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LACANDON RAIN FOREST REGION
The tropical rain forests of southern and central Mexico are the northernmost extension of this ecosystem in the Americas, and once covered c. 11% of the country - forming a continuous corridor in the states of the Yucatán Peninsula, Chiapas, Tabasco, Oaxaca, Veracruz and Puebla, and occurring as well in Hidalgo and San Luis Potosí (Rzedowski 1978; Wendt 1993). However, since 1950 more than half has been destroyed for crops, lumber, cattle-ranching and oil exploration. What remains is in six large and various small ecological islands (Estrada and Coates-Estrada 1983; Dirzo and Miranda 1991).
The largest remaining segment of this northern tropical rain forest is along the eastern edge of the highlands of Chiapas, Mexico's southernmost state. The region known as Selva Lacandona is delimited to the north by the Lower Usumacinta River and the savannas and wetlands of eastern Tabasco; to the east the limits are the Usumacinta and Salinas rivers and the Guatemalan Petén (CPD Site MA13, see Data Sheet). The region continues south into Guatemala to a small extent; to the west it is delimited by the central highlands of Chiapas. The surviving Lacandon forest covers 6000 km² in the Jataté and Upper Usumacinta river basins. The Usumacinta Basin and Grijalva Basin (farther west) contain one-third of the freshwater resources of Mexico.
The region is within the Sierra Madre de Chiapas morphotectonic province, in the Northern Folded Ranges and Plateaux subprovince (Ferrusquía-Villafranca 1993). The Chiapas Highlands, from 400-2200 m, are mostly limestone with some sandstone and volcanic extrusions. The western half of the Selva Lacandona is primarily mountain ranges (to 1750 m) trending from north-west to south-east, and narrow intermontane valleys draining south-easterly. The eastern half of the region is primarily alluvial plains at low elevations, with isolated hills and valleys as major features; in general its altitude ranges from 80 m to 500 m. Much of the regional geology is based on marine and transitional sedimentary rock types from the Middle Cretaceous to Early Tertiary.
About one-fifth of the original Selva Lacandona is in the Montes Azules Biosphere Reserve (16°06'-16°49'N, c. 90°45'-91°30'W), which encompasses 3312 km² (c. 100 km × 15-55 km) including the south-central section of the forest with the lakes Ocotal, Lacanjá and Miramar (79 km²). In 1992 Mexico reserved an adjacent 663 km² to the north-east in the Lacan-tún Biosphere Reserve (619 km²) and Bonampak Natural Monument (44 km²). Montes Azules BR encompasses c. 70% of the remaining original vegetation, and has most of the vegetation types and weather found in the Lacandon region (cf. Orellana 1978).
The climate is warm and humid, with the median annual temperature above 22°C and the coolest month averaging above 18°C. The median annual precipitation is over 2500 mm, with a summer rainy season which experiences monsoons (Gómez-Pompa et al. 1994). Generally, winds from the Chiapas Highlands predominate.
According to Breedlove (1981), in Chiapas true tropical rain forest occurs only in a few locations in the flat valleys of the upper drainage of the Usumacinta River, and is surrounded by more common lower montane rain forest. Rzedowski (1978) included both in evergreen tropical forest. This true tropical rain forest is multistoreyed. Some of the most common canopy trees (50-60 m tall) are Aspidosperma megalocarpon, Brosimum alicastrum var. alicastrum, Dialium guianense, Erblichia odorata var. odorata, Guatteria anomala, Licania platypus, Manilkara zapota, Poulsenia armata, Swietenia macrophylla and Terminalia amazonia ("canshán"). The most abundant trees of the continuous second- storey canopy (25-40 m high) and trees of the understorey (10-20 m) are Alchornea latifolia, Alibertia edulis, Trichospermum grewiifolium, Bumelia persimilis, Bursera simaruba, Cassia grandis, Blepharidium guatemalense (B. mexicanum), Guarea glabra, Pleuranthodendron lindenii, Licaria peckii, Orthion subsessile, Pithecellobium arboreum, Quararibea funebris, Simira salvadorensis, Wimmeria bartlettii and Zuelania guidonia. Epiphytes are only in the upper stories; small shrubs and herbaceous cover are sparse.
The lower montane rain forest contains nearly all species found in the tropical rain forest; it is well adapted to the well-drained conditions of the region's calcareous mountains. Most of the highlands of Lacandona are covered with this formation. Its canopy is 25-45 m high, lianas are much more common, epiphytes occur throughout, and the shrub layer is dense and well developed. Additional canopy trees include Trichospermum sp., Calophyllum brasiliense var. rekoi, Ocotea rubriflora, Ocotea sp. (Nectandra sinuata), Quercus oleoides and Talauma mexicana (Miranda 1961; Breedlove 1981).
Higher ridges with montane rain forest and other types of montane forest occur to the west (cf. Calzada and Valdivia 1979). In the Lower Lacantún River Basin there is considerable seasonally flooded forest. Marshes or seasonally flooded areas have special formations, such as almost pure stands of Haematoxylum campechianum surrounding many lakes in the forest (Nations and Nigh 1980). The south-eastern Marqués de Comillas area includes drier, semi-deciduous lowland forest, and areas of savanna occur in the east (see Breedlove 1981; Gómez-Pompa et al. 1994).
There are an estimated 4000 species of vascular plants in the Selva Lacandona (Medellín 1991). Ongoing research in the Lacandon region by the Universidad Nacional Autónoma de México (UNAM) has resulted in many new collections. Studies are urgently needed to recognize threatened species, which may include the cycads Ceratozamia matudae, Dioon merolae and Zamia splendens.
The tropical rain forests of Mexico are species-rich for northern areas, particularly in the State of Chiapas where c. 1500 species of trees have been found. However, Mexican rain forests show low species diversity compared to those of Central America and South America - the diversity of trees increases in a southward gradient (Toledo 1982). For example, there are more than three times as many tree species in the Lacandon forest as in the far north-western rain forests of Huichihuayán (San Luis Potosí) and Misantla (Veracruz) (cf. Dirzo and Miranda 1991).
A few of the non-endemic canopy tree species in Mexico are found only in the Lacandon forest (e.g. Luehea seemannii, Orthion subsessile, Pourouma guianense), due to a mixture of floristic rain-forest elements of the Yucatán Peninsula and Gulf of Mexico (Wendt 1993). Floristic associations in the Lacandon forest are continuous with those in the Guatemalan Petén (Breedlove 1981) (CPD Site MA13); their compositions are relatively poorly known. The floras of the Chiapan highlands and Petén share some endemic taxa (Rzedowski 1962; Breedlove 1981), but the majority of their species are shared with Central America. Although the known endemic species restricted to the Mexican Lacandon forest are few (e.g. Yucca lacandonica), they include the startling new endemic family Lacandoniaceae, represented by Lacandonia schismatica (Martínez and Ramos 1989; Mestel 1995).
Toledo (1982) tentatively identified the Lacandon forest as one of two primary Pleistocene refugia for Mexican tropical rain forest, characterized by high rainfall (over 3000-4000 mm a year), high temperature (annual average over 25°C), and a high concentration of species. Zoogeographic data on the Lacandon region also have given evidence of isolation and protected conditions during the Pleistocene and other unstable periods (Smith 1949; Barrera 1962).
Nevertheless, Wendt (1989, 1993) found little floristic evidence of a past refuge restricted to the Lacandon region; high diversity may not be a good indicator of former refugia. The endemic taxa are mostly shared with the Petén and other areas of nearby Guatemala and Belize. The larger area (Lacandona, eastern Guatemala and southern Belize) is relatively important for rain-forest species endemism. Furthermore, in the extreme northern part of the Lacandon region the average annual precipitation can exceed 3000 mm; this is the eastern end of another endemic-rich area of rain forest known as "the crescent area". It terminates to the west in the Uxpanapa area of southern Veracruz (CPD Site MA2, see Data Sheet), which may have been a refuge (Wendt 1989).
The Lacandon forest contains important reserves of timber, such as Calophyllum brasiliense var. rekoi, Cedrela odorata, Cordia spp., Dialium guianense, Lonchocarpus castilloi, Swietenia macrophylla, Tabebuia guayacan, Talisia oliviformis and Trema micranthum. Other species of economic importance are Manilkara zapota - the "sapodilla" tree from which chicle gum is extracted; Castilla elastica var. elastica - its latex was the source of rubber ("caoutchouc") for the aborigines of Mexico; Cymbopetalum penduliflorum the flowers are used among the Maya Amerindians for flavouring and medicine (Wagner 1964); and species that bear edible fruits, such as (among trees) Manilkara zapota, Pimenta dioica (allspice), Poulsenia armata, Pouteria mammosum and many others (Miranda 1961). Peters and Pardo-Tejeda (1982) have evaluated the promising economic potential of Brosimum alicastrum ("ramón") (by using fruits, seeds, leaves, wood, latex, bark).
Several species of palms (e.g. Geonoma oxycarpa, Scheelea liebmannii) are used by the local inhabitants for roofing. Additionally, seeds, seedlings and leaves of some small palms called "xate" (e.g. Chamaedorea tepejilote, C. oblongata, C. elegans) are being removed from the forest by the millions and with increasing frequency. They are dispatched from peripheral cities by refrigerated truck to Texas, U.S.A., where they are commercialized (Marshall 1989).
Social and environmental values
The Selva Lacandona is important for management of its large watersheds and soil conservation, and encompasses a significant portion of Mexican biodiversity. About 20-25% of the Mexican species of many groups are present in the Montes Azules BR, which is only 0.16% of the Mexican territory. Among the best represented groups are birds - 345 species, over 33% of the Mexican species, including harpy eagle, black-and-white hawk-eagle (Spizastur melanoleucus), macaws and parrots; mammals - 112 species, c. 25%; and diurnal butterflies - 800 species, 44% (Medellín 1991, 1994). The forest is one of the few areas in Middle America large enough for viable populations of animals such as jaguars, ocelots, howler and spider monkeys, Baird's tapirs, white-lipped peccaries, kinkajous and caimans (cf. Vega-Rivera 1990).
The region is variously inhabited by five Amerindian groups (Lacandons, Tojolobals, Chols, Tzeltals, Tzotzils), including descendants of the pre-Columbian Maya civilization that flourished for nearly ten centuries, practising a highly diverse, long-term system of food production that showed sustained use of the tropical forest ecosystem. Among the few Mayan groups that continue using elements of this knowledge are the c. 300-450 Lacandons (Nations 1984, 1985), whose techniques of farming (a milpa style mimicking the forest's dynamics) allow the forest to regenerate without significant loss. Aspects of the Lacandon Maya subsistence and forest-management systems are being examined and applied by some institutions to demonstrate that the practices that serve them and served the Classic Maya (250-950 AD) are helpful for the modern development of sustained-yield use of tropical forest ecosystems (Gómez-Pompa 1987; Nations 1988).
The Selva Lacandona seems not to be integrated into the economic processes of Mexico or the State of Chiapas, but the situation suggests that the overall region is barely able to maintain its present population of over 150,000. About 9800 people (1990 census) live within the Montes Azules BR, especially in the south-western portion. From c. 1960, Tzeltals and Tzotzils migrated to the region from central Chiapas. Immigration of mestizo people is increasing from various parts of southern and central Mexico.
The inhabitants produce maize, cacao, rice and other crops mostly for themselves or regional use. Only crops such as the jalapeño pepper (Capsicum annuum var. annuum) represent a relatively important source of income for a few farmers, who can afford the high costs of intensive human labour and frequent applications of pesticides; these crops are shipped to Mexico City. In general, farmers invest their money in cattle, which are maintained in extensive grasslands at high environmental cost.
Important quantities of valuable woods had been obtained c. 1850-1948; most of the good trees accessible by river were gone by 1949, when the Mexican government prohibited export of unprocessed trunks (Medellín 1991). Logging roads began to open up the region in 1965. The increased rate of timber extraction is far from sustainable.
Alternatives that may provide sustainable economic development are scarcely explored or implemented. Several studies are beginning to examine the possibilities of sustained use with newly developed technologies, such as farming of butterflies and iguanas, fisheries with native species, and production of xate palms (Chamaedorea spp.) and orchids.
The region has considerable potential for tourism, especially for nature (CI 1993) and archaeological sites. The Selva Lacandona is a part of the large area dominated by the ancient Mayan culture and shared with Guatemala, Belize, Honduras and El Salvador. Major archaeological sites include Yaxchilán and Bonampak, and many still unstudied sites occur in the Lacandona.
Accelerating rates of loss of the Lacandon forest threaten its flora and fauna and the survival of its indigenous peoples. In 1943, the region was covered by more than 13,000 km² of tropical rain forest, but over half has been cleared and burned, and a significant part of the remainder is being converted by modern agricultural colonization, logging and cattle-ranching. Recently, oil exploration and road construction have significantly increased the rate of destruction of the lowland forest. Through the past 30 years, annually over 150 km² have been converted. The 1990 census found over 9800 people living within the Montes Azules Biosphere Reserve, with c. 40% concentrated in the south-western portion in 14 locales.
Planned development also threatens the future of the Selva Lacandona. One section of the plan intends to expand colonization, extending agricultural activity over 2000 km² farther into the Marqués de Comillas zone (the south-eastern area next to Guatemala). A road would be built south of the Lacantún River and parallel to the Usumacinta River and Guatemalan border to link the area with San Cristóbal de las Casas and Palenque. The Mexican forest also became home for 70,000 Guatemalans displaced by guerrilla activity, creating additional strains on forest management. The region has been threatened by a proposed binational hydroelectric project on the Usumacinta River (Wilkerson 1985), which was halted in 1992 by Mexico's president (GCTM 1992).
The Mexican scientific community and government have become increasingly concerned about social and ecological costs of economic growth in the State of Chiapas. A 1971 presidential decree set aside over 6140 km² as a Forest Reserve for the sole property and home of the Lacandons. In the middle 1970s, several institutions and agencies undertook a programme of intensive investigation in the Lacandon forest. The study recommended the creation of a Natural Reserve.
The Montes Azules Biosphere Reserve (3312 km²) was established by federal decree in 1977, and approved under UNESCO's Man and the Biosphere Programme in 1979. Mexico at the same time included the area in a Protection Forest of 26,123 km² which was established for the upper basin of the Usumacinta River and the Tulijah River Basin. The reserve is the responsibility of the Instituto Nacional de Ecología of the Secretaría de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP) (formerly in SEDESOL). A management plan was produced in November 1992. It proposes new zoning in buffer areas to regulate land uses under a realistic view for conservation and sustainable development. The reserve's exact boundaries were being established and marked in 1993. In August 1992, establishment of the following four areas protected an additional c. 810 km² in the region (Map 12): Lacan-tún Biosphere Reserve (recognized nationally) (619 km²), Chan Kin flora and fauna reserve (122 km²) and the Natural Monuments Bonampak (44 km²) and Yaxchilán (26 km²). The Sierra de la Cojolita Communal Reserve, which was established by the Lacandons, is the unique forested connection between Montes Azules BR and the protected areas in Guatemala (Gómez-Pompa et al. 1994). Studies are underway to ensure preservation of the ecological corridor between the Selva Lacandona and Guatemala's Maya Biosphere Reserve to the north-east.
The first Mexican debt-for-nature swap was signed in 1991 by the federal government and Conservation International (CI) (Excelsior 1991). These financial resources are being used to protect this forest by considering sustainable economic alternatives and providing logistical support for researchers working in the region (CI 1993). A recently restored research facility (Chajul Scientific Station) is managed by UNAM and SEMARNAP (instead of CI), and will help generate the information needed on the region and take early steps toward sustainable development and long-term conservation of the reserves. Other Mexican and U.S. institutions are among those carrying out research and conservation projects.
Scientists have a preliminary biological perspective on the region. A coalition of agencies and institutions needs to continue working to carry out a plan of action combining conservation with sound development (cf. Medellín 1991; CI 1993). The intent is to include environmental education programmes and a coordinated policy of eco-development to solve economic difficulties of the inhabitants through creative programmes without having to continue to lose large areas of natural forest. Integrated and growing activities during the past few years suggest that much of the remaining Selva Lacandona may still be saved.
Map 12. Lacandon Rain Forest Region, Mexico (CPD Site MA1)
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This Data Sheet was written by Olga Herrera-MacBryde (Smithsonian
Institution, SI/MAB Program, S. Dillon Ripley Center, Suite 3123, Washington, DC
20560-0705, U.S.A.) and Dr Rodrigo A. Medellín [Universidad Nacional Autónoma de México
(UNAM), Centro de Ecología, Apdo. Postal 70-275, 04510 Mexico, D.F., Mexico].
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