, such as Myrtillocactus and/or when individuals in the popula- have been found. An even more extreme because these plants usually have slow geometrizans, Isolatocereus dumortieri, tions occur in low densities. Obviously, example is that of Opuntia chaffeyi, also growth rates, long life cycles, and low Echinocactus platyacanthus, Ferocactus pilo- rare species are more vulnerable to extinc- known only from two disjunct localities in recruitment rates from seed germination. sus, F. histrix, and several species of prickly- tion than common ones. For this reason, Zacatecas. Extensive searching at the two Furthermore, as mentioned previously, pears. In contrast, most are small, usually the study of rarity is extremely relevant to known populations of this species has cacti frequently have narrow distribution globose or shortly-cylindrical plants, like conservation biology. And Chihuahuan revealed no more than 20 individuals in ranges and are presented in low popula- members of the genera Mammillaria, cacti are unusually rare. total. Examples such as these portray cactus tion numbers. All of these factors make Echinocereus, Turbinicarpus, Aztekium and species that are both geographically and Chihuahuan Desert cacti extremely vul- Ariocarpus. They are highly cryptic, mean- An analysis of the geographical distribution ecologically rare. Such examples are not nerable to disturbance. Caption . . . Mammillaria (H-2345) ing they are extremely hard to see, as they of each of the cacti in the Chihuahuan uncommon in the Chihuahuan Desert. C-404 often look identical to the small stones Desert shows that almost 70% of the The entire cactus family is included in that make up the desert surface. species are strictly endemic to the region. If A different form of rarity in cacti is exem- Appendix II of the Convention of Fercocactus histrix (H-1594) we examine the species distribution in plified by Sclerocactus uncinatus, a wide- International Trade of Endangered Analysis of their distribution pattern more detail, we find that the great majority spread species in the Chihuahuan Desert, Species (CITES). Specifically, 33 of the shows that species diversity is not distrib- are restricted to one or a few, usually con- with numerous populations recorded species in the Chihuahuan Desert are on uted evenly. Diversity is concentrated tiguous, states. In fact, more than one third from central Mexico to southern Texas. Appendix I. Similarly, 257 Mexican towards the eastern and southeastern frag- (39.6%) of the species are restricted to one We have made over 100 counts of this Cactaceae are included in Mexico’s offi- ments of the region, in the Mexican states or two states, and two thirds (67.6%) species along 2–3 km transects, and in cial list of threatened species, of which of San Luis Potosí, Coahuila, Nuevo León occur in five or less states. Conversely, only most of the samplings we found that this 116 are found in this desert. Many and Tamaulipas, each of which has over a few of the species are really widespread, species is extremely rare in terms of num- species of Cactaceae are currently being 100 cactus species. It is in this portion of the more extreme examples being two bers of individuals. Species such as this evaluated using the new IUCN Red List the Chihuahuan Desert that most of the species of prickly-pears, Opuntia engelman- one – geographically widespread but Categories and Criteria. best known, cactus-rich localities are nii and O. imbricata, which have been locally rare – abound in the Chihuahuan located; these include El Huizache, Mier y recorded throughout the Chihuahuan Desert. Indeed, it is likely that rarity is a Noriega, Doctor Arroyo, Matehuala, Tula, Desert, including Arizona, New Mexico natural phenomenon among cacti in the Conservation strategies Jaumave and Cuatro Ciénegas. and Texas, and elsewhere well beyond the Chihuahuan Desert. It may be a result of region. past ecological factors, such as climatic Cacti are perhaps the group of organisms A recent study of cactus diversity in El changes, including to minimum and that most justify conservation activities Huizache, an area of San Luis Potosi, Once the general pattern has been deter- maximum temperatures and to rainfall, within the Chihuahuan Desert. However,

26 P LANT T ALK 29 P LANT T ALK 29 27 use that would conserve the flora and be sustainable. In countries such as in Mexico, the degree of knowledge of these basic elements is very low compared to that in developed countries.

A significant addition to the previously existing protected areas within the Chihuahuan Desert was the creation of the ‘Real de Guadalcázar Protected Natural Area’. Based on knowledge from our studies on the Cactaceae of El Huizache, a few years ago, the Government of San Luis Potosí passed a decree creating this protected area. Covering 188,758 hectares, it was designed not only to preserve the diversity of cactus species from El Huizache and surrounding areas, but also the range of vegetation types found in the area, and several other plant and animal groups The configuration of the Chihuahuan this is a difficult task due to the extraordi- whose diversity and degree of endemism is Desert is shown by the shaded area narily high beta-diversity in this region. comparatively greater there than in other and the position of El Huizache area is In order to cover the complex distribu- parts of the Chihuahuan Desert. Without indicated by the solid square. The fig- tion patterns of the numerous narrow doubt, the creation of this protected area is ures are numbers of cactus species per endemics, a network of scattered, relative- a good example of the marriage between state / endemic species. ly small, reserves has to be created. In science and conservation practice. fact, the results of our studies have been extremely useful for the identification of Despite this and other conservation potential areas for conservation. achievements, many of the critical areas of high cactus species richness and endemism BRITAIN in Flower There are several important protected are not yet protected. The number of areas areas in the Chihuahuan Desert. On the under formal protection in the travel widely in Europe and elsewhere, People living in to and appreciate, and I see this book as a way of U.S. side the most important ones are La Chihuahuan Desert definitely needs to be often with tour groups in search of flow- temperate countries with drawing people in, for them to better under- Jornada Experimental Range, Big Bend increased. The selection of these should be ers. It was on my return to England stand why we need to conserve our flora. I small floras all too frequently National Park and White Sands National based on a thorough analysis of variables from one such trip to Greece, where I Monument. During the last 30 years, such as species richness, degree of had been waxing lyrical to a group of under-appreciate their own There is no denying that the native flora several protected areas have been created endemism, taxonomic uniqueness, and British naturalists about the superb wildflowers. The native displays of of the British Isles is not a rich one. in Mexico and these have contributed in habitat diversity. Undoubtedly, conserva- displays and varieties of flowers, that I Thanks to the destruction of our flora various degrees to the conservation of the tion efforts in this region should be inten- went down in May to west Dorset to colour on our own doorstep may, during last Ice Age, and the re-flooding region’s flora and fauna. Outstanding sified, through the consolidation of the photograph the roadsides. It struck however, be perhaps the best of the North Sea and English Channel among these are the Mapimí Biosphere already existing natural protected areas and me quite forcibly that these roadsides, advertisement for the richness, variety before full re-colonization had been Reserve, the Cuatro Ciénegas Wildlife the creation of new ones. in their own way, are just as impressive achieved, we have never recovered the Refuge, the Maderas del Carmen Wildlife as those one sees in Greece – and that and fragility of plant life. BOB full complement of plant species that Refuge, and the Metztitlán and Sierra Dr. Héctor M. Hernández is Senior perhaps we too often undervalue our own GIBBONS reveals the sheer other European countries possess. So our Gorda Biosphere Reserves. However, Researcher and current Director of the flora. It also struck me that no-one had pro- splendour of Britain’s flora is now poorer than that of equivalent most of these still are exposed to negative Institute of Biology at the National duced an illustrated book to show just how areas of northern Europe. We have few endem- pressures and some of those on the University of Mexico, and Chairman of attractive our native (and some introduced!) wild wildflowers. ic species either, perhaps due to the short time of Mexican side lack sufficiently trained per- the Cactus and flowers can be en masse; and that most people in Britain isolation, and a cool climate which lengthens generation sonnel and adequate budgets. Also, only Specialist Group of the Species Survival are probably entirely unaware of what is there to be seen and times. Many high profile British ‘rarities’, such as the orchid Red about 2.5% of the Chihuahuan Desert Commission, IUCN. enjoyed, often on the doorstep. Helleborine (Cephelanthera rubra), or the sage Meadow Clary area is under any kind of protection, far E-mail: [email protected] (Salvia pratensis), to which considerable conservation efforts are too low a proportion for such an impor- This was the genesis of the book Flowers at my feet*, produced in understandably devoted, are common, even abundant, not far tant area of plant diversity. Moreover, due For more information see ‘A preliminary analysis of collaboration with, and partly in aid of, the UK charity Plantlife, away on mainland Europe. to the lack of comprehensive knowledge the diversity and endemism of Cactaceae in the to try to raise awareness of how much floral richness we still have Chihuahuan Desert region’, by H.M. Hernández on these areas, regarding, for example, and C. Gómez-Hinostrosa. In J.L. Cartron, R. in Britain, and how important it is for all of us. The conservation Yet there is more to wild plants, and their conservation, than bio- their flora and fauna, the physical envi- Felger and G. Ceballos (eds.), Biodiversity, ecosys- movement needs good photographs to help convey the message of diversity, endemism and rarity. Britain, despite an impoverished ronment (geology, soils, climate) and eco- tems, and conservation in northern Mexico. Oxford how valuable and beautiful our botanical heritage is, whether it flora, vast areas of intensively managed agricultural land, and a logical interactions, we have not been University Press (in press, due out 2002). comprises rarities, endemics or commoner flowers. For most peo- high human population density, still retains some wonderful dis- able to propose alternative forms of land ple, it is the displays of common flowers that they can best relate plays of flowers in superb and varied scenery, and this is one of

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