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Central South America: Northern Bolivia

The Beni savannas, also known as the Moxos plains, are the third largest complexes of savannas in South America. This ecoregion has been identified as a plant diversity and endemic center. The abundance of fauna and flora, including threatened species, makes this region highly valuable.

  • Scientific Code
    (NT0702)
  • Ecoregion Category
    Neotropical
  • Size
    48,700 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
The Beni savannas are located in the lowlands of the southwestern Amazon basin, extending northeastward from the foot of the Andean ranges. Almost all of the ecoregion lies within Bolivia in the departments of El Beni, Cochabamba, La Paz, Pando, and Santa Cruz, with small areas along the Iténez (Guaporé) River in the Brazilian State of Rondonia and in the Pampas del Heath of the Madre de Dios Department of Peru. This ecoregion comprises seasonal savannas and wetlands with forest islands and gallery forests on poorly drained Quaternary alluvial bottomlands with a marked dry season and flooding in the wet season. The plains form a complex mosaic of humid seasonal forest in a matrix of seasonal savanna where annual flooding and fire are the most important ecological factors. The region is traversed by three major rivers, the Beni in the west, the Iténez or Guaporé to the east, and the Mamoré in the central region. These rivers converge to form the Madeira River, the major southern tributary of the Amazon River. .

The plains lie between 130 and 235 m in elevation; however, local relief is typically on the order of 2-6 m. The rivers flood each year during the humid season between December and May as a result of high rainfall and snowmelt in the Andes. The flooding covers from 50 to 60 percent of the land for a period of four to ten months. Ponding of rainwater also contributes to the seasonal flooding of many areas that are more distant from the active rivers. Rainfall ranges from 1,300 mm per year in the east of the region to 2,000 mm in the west. The average annual temperature is 25° C , with daily highs frequently on the order of 35-37°C. During the austral winter, occasional cold fronts penetrate from the south, causing temperatures to drop to as low as 6-10°C for brief periods.

The landscape elements in this region include rivers, lakes, permanent swamps and marshes, terrain inundated for up to ten months (bajíos), terrain inundated for four months of the year (semialturas), and uplands (alturas) that flood only briefly or not at all. A globally-unique feature of the Llanos de Moxos is the presence of numerous shallow, flat-bottomed, oriented lakes. Somewhat similar lakes occur in the Pantanal, but are unknown from any other portion of the Amazon basin. Another outstanding characteristic of the Llanos de Moxos ecoregion is the presence of thousands of archaeological earthworks created by the diverse indigenous cultures (Denevan 1966, Mann 2000). These features include raised agricultural fields, mounds, platforms, causeways, dikes, canals, and even fish weirs (Erickson 2000). These earthworks influence the distribution of forest, savanna, and wetland in the modern landscape.

The flora and fauna of the region are influenced by the Amazon, the Chaco, and the Cerrado-Pantanal biogeographic regions. An estimated 1,500 vascular plant species are found on these savannas, probably few of which are endemic . Vegetation types vary primarily with the amount of flooding, soil type, elevation, and fire regimes. The influence of livestock grazing is another important factor.

Herbaceous formations are the most widespread landscape elements of the Beni savannas, occupying expansive low areas with from four to ten months of inundation. These areas are dominated by sedges and grasses such as Cyperus giganteus, Eleocharis geniculata, Rhynchospora trispicata, Hymenachne spp., Leersia hexandra, Luziola peruviana, Paspalum acuminatum Setaria sp., and other herbaceous plants including Eichhornia spp., Hydrocotyle sp., Ludwigia spp., Nymphaea spp., Pontederia spp., and Thalia geniculata) . On the higher zones, the grassland is dominated by grasses, such as Andropogon bicornis, Paspalum laxum, and Sporobolus spp. Two vegetation associations are characteristic on the treeless northwestern section which is situated upon acidic soils: Anthaenantia lanata, Trachypogon polymorphus, and Macairea scabra shrub with a groundlayer of Mesosetum penicillatum and Bulbostylis juncoides .

The tree and shrub mosaic comprises several types. On the more shallowly flooded savannas, where single trees dot the savanna, tree height ranges from 4 to 7 m. The most abundant species are fire tolerant species such as Copernicia alba, Tabebuia aurea and T. heptaphylla, Machaerium hirtum, and Pseudobombax marginatum and P. longiflorum. Termite mound savannas are locally important on the higher areas, where seasonal flooding is shallow or intermittent. Typical mound elements include the cactus Cereus braunii, Celtis spp., Coccoloba spp., Copernicia alba, Cordia spp., Genipa americana, Geoffroea striata, Inga spp., Tabebuia heptaphylla, Sorocea spruceii, and Xylosma venosum. Woody species in the better drained savannas and woodlands include Tabebuia ochracea, Luehea paniculata, Acacia albicorticata, Acrocomia aculeata, Astronium fraxinifolium, Cordia glabrata, Pithecellobium scalare, Pseudobombax marginatum, and Samanea tubulosa . A unique element of the woodlands and savannas is Piptadenia robusta, a tree that until 1994 had been identified only from the savannas of Venezuela. Curatella americana, a widespread element of Neotropical savannas, is not found in the more nutrient rich flooded savannas, but rather is restricted to better-drained, nutrient-poor savannas, typically where there are lateritic surfaces, termite mounds, or archaeological raised fields. A unique edaphic association is found where salt accumulations occur at the surface in zones of internal drainage, where Machaerium hirtum, Copernicia alba, and Panicum laxum are the dominants.

A characteristic landscape element of the Beni savannas ecoregion are the forest islands in the savannas and wetlands. These features are isolated stands of trees upon low relief features, primarily natural levee remnants, ant and termite mounds, and archaeological earthworks. These islands include trees such as Attalea phalerata, Ceiba spp., Coccoloba spp., Ficus spp., Genipa americana, Guarea spp., Rheedia spp., Salacia spp., Trichilia spp., Myristica sebifera, Sterculia apetala, and Vitex cymosa. Lower islands upon clayey substrates contain species typical of the semialturas such as Copernicia alba, Guazuma ulmifolia, and Celtis spp., as well as Ficus spp. Most species of the forest islands are dispersed by birds and mammals, followed in importance by water-dispersed species. Wind dispersed species are typically uncommon in the forest islands. The forests may expand outward as fire and floods allow. The forest islands provide critical habitats for many species of plants and animals, including the nesting sites for the endemic blue-throated macaw.

The larger rivers are bordered by forests upon active meander belts subject to intense lateral erosion and deposition during the annual floods, which inundate the landscape in a swath up to 10 km in width. These flooded forests and swamp forests are characterized by a low canopy (15 to 20 m in height) and a lesser species richness with greater dominance of several species, relative to more stable upland forests. The areas of primary succession are represented predominantly by herbaceous and shrub pioneer species such as Tessaria integrifolia, Gynerium sagittatum, and Salix humboldtiana, and by trees such as Cecropia spp., Pourouma spp., Erythrina poeppigiana, Sapium marmieri, and Ochroma pyramidalis. On the best-drained former alluvial terraces (uplands), expansive dense humid tropical forests are found with a canopy 40 m or more. These terraces have the highest arboreal species diversity in the region, including valuable hardwood species such as the endangered mahogony (Swietenia macrophylla). . It should be noted that the major riverine forests (e.g., those of the Beni, Mamoré, and Iténez/Guaporé rivers) are included in the Southwest Amazon Moist Forest Ecoregion, not the Beni savannas.

Along the many smaller rivers of the region, there are forests upon less active natural levee and backslope surfaces. Arboreal palms have a strong presence in the forests including Attalea phalerata, Astrocaryum murumuru var. macrocalyx, and Syagrus sancona. Bactris major is locally important as an understory palm. The dicot trees of the forests are a mix of evergreen and deciduous species from distinct biogeographical provenances. Typical Amazonian riverine forest species include Calycophyllum spruceanum, Calophyllum brasiliense, Ceiba pentandra, Genipa americana, Hura crepitans, and Vitex cymosa. Amazonian upland elements include Acacia polyphylla, Ampelocera ruizii, and Cordia nodosa. Deciduous seasonal or dry forest elements include Anadenanthera macrocarpa, Chorisia spp., Cordia alliodora, Enterolobium contortisiliquum, Gallesia integrifolia, Guazuma ulmifolia, Maclura tinctoria, Spondias mombin, and Triplaris boliviana. Large Ficus spp. are abundant in the forests of the Beni savannas and are critical resources for many vertebrates.

In the largely unexplored palm savannas and palm swamps, primarily east of the Mamoré River, pure stands of Euterpe sp., Copernicia alba, Mauritia flexuosa or Mauritiella aculeata are common, each in unique ecological settings.

Biodiversity Features
The ecoregion has a diverse flora. There are approximately 1500 species of plants in the savannas, and 5000 species in the forests in the Chimane Ecosystem area of the Beni Biosphere Reserve. The research in the area resulted in the discovery of 6-8 new species: Boelckea (a new genus of Scrophulariaceae), Bellucia (Melastomataceae), Casimirella (Icacinaceae), Lantana (Verbenaceae) Peltodon (Labiatae), Wolfiella (Lemnaceae) and Andropogon (Graminae). The number of endemic plants is unknown, and likely to be low (Beck and Moraes 1997).

In this region, 146 mammals have been reported. The rivers are home to abundant boto river dolphins (Inia geoffrensis). Some Chaco-Cerrado elements include marsh deer (Blastocerus dichotomus) and maned wolves (Chrysocyon brachyurus) which reach their northwesternmost range here in the Pampas del Heath. Giant river otters (Pteronura brasiliensis) are considered locally extinct. Pumas (Puma concolor), jaguars (Panthera onca), jaguarundis (Herpailurus yagouaroundi) and other cats are still locally common in the region. Various mammals that occur here and are not found elsewhere in Amazonia include the marsh deer, maned wolf, central South American seasonal forest primates (Alouatta caraya, Aotus azarai, Callicebus donacophilus, C. modestus, C. olallae, and Callithrix melanura), rodents (Akodon dayi, Kunsia tomentosus, and Oxymycterus inca), four species of opossums (Monodelphis kunsi, Marmosops dorothea, Lutreolina crassicaudata, and Gracilinanus agilis), various bats (Vampyrum spectrum, Phyllostomus hastatus, and Micronycteris behnii, and several species of Platyrrhinus, Molossops temminckii).

Fully 509 species of birds have been recorded in this area. The Beni savannas contain a unique assemblage of biota found together in no other single ecoregion of South America: nowhere else on Earth is it possible to find Inia, Rhea, Blastocerus, and Chrysocyon. The Llanos of the Orinoco do not contain Melanosuchus, Rhea, Blastocerus,or Chrysocyon. While the Pantanal ecoregion shares many taxa with the Llanos de Moxos, it does not include Inia or Melanosuchus. Species that occur only here or in only a few other places in Amazonia include white-bellied nothuras (Nothura boraquira), greater rheas (Rhea americana), southern screamers (Chauna torquata), plumbeous ibis (Theristicus caerulescens), crowned eagles (Harpyhaliaetus coronatus), long-tailed ground-doves (Uropelia campestris), golden-collared macaws (Ara auricollis), monk parakeets (Myiopsitta monachus), and burrowing owls (Athene cunicularia). The most notable bird of the Llanos de Moxos is the endangered blue-throated macaw (Ara glaucogularis), a forest island specialist that feeds primarily on the fruits of Attalea and Acrocomia palms and which occurs nowhere else on Earth. This macaw has an estimated wild population of <1,000 and its entire range is within cattle ranches.

Reptiles, amphibians, and fish are important elements of the savannas, wetlands, lakes, and rivers. The endangered black caiman (Melanosuchus niger) and river turtles (Podocnemis expansa) have important populations the Beni savannas, along with the abundant yacare caiman (Caiman yacare), anacondas (Eunectes murinus), and false water cobras (Hydrodynastes gigas). Common lizards include tegus (Tupinambis teguixin), ameivas (Ameiva ameiva loeta), skinks (Mabuya frenata), and species of the genus Tropidurus. The legless anguid lizard Ophiodes intermedius is a species of the humid Chaco and the Pampas, and is not found elsewhere in the Amazon. Likewise, Tropidurus etheridgei is a species of the semiarid Chaco. Typical amphibians include giant rococo toads (Bufo paracnemis), arrow poison frogs (Epipedobates pictus), and marsh frogs (Lysapsus limellus). The herpetofauna of the Beni savannas remains poorly known, but preliminary studies at the Beni Biological Station have revealed the highest anuran diversity from a Neotropical savanna (Reichle 1997). Over 325 species of fish are known from the Mamoré river drainage alone, many likely remain undescribed from other areas. The seasonally-flooded savannas and forests are important habitats for fish important to the diets of people of Amazonia such as pacú (Colossoma macropomum), sábalo (Prochilodus nigricans), and surubí (Pseudoplatystoma spp.). The savannas themeselves are home to abundant fish such as bentón (Hoplias malabaricus), buchere (Lepthoplosternum beni), and yeyú (Hoplerythrinus unitaeniatus) which support vast numbers of wetland birds.

Current Status
Since the arrival of the Jesuits in the 1680s, the predominant land use of the Llanos de Moxos ecoregion has been cattle ranching on the savannas and wetlands. Anthropogenic fire is used to remove low quality biomass and stimulate regrowth at the end of the dry season. Consequently, few areas remain in their pre-European state. Some forest islands are actually remaining fragments from a previously larger forest stand reduced by human activities; however, historical deforestation in the Moxos region has not yet approached the extent in neighboring regions.

Beni savannas and wetland areas are poorly represented in Bolivia’s protected areas system. The Alto Madidi National Park contains areas of these savannas in the north of the La Paz Department. The Manuripi-Heath National Amazonian Reserve of La Paz and Pando contains small islands of savanna. The Beni Biological Station is a UNESCO Biosphere Reserve located in the southwest of this region. It includes 1,350 km2 of flat lowlands, but with little savanna. The Iténez Fiscal Reserve of 15,000 km2 is located on the eastern extreme, but only partially in the Llanos de Moxos ecoregion. Timber extraction is the main activity in this reserve. A national park has been proposed for the savannas and Mauritia palm swamps to the south of the Iténez Fiscal Reserve. A large portion of the southern savannas and wetlands are located with the Multi-ethnic Indigenous Territory and the Isiboro-Sécure Indigenous Territory/National Park. Land tenure and management issues in these territories, however, remain uncertain. The Sirionó Indigenous Territory occupies a portion of the forest-savanna mosaic approximately 60 km east of the Mamoré River. The Ríos Blanco and Negro Wildlife Reserve in Santa Cruz contains a portions of the southern Baures savannas and wetlands. In Peru, the all of the Pampas del Heath are protected by the Bahuaja Sonene National Park.

Types and Severity of Threats
Much of the Beni savannas is subject to extensive grazing pressure by cattle and subject to intense seasonal burning for forage maintenance, particularly in the central and southern areas Uncontrolled burns threaten the natural communities. The floristic composition and structure and the bird communities have been heavily impacted by these activities . High levels of trampling, manuring, and browsing by cattle is documented to lead to the denudation of forest islands (Langstroth 1996). Additional deterioration of the forest islands and savanna woodlands is locally severe due to extraction of Tabebuia heptaphylla, Copernicia alba, and other trees to construct corrals and fences. Irrigation of pastures using water from the rivers and draining of wetlands are changing the ecological characteristics of the region.

Human population growth increases the hunting pressure on local fauna . The road network in the Moxos plains is still poorly developed. Access is possible from La Paz with roads connecting to Riberalta/Guayaramerín to the north and Trinidad to the east. From Trinidad, an asphalt road now provides access from Santa Cruz. Smallholder ranchers and agriculturists have settled along these roads.

Human settlements are generally restricted to the limited better-drained portions of the landscape where the annual floods are least significant. These areas are primarily upon palaeofluvial or archaeological relief features. Swidden agriculture is widely practiced in the gallery forests and larger forest islands. The extraction of trees for pulp constitutes a major new threat to the gallery forest habitats .

The seasonally flooded savannas are largely not farmed presently. Indigenous peoples of the region, however, once practiced farming upon artificial raised fields in the savannas. Nevertheless, the conversion of large tracts of the landscape to commercial agriculture, is an ever-present threat. Under increasing demographic pressure and economic uncertainty of livestock production, a shift from semi-natural rangelands to fields of rice, sugar cane, and soybeans is not unforeseeable.

Despite much improvement over the past three decades, poaching of endangered wildlife species for illegal trade of hides and skins is still a problem in the absence of species management plans and enforcement of laws.

Justification of Ecoregion Delineation
The Beni savannas ecoregion is a clearly delineated physical, cultural, and biogeographical region. It is easily discernable from space as a distinct region of the southernmost Amazon basin. It is easily defined as the region of savannas and wetlands occupying the upper watershed of the Madeira River, comprised by the watersheds of the Beni, Mamoré, and Iténez (Guaporé) rivers. While it is a region low in endemicity, its biota is globally unique in terms of the commingling of elements from diverse biogeographic realms. This ecoregion has received very little attention from the conservation community generally, in part due to a lack of familiarity with its characteristics and global significance. It is certainly no less unique or valuable than its analogues, the Pantanal or the Florida Everglades. In addition to its biological values, the Beni savannas ecoregion is one of the greatest examples of an archaeological cultural landscape known (Mann 2000). The present-day landscapes are a fascinating product of a rich history of human, biological, and geomorphological interactions. This region is distinct from the surrounding moist forests by the lack of continuous tree cover and the dominance of savanna species associations. Linework follow Ribera et al. (1994) by lumping the following components of their vegetation classification – "Beni plains": "Moxos humid savannas", "Amazonian savannas", "Magdalena wetlands", and portions of "riparian forests with mayor erosion activity". These extensive savannas and wetlands offer important refuge and wintering grounds to many migrant waterfowl, and are host to a number of endemic species.

References
Beck, Stephan G., and Monica Moraes. 1997. Llanos de Mojos Region, Bolivia. S. D. Davis, V.H. Heywood, O. Herrera-MacBryde, J. Villa-Lobos and A.C. Hamilton, editors. Centres of plant diversity: A guide and strategy for their Conservation, 3 The Americas. WWF, IUCN, Oxford, U.K.

Prepared by: Robin Sears and Robert Langstroth
Reviewed by: In progress

 

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