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Interior Dry and Mesic Forests: CPD Site SA23

SOUTH-EASTERN SANTA CRUZ
Bolivia

Location:  Centrally in South America, in south-eastern Bolivia in Department of Santa Cruz, between about latitudes 17°-20°S and longitudes 62°-58°W in provinces of Velasco, Angel Sandoval, Chiquitos, Cordillera and Germán Busch.
Area: 
c. 70,000 km².
Altitude: 
.
350-1290 m.
Vegetation: 
Transitions between phytogeographic provinces of Cerrado of central Brazil, Gran Pantanal and Gran Chaco. Mosaic of dry forests, savannas (cerrado and campo rupestre), savanna wetlands (valley-side campo and seasonally inundated savanna) and thorn scrub.
Flora: 
2000-2500 species estimated. Overall biological diversity is high; each vegetation type has a distinct flora with moderate diversity. Endemism is probably a significant component of campo-rupestre savannas, which are disjunct from similar formations of central and eastern Brazil.
Useful plants: 
For lumber, particularly decay-resistant woods; palm telephone poles; forage from numerous grass species. Amerindian uses largely unstudied.
Other values: 
Watershed protection for Paraguay River and Gran Pantanal; pre-Columbian petroglyphs; Amerindian lands; birds and other fauna; tourism.
Threats: 
Construction of natural gas pipeline and highway; unsustainable logging; poorly located mechanized soybean cultivation and cattle-ranching; mining probable.
Conservation: :
National Park, Historical Park; proposals for 3 Biological Reserves, and Forest Reserves.

Map 59: CPD Site SA23
References

Geography

South-eastern Santa Cruz is near the centre of the South American continent. There are several distinct landforms. From the region's north-west to the mid-eastern Serranía de Sunsas extends the ancient Brazilian Shield, where hilly terrain and highly weathered soils have formed from a complex of various granitic and metamorphic rocks (Oblitas and Brockmann 1978). Next southward, just to the north of the Serranía de Chiquitos and Serranía de Santiago, lies a narrow plain with a complex of soil types from sandy to loamy clays. Its western portion drains into the San Julián River, a tributary of the Amazon, whereas its eastern valley is drained by the Tucavaca River emptying into the Otuquis wetlands and so the Paraguay River. The southern portion of the region is a rolling plain with extremely sandy soils of the Gran Chaco, bordered by the seasonally inundated alluvial plain of the Upper Paraguay River and eastward by the Gran Pantanal.

In the centre of the region, several small mountain chains with almost east-west orientation provide striking contrast to the surrounding plains. The Chiquitos and Santiago ranges together extend nearly 300 km and are composed of Ordovician, Devonian and Cretaceous sandstones. Mostly they are flat-topped or table mountains having a nearly vertical southern escarpment and a steep (30°-40°) northern slope. The Serranía de Santiago is the highest topographical feature in eastern Bolivia, with maximum elevation of 1290 m on El Portón.

The climate is typical of a tropical savanna region. The mean annual temperature is 25°C (in Roboré) and c. 1000 mm of precipitation occur yearly (Navarro 1992). A pronounced dry season coincides with the southern winter. There are seasonal cold fronts ("surazos"), in June and July rarely associated with light frosts, which do not cause leaf drop in the evergreen tree species.

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Vegetation

South-eastern Santa Cruz is situated in a transition zone between the Cerrado, the Gran Pantanal and the Gran Chaco regions of central South America. The vegetation is a complex mosaic of dry forests (picture), savannas, savanna wetlands and thorn scrub correlated with local landforms (Map 59). The Serranía de Sunsas is the least studied of the areas; satellite images indicate it is covered by savanna ("cerrado") and dry forest. These rolling hills have a complicated geology, and forest is probably found on richer soils which have developed from the more easily weathered metamorphic formations. In other regions of Santa Cruz, the cerrado vegetation is found on hilltops and on the more acidic soils which have developed from granitic rocks (Killeen, Louman and Grimwood 1990).

The lower slopes of the Chiquitos and Santiago mountains are covered by forest vegetation similar in structure (and probably composition) to that on the Brazilian Shield (Navarro 1992). In the adjacent Tucavaca Valley, a distinctive closed-canopy dry forest is on the alluvial soils derived from the shield (Gentry 1993, 1994). In certain isolated locales of these areas, there is comparatively humid and evergreen forest, even with tree ferns (probably Nephelea cuspidata). The upper vegetation on the serranías varies. The western ridges (near San José de Chiquitos) are lower (to 600-800 m), more heavily eroded (not flat-topped) and covered to their crests with low forest or cerrado. In contrast, the eastern flat-topped mesetas (to 900-1157 m) of the Serranía de Santiago support open savanna reminiscent of the campo rupestre of eastern Brazil (e.g. see CPD Site SA20).

Just 50 km south of the Serranía de Chiquitos, the Gran Chaco vegetation reaches its northern (non-Andean) limit: the shift from the dry forest to thorn scrub is relatively abrupt (Navarro 1992). Soil type, as well as climate, affect the transition. South of the Serranía de Chiquitos the soils are much more sandy and the vegetation rapidly changes in structure and composition to the xerophytic deciduous forest (thorn scrub) characteristic of the Gran Chaco (CPD Site SA22).

Eastward, the Tucavaca River drains into the Bañados de Otuquis which are contiguous to the east with the Gran Pantanal wetlands. In this Bolivian portion one finds a rich mosaic of vegetation types according to different levels of inundation and/or the duration of seasonal dryness. Characteristic for much of this wetland complex is the palm Copernicia alba. Palm savannas ("palmares") also occur north-west of San José de Chiquitos where meandering watercourses flow into Lake Concepción.

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Flora

Little is known about the flora of this region. For bordering regions only two incomplete checklists and several descriptions of vegetation have been published (Cárdenas 1951; Prance and Schaller 1982; Killeen and Nee 1991; Killeen, Louman and Grimwood 1990; Spichiger et al. 1991; Ramella and Spichiger 1989). Botanical collecting expeditions, such as those organized by A. Orbigny (1834-1847), T. Herzog (1907), M. Cárdenas (1950), D. Daly (1983) and Conservation International's Rapid Assessment Program (1991) (see Parker et al. 1993) have resulted in many interesting specimens including recently discovered probably undescribed species, especially from the campo-rupestre savannas of the Serranía de Santiago.

Those open savannas are dominated by Gramineae; important also are herbaceous or subshrub species in Cyperaceae, Leguminosae, Compositae, Polygalaceae, Melastomataceae and Rubiaceae. Although not abundant, species in Velloziaceae, Xyridaceae and Eriocaulaceae occur. The grass flora is better investigated and indicates strong similarities with campo rupestre, having some of its characteristic species: Axonopus brasiliensis, Paspalum gardnerianum, P. pectinatum, P. polyphyllum and Sporobolus sprengelii (Killeen 1990).

The floras of the other vegetation types also are poorly known, but are assumed to be similar to the better studied floras in Bolivia and Brazil (Cerrado, dry forest, Gran Pantanal) and Paraguay and Argentina (Gran Chaco) (see CPD Sites SA21 and SA22). Yet Gentry (1993, 1994) found the dry forest in the Tucavaca Valley to be one of the most diverse in the neotropics (97 species over 2.5 cm dbh in 0.1 ha). Several taxa believed to be only in southern Brazil were relatively abundant; endemics also were important.

Due to the lack of even a preliminary checklist for south-eastern Santa Cruz, the amount of endemism is unknown. The only published endemics are Frailea chiquitana (Cactaceae) and Axonopus herzogii (Gramineae), but likely new species have been found in Norantea (Marcgraviaceae), Palicourea (Rubiaceae) and Andropogon and Anthaenantiopsis (Gramineae).

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Useful plants

Much of the region is sparsely populated by indigenous peoples (Chiquitano to the north, Ayoreo near the Serranía de Santiago, and Guaraní to the south-west), who have a rich heritage of using native plants. This usage is largely undocumented and their Westernization is proceeding rapidly. Much of this knowledge will be lost with the adult generation unless ethnobotanical studies are undertaken.

Copernicia alba palms are used to make telephone poles. Plants of the region in the national economy are timber and forage resources. Timber harvest had been selective and non-intensive (e.g. for the decay-resistant woods of Astronium spp., Schinopsis spp. and Tabebuia spp.), while grazing and browsing of natural vegetation by cattle have been extensive.

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Social and environmental values

Indigenous peoples still are surviving with their traditional ways. The general region has broad potential attractiveness, offering the large Lake Concepción to its north, the scenic beauty of different serranías along with the regional highpoint, and the diversity of plants and animals, with cultural interests of pre-Columbian petroglyphs and recently restored Jesuit missions. Bird watchers are quite drawn to the mosaic Bañados de Otuquis and adjacent Gran Pantanal wetlands. An inexpensive railroad makes the region accessible to tourists from neighbouring regions. The vegetation and wetlands also provide catchment protection for the Upper Paraguay River and the Gran Pantanal.

This region covers a vast area within which is the southern end of the East Bolivian lowlands Endemic Bird Area (EBA B36). This is one of the least ornithologically known areas in Bolivia. The only restricted-range species of the EBA that definitely occurs in this region is the buff-bellied hermit (Phaethornis subochraceus).

Economic assessment

The antiquated railroad traversing the region roughly parallels the serranías (Map 59). This transportation system makes the region accessible to many Bolivian nationals and others who depend on low-cost methods of access. An imminent modern highway to Brazil will stimulate overall development.

Shifting agriculture by indigenous groups continues to be limited to restricted areas. Sustainable development would be similar to traditional land-use patterns that have occurred over the 250 years since settlement by Jesuit missionaries. Although cattle-ranching is suitable for many of the forest soils in South-eastern Santa Cruz, rotational grazing needs to be encouraged to improve the productivity of native species. Native vegetation could be supplemented by limited planting of cultivated forage grasses. Moreover, given the last decade's more intensive logging practices, modern forestry methods need to be employed to ensure the long-term productivity of the hardwoods.

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Threats

In Santa Cruz Department (excluding the Gran Chaco vegetation), 17% of the forested area had been converted to cultivation and cattle-ranching by 1991: 13,759 km²; the yearly deforestation is 329 km² (based on 1985 and 1990 satellite images). Almost all forest is gone near the capital Santa Cruz de la Sierra in the Andean piedmont, but less than 1% had been deforested in South-eastern Santa Cruz (in the 1990 images).

The principal threat to the biological diversity of the region is expansion of the booming mechanized agricultural economy from central Santa Cruz Department. The local government and international agencies are promoting cultivation of soybeans (Glycine soja) on the central plain of Santa Cruz, where fertile alluvial soils can be used over the long term. Unfortunately, indiscriminate general expansion of mechanized agriculture is resulting in environmental degradation due to inappropriate land use in adjacent areas.

The perception that the alluvial soils of the Tucavaca Valley are fertile has brought that area to the attention of investors. However, most of its soils are unsuited for mechanized agriculture because they are either too sandy or have subsoil clay hardpans. Nevertheless, speculators are purchasing land or obtaining governmental land at low cost through the Bolivian land-reform system.

Agricultural development in Santa Cruz also occurs from intensive cattle-raising operations using cultivated grasses and legumes. These operations can be viable over the long term with use of the appropriate soil types, and proper management techniques (Killeen 1991). Operations that attempt soybean cultivation might change eventually to cattle production, but probably after substantial damage has been done to the soil resources.

Two separate, major development projects are driving agricultural expansion eastward from the central plain into this region: construction of a modern highway to link Bolivia and Brazil, and construction of a natural gas pipeline between the Bolivian gas fields and the industrialized states of Brazil, scheduled for 1993-1994. The pipeline project will require an extensive road network for its construction, operation and maintenance. Unfortunately, the highway has been proposed to be approximately 40 km north of the railroad on the opposite, northern side of the Serranía de Santiago where it would extend through the Tucavaca Valley; conversely, the pipeline system would be approximately 40 km south of the railroad. If financing for these two separate projects is approved without broadened environmental consideration, significant damage will occur needlessly.

Important mining initiatives probably will take place by 1998 scattered throughout the Bolivian portion of the Brazilian Shield (C. Brockmann, pers. comm.). Semi-precious stones are widely found; north-west of the Serranía de Sunsas modern bulk gold mining is in operation; and world-class iron-ore deposits have been found near Santo Corazón and 25 km south of Puerto Suárez (at Mutún). Claims have been filed for rights to the subsoil minerals in the geologically complex Serranía de Sunsas, which has ultramafic rock formations: platinum, copper, manganese, nickel and other minerals are likely to be discovered in commercially suitable deposits.

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Conservation

Separate environmental impact studies of the highway and the pipeline projects were made, without considering the synergistic effects of the two works, or the construction of them in the same region at the same time. Combining the projects and placing them within the existing developed corridor surrounding the railroad right-of-way would appreciably decrease their negative environmental effects.

Bolivia is making genuine efforts to conserve a substantial portion of its biological resources and recently formed a Sistema Nacional de Areas Protegidas (SNAP). Recent actions provide confidence that protected areas will be established in South-eastern Santa Cruz. Three basic areas (updated below) had been recommended for designation as conservation units by Navarro (1992) and the Gran Chaco is one of nine priority areas in Bolivia identified by the Global Environment Facility (GEF) for conservation. Although all the recommendations of Navarro (1992) would bring some 25% of Santa Cruz Department into SNAP (the National System of Protected Areas), land uses would differ - within many of his basic areas there are even developed localities: e.g. places settled with cattlemen or farmers, or the railroad corridor extending across the recommended Serranía de Santiago-Otuquis National Park.

Environmental organizations are working with scientists and government authorities to determine exact boundaries and additional areas for conservation, and the appropriate protective status for each area. Agricultural and timber interests work toward limiting the size of proposed reserves. Santa Cruz Department has the double distinction of leading the country in deforestation, but as well in the creation of functioning National Parks and wildlife reserves.

In the north-east (see Map 59 area 1), a San Matías Biological Reserve would incorporate an altitudinal transect extending from cerrado savanna and dry forest to inundated marsh and forest of the Gran Pantanal. In Brazil farther east are the Taiamã Ecological Station (112 km²) and the Mato Grosso Pantanal National Park (1350 km²) (IBGE and IBDF 1988). In south-east Santa Cruz (Map 59 areas 2 and 3), Santiago de Chiquitos and Otuquis-Pantanal Biological Reserves would contain portions of the Serranía de Sunsas, the Tucavaca Valley, the Serranía de Santiago and the Bañados de Otuquis. In the south-west (Map 59 area 4), the recently established Kaa-lya National Park includes the northern part of the Gran Chaco, the Serranía de Chiquitos and the Bañados de Izozog. Near this park and San José de Chiquitos is Santa Cruz la Vieja Historic National Park (c. 170 km²) (Map 59 area 5), which was the region's only protected area (although unmanaged), with dry-forest vegetation and archaeological ruins from the 1600s.

Bolivia contains more intact dry forest (sometimes called semi-deciduous forest) than any other Latin American country (Parker et al. 1993). However, no protected area in Bolivia encompassed a substantial portion, and insufficient dry forest has been planned for protection. Even though a substantial portion has become private holdings, much of the c. 40,000 km² of dry-forest formation in eastern Santa Cruz Department is still intact, and about half of this poorly studied formation is in south-eastern Santa Cruz. Some 2000-3000 km² of dry forest have been recommended for protection, mainly in the San Matías Biological Reserve. Most of the land between the three recommended protected areas and the new National Park has been recommended for incorporation into a series of Forest Reserves (Navarro 1992). However, no governmental action has been taken and these forests are being exploited without a sustainable management plan.

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Map 59. South-eastern Santa Cruz, Bolivia (CPD Site SA23)

References

Cárdenas, M. (1951). Un viaje botánico por la Provincia Chiquitos del oriente boliviano. Revista Agric. (Cochabamba) 7(6): 3-17.

Gentry, A.H. (1993). Dry forest vegetation and phytogeography in the Tucavaca Valley. In Parker III, T.A., Gentry, A.H., Foster, R.B., Emmons, L.H. and Remsen Jr., J.V., The lowland dry forests of Santa Cruz, Bolivia. RAP Working Pap. 4, CI, Washington, D.C. Pp. 40-42.

Gentry, A.H. (1994). A new South American vegetation type: the conservational significance of the dry forest of Santa Cruz, Bolivia. Manuscript.

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.

Killeen, T.J. (1990). The grasses of Chiquitanía, Santa Cruz, Bolivia. Ann. Missouri Bot. Gard. 77: 125-201.

Killeen, T.J. (1991). Range management and land-use practices in Chiquitanía, Santa Cruz, Bolivia. Rangelands 13: 73-77.

Killeen, T.J., Louman, B.T. and Grimwood, T. (1990). La ecología paisajística de la región de Concepción y Lomerio en la Provincia Nuflo de Chávez, Santa Cruz, Bolivia. Ecología en Bolivia 16: 1-46.

Killeen, T.J. and Nee, M. (1991). Catálogo de las plantas sabaneras de Concepción, Depto. Santa Cruz, Bolivia. Ecología en Bolivia 17: 53-71.

Navarro-S., G. (1992). Estudio de parques nacionales y otras áreas protegidas (borrador final). Proyecto de Protección de Los Recursos Naturales en el Departmento de Santa Cruz (Componente Proyecto Tierras Bajas). Corp. Regional de Desarrollo de Santa Cruz (CORDECRUZ)-KFW-Consorcio IP/SCD/KWC, Santa Cruz. 96 pp.

Oblitas-G., J. and Brockmann-H., C.E. (1978). Mapa geológico de Bolivia. Servicio Geológico de Bolivia (GEOBOL) and Yacimientos Petrolíferos Fiscales de Bolivia (YPFB), La Paz.

Parker III, T.A., Gentry, A.H., Foster, R.B., Emmons, L.H. and Remsen Jr., J.V. (1993). The lowland dry forests of Santa Cruz, Bolivia: a global conservation priority. RAP (Rapid Assessment Program) Working Papers 4, Conservation International (CI), Washington, D.C. 104 pp.

Prance, G.T. and Schaller, G.B. (1982). Preliminary study on some vegetation types of the Pantanal, Mato Grosso, Brazil. Brittonia 34: 224-251.

Ramella, L. and Spichiger, R. (1989). Interpretación preliminar del medio físico y de la vegetación del Chaco Boreal. Contribución al estudio de la flora y de la vegetación del Chaco. I. Candollea 44: 640-680.

Spichiger, R., Ramella, L., Palese, R. and Mereles, F. (1991). Proposición de leyenda para la cartografía de las formaciones vegetales del Chaco paraguayo. Contribución al estudio de la flora y de la vegetación del Chaco. III. Candollea 46: 542-564.

Author

This Data Sheet was written by Dr Timothy J. Killeen (Museo de Historia Natural Noel Kempff Mercado, Casilla 2489, Av. Irala 565, Casilla 2489, Santa Cruz, Bolivia and Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A.).

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