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The Uxpanapa-Chimalapa region covers c. 7700 km² in extreme south-eastern Veracruz and eastern Oaxaca states (Map 13). The region includes the Atlantic slope of the eastern portion of the Isthmus of Tehuantepec, mostly in the drainage of the Coatzacoalcos River and its major tributary the Uxpanapa River, and extends from the Gulf of Mexico lowlands southward to the highlands of the continental divide; a part of eastern Chimalapa is in the Grijalva River drainage.
The Uxpanapa section (c. 2600 km²) includes the parts in Veracruz and in the municipality of Matías Romero (the "Colonia Cuauhtemoc") in Oaxaca. The Chimalapa section (c. 5100 km²) encompasses essentially all of the municipality of Santa María Chimalapa and the gulf slope and highlands of the municipality of San Miguel Chimalapa, both in Oaxaca; the southern boundary of the region is the southern boundary of the montane forests of the Sierra Atravesada.
Seven physiographic regions may be distinguished (cf. Ferrusquía-Villafranca 1993):
1. A karst area in northern Uxpanapa (pictures), with relatively little macrorelief but numerous small to large limestone outcrops. Average elevation 100-150 m.
2. An eastwest strip in central Uxpanapa, with deep, flat alluvial soils formed by northflowing rivers and alluvial outwash from the mountains to the south. Average elevation 100-130 m.
3. In southern Uxpanapa northern Chimalapa, an area of steep hilly terrain fringing the Sierra de Tres Picos, with very deep soils, and the relief becoming gradually higher toward the sierra.
4. The Sierra de Tres Picos (picture), a small granitic system with a number of steepsided peaks reaching 1450 m, in north-central Chimalapa.
5. The eastwest Río del Corte Valley (Upper Coatzacoalcos River) in central Chimalapa. The river is mostly at an elevation of 80-250 m, its tributaries going through a complexly dissected central area with no major flats in the montane areas.
6. The Sierra Atravesada (or Sierra Niltepec) of southern Chimalapa, a major eastwest range of mostly granitic and metamorphic substrates, which forms the continental divide and includes peaks such as Cerro Azul (the highest - 2250 m) and Cerro Baúl (2050 m). Its eastern part is drained by the Negro River, a tributary of the Grijalva River. This range along with the Sierra de Tres Picos forms the north-western end of the Sierra Madre de Chiapas (Wendt 1983).
7. The limestone Sierra Espinazo del Diablo of north-eastern Chimalapa and a small part of extreme south-eastern Uxpanapa, reaching 1350 m.
Moist gulf winds moving south across the Isthmus of Tehuantepec produce one of the highest rainfalls in lowland Mexico in the Uxpanapa area. Average annual precipitation is 2800 mm in the west and 4400 mm in the east (Comisión del Papaloapan, unpublished). Even higher rainfalls probably occur in the relatively unknown Sierra de Tres Picos. To the south (leeward) of this range in Chimalapa, the precipitation in the Río del Corte lowlands is less than in Uxpanapa, probably mostly 2000-3000 mm or less in some areas, and greatest in the lower (western) part of the valley. The higher portions of the Sierra Atravesada and Sierra Espinazo del Diablo are clearly very wet (but without records).
Rain is seasonal, with a marked dry season from March through May, when monthly rainfall averages 60-100 mm in Uxpanapa. The wettest months are June to October. The Uxpanapa area forms the western end of a roughly crescent-shaped lowland of high precipitation ("the crescent area") that extends eastward in Mexico to southern Tabasco and northern Chiapas (Wendt 1983, 1989, 1993).
Average annual temperature in the lowlands is 24°-25°C; monthly average temperatures vary from around 20°C in January (and as low as 8°-10°C at night), to above 28°C in May. Daytime temperatures can exceed 41°C (Comisión del Papaloapan, unpublished). The highlands are cooler, but frosts appear to be rare and snow unknown.
The Uxpanapa-Chimalapa region includes the only major remaining well-developed rain forest in Mexico apart from the larger but much more disturbed Lacandon forest of Chiapas (Ewell and Poleman 1980) (CPD Site MA1, see Data Sheet). On the lowland and hill areas of Uxpanapa and northern Chimalapa are evergreen and semi-evergreen tropical rain forests, which vary according to the substrate (Wendt, unpublished):
1. Karst area forests - with irregular canopies c. 25-35 m high, and many gaps due to tree falls and irregular substrate. In the drier western areas, a notable portion of the trees shed their leaves in the dry season. Common canopy trees include Bernoullia flammea, Brosimum alicastrum var. alicastrum, Bursera simaruba, Cedrela odorata, Chione chiapasensis, Dendropanax arboreus, Dialium guianense, Guarea glabra, Lonchocarpus guatemalensis, Omphalea oleifera and Spondias radlkoferi.
2. Hill forest - evergreen, on the deep soils of the hill area, with a continuous canopy c. 3040 m high. Common or characteristic canopy species include Brosimum guianense, B. lactescens, Calophyllum brasiliense var. rekoi, Cordia megalantha, Dialium guianense, Elaeagia uxpanapensis (picture), Enterolobium schomburgkii, Eschweilera mexicana, Hirtella triandra subsp. media, Licania hypoleuca var. hypoleuca, L. sparsipilis, Pouteria neglecta, Sloanea meianthera, Spondias radlkoferi, Sterculia new sp. Wendt & E. Taylor, Tapirira new sp. Wendt (picture) and Terminalia amazonia. In many areas Sloanea tuerckheimii is the most common subcanopy tree.
3. Forest of the central Uxpanapa alluvial plain - almost completely destroyed, its original composition is not well known. It appears to have been more similar to the hill forest, with Ceiba pentandra, Dialium guianense, Terminalia amazonia and Vochysia guatemalensis important.
4. Riparian forest - the most common tall trees are Ficus insipida and Ocotea uxpanapana.
The Chimalapa area is notable for its very large tracts of undisturbed and little disturbed lowland and montane forests; especially, there are large transects of undisturbed lowland rain forest to montane cloud forest. The hill and riparian forests of Uxpanapa extend into the Chimalapa area. Hill forest is widespread in the lower Río del Corte Valley and areas near the Sierra de Tres Picos and Sierra Atravesada. The lower elevations of the dissected topography of the central Río del Corte Valley support a complex mixture of lowland oak forest (Quercus oleoides and other oaks), pine forest (Pinus oocarpa), tropical rain forest, and semi-deciduous tropical forest, with some elements of montane mesic forests (e.g. Liquidambar styraciflua, Pinus chiapensis); this mixture, all at less than 600 m, is perhaps unique in Mexico. Very small areas of rock outcrop near the river support unique xeric vegetation including species of Agave, Beaucarnea and Yucca.
Montane areas of the Sierra de Tres Picos and Sierra Atravesada support diverse cloud forests, which may represent the largest area of undisturbed cloud forest in Mexico and Central America. These are isolated from other cloud forests of Oaxaca, Veracruz and Chiapas by lower and/or drier intervening areas. Among the genera of canopy trees with one or more common species are Alfaroa, Billia, Cedrela, Clethra, Genipa, Inga, Liquidambar, Magnolia, Matayba, Oreomunnea, Pinus, Podocarpus, Quercus, Ticodendron and Weinmannia, along with numerous species of Lauraceae. Elfin forest occurs along the crest of the Sierra de Tres Picos and on some peaks of the Sierra Atravesada. Extensive pine forests with Pinus oocarpa and other pines are found in the lower, eastern Sierra Atravesada. The montane forests of the Sierra Atravesada become drier south of the continental divide and give way to tropical deciduous forest at lower elevations on the Pacific slope (beyond our region).
The first collections in the Uxpanapa area were those in the early 1970s by the Flora de Veracruz project (cf. Márquez-Ramírez, Gómez-Pompa and Vázquez-Torres 1981), except for some in the 1930s along the Coatzacoalcos River in the west. Since 1980, the Colegio de Postgraduados, Chapingo, has had an intensive collecting programme (MacDougall 1971; Myers 1980; cf. Wendt 1987). The Uxpanapa lowlands are now relatively well known; over 200 species of canopy trees have been recorded. The entire region is estimated to have 3500 vascular plant species.
Wendt (1989) reported on the high endemism of the Uxpanapa flora (including northern Chimalapa), and proposed the area as a refuge for rain-forest species during cycles of climatic deterioration during the Pleistocene and earlier. His partial lists include at least 36 species apparently endemic to the Uxpanapa area and 11 more endemic to the high precipitation crescent area. Many other species are known in Mexico only from this area. Wendt (1993) has shown that the Uxpanapa area is perhaps the most important centre for endemism in canopy trees of the Mexican rain forest.
Several genera and one family are known in Mexico only from Uxpanapa-Chimalapa (Wendt 1988, 1989), and more genera are known only from the crescent area (cf. Wendt 1993). Noteworthy rain-forest trees include the monotypic genus Chiangiodendron, abundant only in Uxpanapa (although also known from Chiapas) and the only New World member of its tribe (Wendt 1988); Eschweilera mexicana (endemic to Uxpanapa-Chimalapa), the only representative of the Lecythidaceae in Mexico (Wendt, Mori and Prance 1985); many other endemic canopy tree species including Ocotea uxpanapana, Sterculia new sp. (picture) and Tapirira chimalapana; two new flagelliflorous understorey species of Annonaceae, one of which appears to be a new genus (Schatz and Wendt, unpublished); and a new understorey genus of Rutaceae (Chiang, unpublished). All of the canopy trees just mentioned are very common to co-dominant elements of the rain forests of the region. A number of other abundant canopy trees are more widespread, but restricted in Mexico to Uxpanapa-Chimalapa (e.g. Pouteria torta subsp. tuberculata).
The Chimalapa area had been only sporadically collected (MacDougall 1971) until the Colegio de Postgraduados, Chapingo, began intensive collecting in 1984. However, due to the very remote nature of most of the area and its great vegetational diversity, it remains poorly known floristically. Its rain forests are mostly similar to the Uxpanapa hill forests and share many of their unique species. The montane forests include many species also known from the Sierra de Juárez of northern Oaxaca (CPD Site MA3, see Data Sheet) and the cloud forests of Chiapas, but already have yielded a number of new species in both the tall forests and elfin forests. The Oreomunnea forests are probably better developed in Chimalapa than in any other part of Mexico, and as well as less disturbed. Preliminary studies of the xerophytic outcrop vegetation near El Corte River indicate high endemism in its small flora.
The region contains important timber resources, including not only such widespread high quality tropical woods as Cedrela odorata (tropical red-cedar), Calophyllum brasiliense var. rekoi (Santa María) and Swietenia macrophylla (bigleaf mahogany), but important endemics such as the new, undescribed species of Sterculia, which has been much used locally in the manufacture of fine plywood. Furthermore, a large native population of the important fruit tree Pouteria sapota (the "zapote mamey") is present; there are few such populations elsewhere. Several non-timber montane species are important in the local economy, especially "palmita" (Chamaedorea sp.), the leaves of which are carefully harvested without killing the plant, and sold for ornamental purposes. Caballero et al. (1978) emphasize the usefulness to local peoples of a large proportion of the native Uxpanapa species. The endemic species still include many that have never been investigated for possible uses, since the region was virtually uninhabited until the past few decades.
Social and environmental values
The Uxpanapa-Chimalapa region is one of the most important remaining natural areas in Mexico for wild animals. There are large populations of such threatened species as jaguar and Baird's tapir, together with spider monkeys, tayra, agouti, kinkajou and many others.
Birds include the northernmost population of quetzal, large populations of curassow, and many others; harpy eagles have been reported in the Chimalapa area. There are no Endemic Bird Areas (EBAs) in the region, but the whole range of the highly localized and threatened Nava's wren (Hylorchilus navai) is restricted to karst forest in Uxpanapa and immediately adjacent Chiapas; the entire genus Hylorchilus is endemic to the Mexican karst rain forest (Atkinson et al. 1993).
The montane forests of the Sierra Atravesada contain a biogeographically distinctive herpetofauna with a significant endemic component; Campbell (1984) states that this range represents "a pivotal point of major importance in the distribution of Middle American cloud-forest reptiles and amphibians" - yet most of the range remains herpetologically unknown.
Uxpanapa and Chimalapa form the headwaters of the Coatzacoalcos River drainage, which has important downstream cities (Coatzacoalcos, Minatitlán) where flooding has increased since development of the Uxpanapa area began. Adequate forest and rational management are essential for control of soil erosion, flooding and water quality, especially considering the steep fragile soils of southern Uxpanapa and northern and eastern Chimalapa.
The region has potential for tourism, especially with regard to the animals, the beautiful rock formations and flora of the karst zone, and the true wilderness quality of much of Chimalapa.
Uxpanapa did not support a large indigenous population, and except for logging operations and other development near the Coatzacoalcos River (Río del Corte) in the west, it was almost completely undeveloped and unsettled until the early 1970s, when the federal government (Comisión del Papaloapan) started a major project in the Veracruz portion of Uxpanapa to resettle indigenous Chinanteco people displaced by the Cerro de Oro dam. Huge areas were cleared mechanically, mostly on the deep flat soils of the central part, but including some karst areas completely unsuited for agriculture or livestock. Early large-scale agricultural schemes (notably with rice) were conspicuous failures (Ewell and Poleman 1980), although many areas proved suitable for smaller scale subsistence agriculture. Large areas of closer hill forest were burned by escaped "milpa" fires during spring; some was converted into pasture. There also have been incursions into the bordering Chimalapa forests.
By 1980, perhaps one-half of the Uxpanapa area still supported primary forest. During the 1980s, the attrition rate in the Veracruz part of the area was slower, due to the limited number of settlers allowed, a partially enforced statewide ban on cutting of primary forest, and the fact that the prime agricultural lands had already been cleared (cf. Wendt 1993). However, logging in the Colonia Cuauhtemoc area in Oaxaca has intensified, often including part of the Chimalapa area and advancing toward the Sierra de Tres Picos. Large tracts of forest are subsequently cleared for agriculture, grazing and colonization.
The Comisión del Papaloapan in the 1980s developed a master plan for the Veracruz part; included were areas designated for forestry and for biotic reserves. Many karst areas and hill areas with extreme slopes were not to be developed. However, the Veracruz part went completely into State responsibility in 1985; its future is unclear. The karst forests are less threatened at present due to the difficulty of logging and the low agricultural potential of their soils. However, the rich hill forests in both Veracruz and Oaxaca have, as of 1995, almost vanished.
The history of the Chimalapa area has been quite different. Since pre-Hispanic times the Chima (a small Zoque population) have been there, centred in the area of the present town of Santa María Chimalapa. The Chimas communally own all of the municipality of Santa María Chimalapa, but the right to use parcels of the land may not only be inherited but bought, including by outsiders who are accepted as "comuneros". A similar situation pertains in the south-eastern portion of the area for some communal lands of San Miguel Chimalapa.
Before the 1970s, the only significant impact was near the town of Santa María and a few small areas westward, and along the Chiapas border to the east. Since then, logging, agriculture and/or settlements have increased westward and along the borders with Veracruz and Chiapas. As of 1995, only the vast heart of the Chimalapa area - Sierra de Tres Picos, upper Río del Corte Valley, much of the Sierra Atravesada - remains little disturbed and completely without roads. However, several large-scale developments have been proposed, including major dams on El Corte River and its tributaries as part of an irrigation scheme for the southern dry side of the Isthmus of Tehuantepec, and also major internationally financed forestry projects. A proposed second trans-isthmian highway to connect the area of Acayucán, Veracruz with Cintalapa, Chiapas would cut diagonally across Uxpanapa and north-eastern Chimalapa, further threatening the region due to concomitant colonization.
For the Uxpanapa area, no official plan for conservation exists. Before the dissolution of the Comisión del Papaloapan, the agency's field personnel in Uxpanapa were much interested in the possibility of parks and tourism to boost the local economy and protect the watersheds. Nevertheless, presently there appears to be no effort within the government to establish parks or to preserve part of the area.
There has, however, been much interest in the future of the Chimalapa area within the now vigorous Mexican conservation community, including the formation in 1991 of a National Committee for the Defense of the Chimalapas. Interest thus focused has led to increased appreciation by local people for the unique nature of the area, international support for studies of the zone, an attempt to solve boundary disputes and encroachments, and a government proposal for a Biosphere Reserve, which however is opposed by the local populace and some conservation groups. Although details are still sketchy, present plans made with greater local input call for a "campesino"-administered Biological Reserve.
Map 13. Uxpanapa-Chimalapa Region, Mexico (CPD Site MA2)
Atkinson, P.W., Whittingham, M.J., de Silva Garza, H., Kent, A.M. and Maier, R.T. (1993). Notes on the ecology, conservation and taxonomic status of Hylorchilus wrens. Bird Conserv. Intl. 3: 75-85.
Caballero, J., Toledo, V.M., Argueta, A., Aguirre, E., Rojas, P. and Viccon, J. (1978). Estudio botánico y ecológico de la región del río Uxpanapa, Veracruz. Núm. 8. Flora útil o el uso tradicional de las plantas. Biótica 3: 103-144.
Campbell, J.A. (1984). A new species of Abronia (Sauria: Anguidae) with comments on the herpetogeography of the highlands of southern Mexico. Herpetologica 40: 373-381.
Ewell, P.T. and Poleman, T.T. (1980). Uxpanapa: reacomodo desarrollo agrícola del trópico mexicano. Instituto Nacional de Investigaciones sobre Recursos Bióticos (INIREB), Xalapa, Veracruz.
Ferrusquía-Villafranca, I. (1993). Geology of Mexico: a synopsis. In Ramamoorthy, T.P., Bye, R., Lot, A. and Fa, J.E. (eds), Biological diversity of Mexico: origins and distribution. Oxford University Press, New York. Pp. 3-107.
MacDougall, T. (1971). The Chima wilderness. Explorers J. 49: 86-103.
Márquez-Ramírez, W., Gómez-Pompa, A. and Vázquez-Torres, M. (1981). Estudio botánico y ecológico de la región del río Uxpanapa, Veracruz. Núm. 10. La vegetación y la flora. Biótica 6: 181-217.
Myers, N. (1980). Conversion of tropical moist forest. National Academy of Sciences, Washington, D.C. 205 pp.
Wendt, T. (1983). Plantae Uxpanapae I. Colubrina johnstonii sp. nov. (Rhamnaceae). Bol. Soc. Bot. Méx. 44: 81-90.
Wendt, T. (1987). Plantae Uxpanapae III. A new species of Biophytum (Oxalidaceae) and five genera new for the Mexican flora. Brittonia 39: 133-138.
Wendt, T. (1988). Chiangiodendron (Flacourtiaceae: Pangieae), a new genus from southeastern Mexico representing a new tribe for the New World flora. Syst. Bot. 13: 435-441.
Wendt, T. (1989). Las selvas de Uxpanapa, Veracruz-Oaxaca, México: evidencia de refugios florísticos cenozoicos. Anales Inst. Biol. Univ. Nac. Méx., Ser. Bot. 58: 29-54.
Wendt, T. (1993). Composition, floristic affinities, and origins of the canopy tree flora of the Mexican Atlantic slope rain forests. In Ramamoorthy, T.P., Bye, R., Lot, A. and Fa, J.E. (eds), Biological diversity of Mexico: origins and distribution. Oxford University Press, New York. Pp. 595-680.
Wendt, T., Mori, S.A. and Prance, G.T. (1985). Eschweilera mexicana (Lecythidaceae): a new family for the flora of Mexico. Brittonia 37: 347-351.
This Data Sheet was written by Dr Tom Wendt (Plant Resources
Center, University of Texas, Botany Department, Austin, Texas 78713-7640, U.S.A.).
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