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Interior Dry and Mesic Forests: CPD Site SA24


Location:  North-eastern Bolivia, primarily in Beni Department, extending into Iturralde Province of La Paz Department and a little of Pando and Cochabamba departments, between latitudes 11°-16°S and longitudes 63°-69°W.
c. 270,000 km²: savannas 150,000 km², forests 120,000 km².
130-235 m.
Mosaic of about eight different basic types of savannas and forests, many seasonally flooded; wetlands (marshes, swamps, lagoons).
c. 5000 species, 1500 in savannas; species highly adapted to changing hydrological, edaphic and climatic conditions; transitional zone with floristic elements of cerrado from the west, southern limit for Amazon forest and northern limit for Gran Chaco.
Useful plants: 
Forage grasses and legumes, timber species, Hevea rubber, Brazil nuts (Bertholettia), fruit trees, local cultivated strains of peanut (Arachis) and cassava (Manihot).
Other values: 
Potential genetic resources; abundance of many species of animals, including threatened species; several Amerindian peoples; ecotourism.
Overgrazing, fire, altered drainage, logging, road construction.
Biosphere Reserve and Biological Station; Amerindian territories; Forestry Reserves; Regional (rangeland) Park, private reserves.

Map 60: CPD Site SA24


The Llanos de Mojos (Moxos) region of northern Bolivia is north-east of the Andes in the lowlands, mostly east of the Beni River, and west of the Serra dos Pacaás Novos and Chapada dos Parecis of Brazil (Rondônia and Mato Grosso). This region is the southernmost extension of the Amazon Basin, and the third largest complex of savannas in South America. The sediments of the Llanos are mostly of alluvial origin from the late Pleistocene and Quaternary (Campbell, Frailey and Arellano-L. 1985); beneath is a Tertiary marine molasse. The region belongs to a pericratonic basin underlain by the ancient Brazilian Shield, with various faults and diaclasations (Hanagarth and Sarmiento 1990). The plain has little local relief, but elevational change of a few meters may determine an area's water regime and biota.

Three main river systems drain the Llanos de Mojos, uniting northward to form the Madeira River of Brazil, which is the major south-western tributary of the Amazon. From Andean watercourses in western Bolivia derives the Beni River, while the Mamoré flows centrally from watercourses along the rest of these Andes; the Guaporé (or Iténez) drains from the low east bordering Brazil. The decline of these rivers on the plain is extremely slight, e.g. the Mamoré falls only 170 m during its course of c. 1500 km. Numerous meanders and abandoned channels exist.

The region of the Llanos de Mojos is transitional between the equatorial zone and the tropical summer-rain zone; it experiences high rainfall during the summer months, and dry periods of 23 months between June and August. The mean annual precipitation decreases eastward with greater distance from the Andes, e.g. from over 2000 mm in Rurrenabaque to 1300 mm in Magdalena. Nonetheless, any given locality has large fluctuations; e.g. at Estancia Espíritu (with 18 years of data), the annual precipitation varies from 1322 mm to 2454 mm. Very heavy rainfall for a few hours, which can reach more than 200 mm, is also characteristic in the Llanos (Hanagarth and Sarmiento 1990).

Various savannas and forests are inundated seasonally from overflow of several large Andean rivers, as well as accumulation of local rainwater. Due to outcroppings of the Brazilian Shield along the Madeira, Beni and Guaporé rivers, the waters slow; occasionally secondary tributaries even flow backward during the height of the rainy season (Beck 1983)! During the rainy season the rivers carry substantial loads of sediments and organic substrates. The floods cover large areas of the Llanos, and may remain for 5-7 months in some areas. Every 6-12 years, 80-90% of the region is inundated. This greater cyclical flooding may be an effect of the Pacific Ocean's El Niño current, but there has been no study correlating the phenomena.

The mean annual temperature is c. 26°C. Prevailing winds come from the north to north-east, but between May and September contrasting southern cold fronts ("surazos") frequently reach the Llanos de Mojos. The temperature can drop 10°C or more in a few hours and the cooler misty weather can last a day to about a week. The minimum temperature reported is 6°C in the central Llanos at Santa Ana de Yacuma.

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The Llanos de Mojos region is an expansive mosaic of different vegetation types. Humid savannas predominate, interrupted and bordered by a variety of forest communities (Ribera 1992; Foster 1989). Preliminary studies in several areas have revealed a high diversity of distinct savannas and forests, each type varying in species adapted to a particular habitat complex usually with a radically changing water regime - waterlogged to varyingly inundated or draining, and seasonal drought (Haase and Beck 1989; Beck 1984).

The savannas of the western to north-western portion of the Llanos de Mojos ("sabanas oligotrofas") (see Map 60) consist of grasslands dominated by bunchgrasses and termite mounds with scrub vegetation, due to the poor, generally acid soils. Characteristic species are Leptocoryphium lanatum and Trachypogon plumosus (Gramineae). One vegetation type ("sartenejal") within this association is characterized by a hummock-and-gully relief (varying by a few dm), with Mesosetum penicillatum (Gramineae), Bulbostylis juncoides (Cyperaceae) and shrubs such as Macairea scabra (Melastomataceae). Better draining areas have numerous large termite mounds with several species of shrubby Melastomataceae and small trees, e.g. Xylopia aromatica (Annonaceae). Limited areas of palm swamp occur, with Mauritia flexuosa and Mauritiella aculeata.

The central portion of the Llanos de Mojos, between the Beni and Mamoré rivers, generally is flooded much more than the north-western and northern portions. These floodplains ("sabanas inundables") have a high diversity of aquatic and marsh vegetation with good forage grasses, such as Luziola, Hymenachne and Leersia. Permanently somewhat wet areas consist of swamps dominated by sedges and Thalia geniculata (Marantaceae). Several enormous waterlogged swamps ("humedales") marked by Cyperus giganteus occur, e.g. surrounding Rogaguado Lake. In the drier "semialturas" large areas with open stands of the palm Copernicia alba are found. East of the Mamoré River research is lacking, but open palm forests (or "sabanas de palmares") appear to predominate and there apparently are waterlogged swamps like the humedales of the Magdalena area with a variety of different species (Ribera 1992; cf. IBGE and IBDF 1988).

The savannas of the northern Llanos de Mojos ("sabanas del cerrado") between the Beni and Iténez/Guaporé or Mamoré rivers are less heavily inundated and have affinities to the cerrado vegetation of central Brazil (see CPD Site SA21). These grasslands have a lateritic hardpan and typical cerrado genera: Kielmeyera and Caraipa (Guttiferae), Byrsonima (Malpighiaceae) and Qualea (Vochysiaceae).

Based on broad geographic and ecological conditions, four main types of forest may be distinguished in the region, which meet or intermingle with the savannas (Map 60). In the far north (mainly in Pando Department), extending southward across the Madre de Dios and lower Beni rivers and narrowly along the Iténez/Guaporé, is the southernmost portion of the Amazon forest ("bosque húmedo amazónico"), with typical species including Hevea brasiliensis ("siringa") and Bertholletia excelsa ("castaña"). Along the Andean foothills occurs more humid rain forest ("bosque muy húmedo de pie de monte") (e.g. see Madidi-Apolo Data Sheet, CPD Site SA36), which contrasts strikingly with the oligotophic savannas (and other forest types) of the Madidi River to Ixiamas area west of the Beni River (cf. Parker and Bailey 1991).

On relatively recently formed dikes along active rivers and their abandoned meanders occurs gallery forest ("bosque de galería"). A more diverse forest considered to be older gallery forest is found in large to small strips on long-abandoned river courses, and forest islands covering a few to several thousand ha are found throughout on higher ground. Perhaps some forest strips became segmented into islands by fires (mostly human-set). Scattered through the Llanos on small patches of sodic soils are thorny forest islands with Machaerium hirtum (Leguminosae).

The southern portion of the region is bordered with a seasonal, but mostly evergreen forest ("bosque húmedo de llanura"). In the midwestern Mamoré Basin 50 km east of the Andean foothills, this forest is being studied in the Beni Biosphere Reserve at the Beni Biological Station (Forsyth 1989; Campos-Dudley 1992). Six to ten forest communities of relatively limited species diversity have been distinguished, from 515 m to 3035 m in height, well-draining to varyingly inundated, and some even with deciduous trees predominant.

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Only a few studies have been made on the flora of the Llanos de Mojos. There may be 1500 species in the savannas of the whole region, and 5000 species mostly in the forests in the Chimane Ecosystem area of the Beni Biosphere Reserve with adjacent units to the south (Foster 1989). Phytosociological research near the Yacuma River (a major midwestern branch of the Mamoré River) documented c. 500 species (Beck 1983) and some 150 km north-west across the Beni River c. 600 species were found, with less than 20% in common (Moraes and Beck 1992). These areas yielded 6-8 new species: in Boelckea - a new genus of Scrophulariaceae (Rossow 1992), and Bellucia (Melastomataceae), Casimirella (Icacinaceae), Lantana (Verbenaceae), Peltodon (Labiatae), Wolfiella (Lemnaceae) and Andropogon (Gramineae). The most abundant families were Gramineae, Cyperaceae and Leguminosae; Xyridaceae, Eriocaulaceae, Lentibulariaceae and Melastomataceae were also important.

The number of endemic species is unknown, but probably not high. The rain-forest flora is essentially Amazonian, where there is a continuing yield of intriguing discoveries, e.g. the shrub Styloceras brokawii (Buxaceae) (Gentry and Foster 1981). In areas with less inundation, there are elements of the Gran Chaco flora (CPD Site SA22).  The cerrado species are more common in the drier (anthropogenic) savannas at forest margins and on lateritic soils in the north.  Most of the savanna species seem to be widespread, occurring in similar wetland complexes in central Brazil and northern South America.

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Useful plants

Fruits of some trees and shrubs are locally consumed, particularly species of Rheedia (Guttiferae), Salacia (Hippocrateaceae), Myrcia (Myrtaceae) and various palms, which are also used for extraction of oils, palm hearts, fibres (e.g. "jatata", Geonoma diversa - Rioja 1992) and construction. Wild relatives of pineapple (Ananas comosus) are found and numerous cultivars of peanut (Arachis hypogaea) are potential genetic resources. Historical works describe a wide range of economically important species and cultivars (Eder c. 1772); some are still grown, such as sweet and bitter cassava (Manihot), red pepper (Capsicum), squash (Cucurbita), gourd (Lagenaria) and cotton (Gossypium).

The high diversity of grasses, sedges and legumes is a potential source for selection and breeding of improved forage varieties for tropical to subtropical climates, particularly in the grasses Paspalum, Panicum and Schizachyrium, as well as the legumes Centrosema and Aeschynomene. Some valuable timber species such as "tajibo" (Tabebuia spp., Bignoniaceae) and "palo María" (Calophyllum brasiliense, Guttiferae) are still relatively abundant; others have become scarce. The Llanos could be an important genetic provenance of the species that have reached their distributional limits here.

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Social and environmental values

The region's transitional mosaic of different ecosystems with the large amount of edge habitats provides refuges for multitudes of wild animals, including 13 of Bolivia's 18 threatened tropical species. Among the richness of birds (c. 500 species, Parker 1989) are an incredible diversity of waders (over 18 species) and large populations of regionally distributed birds (e.g. the rhea, Rhea americana), as well as several species from the Northern Hemisphere known to over-winter or migrate through the Llanos. A preliminary bird survey of the savannas near Ixiamas documented 135 species, and this avifauna had little in common with the birds of the savannas 150 km to the south-east near Yacuma (Parker and Bailey 1991).

The main portion of the East Bolivian lowlands Endemic Bird Area (EBA B36) is in the Llanos de Mojos region. This EBA comprises just three bird species, blue-throated macaw (Ara glaucogularis), buff-bellied hermit (Phaethornis subochraceus) and unicoloured thrush (Turdus haplochrous). The macaw and thrush are listed as threatened. The macaw was known only from trade until a small breeding population was found in 1992, and there is just a handful of sightings of the thrush from four localities - in 1992 from just inside the Beni Biosphere Reserve.

The many mammals living in the region include eight monkey species, five cat species, maned wolf (Chrysocyon brachyurus), giant armadillo (Priodontes maximus), 40 bat species, South American tapir (Tapirus terrestris) and "boutu" or pink river-dolphin (Inia geoffrensis boliviensis). New species of fishes, amphibians, reptiles and butterflies are being described (Hanagarth, pers. comm.). Due to the abundance and visibility of many wild animals, including several crocodilians and the anaconda (Eunectes murinus), the Llanos de Mojos could be very interesting for ecotourists.

Economic assessment

The population density is c. 1.2 persons per km² in Beni Department. The indigenous population is not large and mostly in forests or near the edge of savannas. The most numerous ethnic peoples are Arawak (particularly the Baure, Trinitario and Ignaciano or Mojo), with some Tacana peoples, as well as Movima, Itonama and Chimane (cf. Añez 1992). Forest islands and gallery forests could be used for the cultivation of vanilla (Vanilla planifolia and others), for which Beni Department was once renowned. According to the 1992 national census (Presencia 1992), just 30% of the 250,000 residents of the Beni reside in the countryside and the actually rural population had decreased.

Nevertheless, the region is a major centre for beef production: 1-2 million cattle graze the native forage species. The impact of this activity seems to be patchy, as extensive areas are not populated by the cattle. Cultivated grasses facilitate the cattle-management operations and provide green forage during critical months of the dry season. Good possibilities exist to develop sustainable management for harvest of wild animals such as rhea, capybara (Hydrochaeris hydrochaeris), "lagarto" or yacaré (Caiman crocodilus yacare) and "caimán negro" or black caiman (Melanosuchus niger). Cattle and horses can be near these wild animals without substantially affecting their behaviour or reproductive biology.

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Some areas are influenced by road construction, which makes them accessible for colonization (Solomon 1989; Redford and Stearman 1989; Campos-Dudley 1992), and also may change the natural water flow and ecology of more distant plant communities. Large areas of forested land are being cleared for conversion to pasture. Exploitation for timber and fuelwood is constantly increasing, and may pose major threats to forest islands and gallery forests. The most valuable timber species, Swietenia macrophylla ("mara", bigleaf mahogany) (Forsyth 1989) and Cedrela odorata ("cedro colorado", tropical red-cedar) (Meliaceae), have been over-exploited and are becoming rare wherever accessible.

Major threats to the flora also result from overgrazing and abuse of fire as a management tool by the cattlemen. The overgrazing tends to occur near settlements. The fires sometimes get out of control and enter areas that should not be burned. Fire can eventually cause the replacement of forest by savanna. Nonetheless, plant diversity may be higher in moderately grazed and/or burned savannas. Currently, there is almost no pressure to convert natural grasslands into artificial pastures.

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There are virtually no managed protected areas for the Llanos de Mojos rich natural diversity. The ranches Elsner with Espíritu and San Rafael and the Estancia El Dorado, together some 2700 km² of wildlife reserves, are privately managed; their long-term status is not assured. The Rogaguado Lake area has been proposed as a national reserve for marsh deer (Blastocerus dichotomus), which might need over 200 km² (Montes de Oca 1989). A Decreto Supremo in 1961 declared all lakes in Beni (and Pando) departments to be national reserves (Suárez-Morales 1986), but management plans have not been elaborated or implemented.

Beni Biosphere Reserve (c. 14°30'-14°45'S and 66°00'-66°45'W), recognized in 1986, is the only functioning Biological Reserve because of the Beni Biological Station, established in 1982 (CI 1988). The 1350 km² reserve conserves 90% forest vegetation, between the Maniqui (Nuevo) and Curiraba rivers. Adjacent areas of c. 16,190 km² are committed to compatible uses (Amerindian territories; permanent production forests; Yacuma Regional Park, which is mostly private rangelands), coordinated in the Chimane Ecosystem Programme (Campos-Dudley 1992; Forsyth 1989; Redford and Stearman 1989; Walsh 1987). It is critical to determine and preserve representative savanna habitats west and north-east near this reserve, and in the other areas of the Llanos de Mojos. Across the Guaporé River to the east in Brazil (upriver from the Baures River), the Guaporé Biological Reserve near the Branco River includes 6000 km², half cerrado (IBGE and IBDF 1988).

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Map 60. Vegetation Types in the Llanos de Mojos Region, Bolivia (CPD Site SA24) (after Ribera 1992)


Añez, J. (1992). The Chimane experience in selling jatata. In Plotkin, M. and Famolare, L. (eds), Sustainable harvest and marketing of rain forest products. Island Press, Washington, D.C. Pp. 197-198.

Beck, S.G. (1983). Vegetationsökologische Grundlagen der Viehwirtschaft in den Überschwemmungs-Savannen des Río Yacuma (Departamento Beni, Bolivien). Dissertationes Bot. 80: 1-186.

Beck, S.G. (1984). Comunidades vegetales de las sabanas inundadizas en el noreste de Bolivia. Phytocoenologia 12: 321-350.

Campbell Jr., K.E., Frailey, D. and Arellano-L., J. (1985). The geology of the Río Beni: further evidence for Holocene flooding in Amazonia. Contr. Sci. Nat. Hist. Mus. Los Angeles Co. 364: 1-18.

Campos-Dudley, L. (1992). Beni: surviving the crosswinds of conservation. Américas 44(3): 6-15.

CI (Conservation International) (1988). Faces of the Beni: a visit to the biosphere reserve. Tropicus 5(winter): 4-5.

Eder, F.J. (c. 1772/1985). Breve descripción de las reducciones de Mojos. Traducción y edición de J.M. Barnadas, Cochabamba. 424 pp.

Forsyth, A. (1989). The Beni: impressions from the field. Orion (summer): 30-39.

Foster, R.B. (1989). Vegetation of the Beni. Orion (summer): 39.

Gentry, A.H. and Foster, R.B. (1981). A new Styloceras (Buxaceae) from Peru: a phytogeographic missing link. Ann. Missouri Bot. Gard. 68: 122-124.

Haase, R. and Beck, S.G. (1989). Structure and composition of savanna vegetation in northern Bolivia: a preliminary report. Brittonia 41: 80-100.

Hanagarth, W. and Sarmiento, J. (1990). Reporte preliminar sobre la geoecología de la sabana de Espíritu y sus alrededores (Llanos de Mojos, Departamento del Beni, Bolivia). Ecología en Bolivia 16: 47-75.

IBGE and IBDF (1988). Mapa de Vegetação do Brasil. Scale 1:5,000,000. Fundação Instituto Brasileiro de Geografia e Estatística (IBGE) and Instituto Brasileiro de Desenvolvimento Florestal (IBDF), Rio de Janeiro.

Montes de Oca, I. (1989). Geografía y recursos naturales de Bolivia, 2nd edition. Edit. Educacional, La Paz. 574 pp.

Moraes, M. and Beck, S.G. (1992). Diversidad florística de Bolivia. In Marconi, M. (ed.), Conservación de la diversidad biológica en Bolivia. CDC-Bolivia, La Paz. Pp. 73-111.

Parker III, T.A. (1989). Beni avifauna. Orion (summer): 35.

Parker III, T.A. and Bailey, B. (eds) (1991). A biological assessment of the Alto Madidi Region and adjacent areas of northwest Bolivia, May 18-June 15, 1990. RAP (Rapid Assessment Program) Working Papers 1. Conservation International, Washington, D.C. 108 pp.

Presencia (6 August 1992). Cuántos y quiénes somos.

Redford, K.H. and Stearman, A.M. (1989). Local peoples and the Beni Biosphere Reserve, Bolivia. Vida Silvestre Neotropical 2(1): 49-56.

Ribera, M.O. (1992). Regiones ecológicas. In Marconi, M. (ed.), Conservación de la diversidad biológica en Bolivia. CDC-Bolivia, La Paz. Pp. 9- 71.

Rioja, G. (1992). The Jatata Project: the pilot experience of Chimane empowerment. In Plotkin, M. and Famolare, L. (eds), Sustainable harvest and marketing of rain forest products. Island Press, Washington, D.C. Pp. 192-196.

Rossow, R. (1992). Boelckea, nuevo género de Scrophulariaceae de Bolivia. Parodiana 7: 15-24.

Solomon, J.C. (1989). Bolivia. In Campbell, D.G. and Hammond, H.D. (eds), Floristic inventory of tropical countries: the status of plant systematics, collections, and vegetation, plus recommendations for the future. New York Botanical Garden, Bronx. Pp. 455-463.

Suárez-Morales, O. (1986). Parques nacionales y afines de Bolivia. Academia Nacional de Ciencias de Bolivia, La Paz. 134 pp.

Walsh, J. (1987). Bolivia swaps debt for conservation. Science 237: 596-597.


This Data Sheet was written by Dr Stephan G. Beck and Mónica Moraes-R. (Universidad Mayor de San Andrés, Instituto de Ecología, Herbario Nacional de Bolivia, Correo Central - Casilla 20127, La Paz, Bolivia).

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