Sierras Chicas

S DIEGO E GURVICH, PABLO DEMAIO & MELISA A GIORGIS The diverse globose cactus Chicas, the eastern-most range, is bordered to of Salsipuedes and La Falda on opposite sides the east by the great Chaco-Pampas plains. The of the range. The site is part of a private cattle flora here, in the central part of the country, ranch called La Sureña. Unlike the usual places community of Argentina’s represents a meeting point between different where we expect cacti to live, the climate here is biogeographical domains1, and consequently, the temperate (14°C mean annual temperature) and mountains support a particularly high diversity sub-humid (meaning the annual precipitation is of globose cacti species, mainly from the genus about 850 mm). The vegetation is dominated by Sierras Chicas Gymnocalycium, although other genera are also tall tussock grassland interspersed throughout represented, including one Parodia species, two with rocky outcrops where cacti can be found Ecology and conservation Echinopsis species, two from Acanthocalycium (Figs 2, 3). The site was selected because seven and a Wigginsia taxon2,3. Almost all species found globose species can be found here, an uncommon in the Córdoba Mountains are endemic, includ- occurrence even in regions considered to have ing 15 of the 17 species of Gymnocalycium. The high diversity. Such diversity allows us to do a much lower diversity of columnar species (only comparative study of the environmental factors umid and shady forest, extensive our study, supported in part by the Cactus and seven can be found: Cereus forbesii, C. aeth- that affect species distribution and abundance. grasslands, moist gorges full of Succulent Society of America, and explore some iops, Stetsonia coryne, Trichocereus candicans, Throughout the approximately 40 ha study site, ferns—the mountains of Córdoba factors that are threatening this group of plants. T. lamprochlorus, Harrisia pomanensis and we established 200 1 × 1 m plots. In each plot we do not at first view look like a Cleistocactus baumannii) appears to be related counted all the individual plants of each species, promising place for cactus lovers. he Córdoba Mountains, part of the to low winter temperatures, which are known to recorded their diameter and numerous environ- However, these mountains har- Pampean range, are the easternmost of limit their southern distribution4. mental variables such as soil depth, vegetation bor one of the most diverse, curi- Tthe massive ranges in western Argentina cover, gravel cover and stone size. ous and understudied communi- (Fig 1). They can be divided into three main Analyzing these variables we found that dif- ties of globose cacti in the world. How have these ranges that run north to south. The Sierras Study site and measurements ferent species utilize different microhabitats and Hplants persisted in ann Our study site, 1200 m above seal level, is located have very different population densities. Parodia environment so different along a road called Camino del Cuadrado, which submammulosa (Figs 4, 5), a species with a wide from the desert they came crosses the Sierras Chicas to connect the cities distribution in central Argentina, from northern from? Can they survive the assaults of development? Although the cactus flora Figure 2 Our study area during the wet summer season. Unlike many other places were cacti live, pre- of the Córdoba mountains cipitation in the Córdoba mountains is fairly high. In our study area, the mean annual precipitation is is relatively well known, around 850 mm/year. Photo: D E Gurvich there is little information about their ecology or conservation status. Our working team, composed of researchers from the National University of Córdoba and of the non- governmental organization “Argentine Ecosystems,” has proposed to answer these and other questions related to this fascinating group of plants. In this article, we report some preliminary results from Figure 1 Location of the Córdoba mountains and the study area in the Córdoba province (Argentina). Colors indicate vegetation types: grasslands (brown), shrublands (dark green), open wood- lands (pale green). 2 CACTUS AND SUCCULENT JOURNAL 2006 VOLUME 78 NUMBER 3 3 D E Gurvich to the Córdoba and San Luis provinces DE Gurvich that inhabits a wide range of environments and altitudes, is the second most abundant globose cactus here with a density of 1.76/m2. Although it also inhabits a wide range of microhabitats, it is most abundant in more thickly vegetated areas, sometimes growing com- pletely beneath grass. This is one of the smallest Gymnocalycium species, reaching only 5 cm in diameter, and is I Figure 3 Rocky outcrops where most cacti species that grow here can be found. K Figure 4 A mature plant of Parodia submammulosa with buds, flowers and fruits. As with most other parodias this species is Figure 6 Gymnocalycium bruchii (right) and G. quehlianum growing close together. These two individu- self-fertile, which guaran- als were marked (note the metal tags) for a phenological study in progress. tees seed production. L Figure 5 Flower of G Rivera altitude (G. mostii lives at lower altitude than G. Unlike G. monvillei, G. mostii is restricted to the Parodia submammulosa. monvillei, with an overlapping distribution in a Córdoba province. narrow elevation range). G. monvillei is probably Echinopsis aurea (Fig 11) is found in a micro- the most widespread species of the genus in the habitat similar to G. mostii, but with even less characterized by an almost mountains of the Córdoba and San Luis prov- vegetative cover. Its density is 0.22 individuals/ flat body, a huge taproot inces, inhabiting a wide range of environments. m2. This species has a large geographical range and the capacity for vegeta- inhabiting the Córdoba, San Luis, La Rioja and tive reproduction, forming Figure 7 A mature individual of Gymnocalycium Catamarca provinces. colonies which are usually monvillei. Flowers can vary from pale (almost Gymnocalycium amerhauseri and G. quehl- comprised of 4 or 5 heads, white) to dark pink. The color and size of the ianum (Figs 6, 12–14) have narrower ecological but eventually can become spines is quite variable among the individuals in niches than the other species listed, inhabiting 305. a single population. places with intermediate stone sizes (we catego- Gymnocalycium mon- rized stone size classes as small, between 0 and villei and G. mostii (Figs 5 cm of diameter; intermediate, between 5 and 7–10) are morphologically 20 cm; and big, from 20 cm to massive outcrops) similar, but for the most and moderate vegetation. Their densities are part each exploits a dif- 0.52 and 0.17/m2, respectively. It is interesting ferent ecological niche. to note that although both species have similar Gymnocalycium monvil- environmental requirements, they are not found lei (0.36/m2) is about twice living together. The populations of both species as abundant as G. mostii lie about 500 m apart from each other, indicating (0.15/m2). Although both space segregation due probably to competition for D E Gurvich species inhabit places with suitable places to germinate and grow, although we Patagonia (Río Negro and Mendoza provinces) to a high stone cover, G. monvillei occupies more can not rule out some other environmental factor the province of Catamarca in the northwest of the vegetated sites (and even the shady and humid not measured or recognized by our study. Both country, grow in densities here of 1.03 individu- southern slopes), while G. mostii can be found in species are endemic of the Córdoba province, but las/m2 and inhabit a wide range of microhabitats, exposed areas on more extensive plots of bare soil with different range sizes. While G. quehlianum from places with a thick cover of vegetation to with less vegetative cover. It would be interesting is common in the province, G. amerhauseri is places with rocky, bare soil. to study these species in sites where the other micro-endemic to the Sierras Chicas range and a Gymnocalycium bruchii (Fig 6), an endemic is not present, since they are also segregated by few adjacent areas. F Bloss 4 CACTUS AND SUCCULENT JOURNAL 2006 VOLUME 78 NUMBER 3 5 P Wan J Figure 11 A mature individual of Echinopsis aurea with their typical yellow flowers. This species has a wide geographic distribution and is also quite variable in shape. At high altitude it is more spherical with short spines, while at lower altitudes it grows more cylindrically and with longer spines. L Figure 12 Gymnocalycium amerhauseri in flower and bud. At the moment, this species is known only from the Sierras Chicas range and a few adjacent areas and can be considered a micro- endemic species. S Alfonso F Bloss I Figure 8 A close-up view of the flower of Gymnocalycium monvillei. S Alfonso that there are important ecological differences largest city in Argentina, with approximately 1.3 among them promoting differential uses of the million inhabitants. In the past few years there has environment. We also found evidence for spatial been an exodus of people from the city to nearby segregation between G. amerhauseri and G. que- small towns (suburbs) located mainly in the hlianum. Although they inhabit similar niches, mountains. Some of these cities have increased they are not to be found together. These two their population significantly in the recent years, mechanisms seem to promote the high diversity with a direct effect on the natural areas sur- found in the study area, and probably in other rounding them. For example, the population of areas with high cactus diversity. the towns close to the study area has increased from 18,859 to 42,694 from 1970 to 2001. The urbanized area of the mountains has increased Conservation status and risks from 325 to 1299 ha in the same period8.

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