The Guarani Indians initially described this region as "Gran Chaco", which implies productive hunting grounds. Today much of the northern Chaco is still abundant with large game mammals, suggesting sustainably harvested populations. However, this is no longer the case in much of the southern Chaco where rampant overgrazing and human population growth has preceded the pristine nature of the Chaco. An important migration route, many species of avifauna can be found in this ecoregion throughout the year. More protected areas are needed in order to save this habitat from overwhelming agricultural development.
Location and General Description
The Chaco ecoregion as defined herein is generally restricted to the northwestern two-thirds of western Paraguay, and east of the Andes in southeastern Bolivia and northwestern Argentina. The northern boundary in general falls just west of the center of the continent. The northern, southern, western and eastern boundaries of this ecoregion terminate approximately at the 170 and 310 south latitudes and 650 and 560 west longitudes, respectively. Mean annual temperature in the central Paraguayan Chaco during 1989-1990 was 26°C with monthly means ranging 18.60 - 33.7°C , and annual rainfall was 865 millimeters (mm) (mean = 72 mm/month) with monthly means ranging 10 – 164 mm. Most scientists agree that the Chaco formed during Pleistocene postglacial fluctuations, from an arid to humid to semiarid environment, as initially proposed by Lüders.
The Chaco is comprised of several habitats, although savannas, thorn forests, or a transition of these two predominant. Savanna and grassland habitats are characterized by a high abundance of grasses. Quebracho woodland is more open than thorn forest, and is characterized by thorny bushes (e.g., Prosopis sp.), shrubs, and cacti (e.g., Opuntia sp.), with scattered trees (e.g., Aspidosperma quebracho, Bulnesia sarmientii and Schinopsis sp.) up to 13 meters (m) high. Dominant species include Prosopis ruscifolia, a thorny legume, and Opuntia sp. cactus. Isolated tracts of thick, impenetrable primary thorn forest are sometimes left when land is cleared for agrarian purposes. The understory of primary thorn forest is punctuated with spiny terrestrial plants such as bayonet bromeliads (Bromelia serra) and star cactus (Cleistocactus baumanii). The Chaco is punctuated "tajamars" (ponds made by ranchers for cattle) that support some aquatic life.
The Chaco represents a region that was inadequately explored until recently, with new species of large vertebrates such as the Chacoan Peccary (Catagonus wagneri) being discovered as recently as the 1970’s. Moreover, new records of known species are increasingly documented as the international scientific community realizes more fieldwork-hours.
The Chacoan Peccary (Catagonus wagneri), discovered in the 1970’s, is undoubtedly the most famous Chacoan (if not continental) endemic. Armadillos reach their peak diversity in the Chaco, with at least eight and ten species in the Paraguayan, and Argentinean Chaco, respectively.
Other important species include the following: lesser mara (Pediolagus salinicola), giant tuco-tuco (Ctenomys conoveri); greater rhea (Rhea americana), brushland tinamou (Nothoprocta cinerascens), chaco chachalaca (Ortalis canicollis), black-legged serieman (Chunga burmeisteri), chaco blue-fronted amazon (Amazona aestiva), picui Ground Dove (Columbina picui), Guira Cuckoo (Guira guira), Little Thornbird (Phacellodomus sibilatrix), many-colored chaco finch (Saltaitricula multicolor); paraguayan caiman (Caiman yacare), southern boa (Boa constrictor occidentalis), false water cobra (Hydronastes gigas), horned frog (Ceratophrys sp.), argentine walking frog (Phyllomedusa sauvageii).
Due to its central location in South America, the Chaco harbors migrant birds from both southern (Austral) and northern (Neotropical) regions of South America, as well as migrants from even further north in North America.
The relatively newly established Parque Nacional (PN) Kaa-Iya, in Bolivia, sits abreast the Paraguayan border, relatively close to PN Defensores del Chaco. National Parks exist in the northern (PN Defensores del Chaco) and western sections of the Paraguayan Chaco, as well as several private reserves, including one each in the central (Estancia Boquerón'í) and northwestern (Estancia de South American Ltd.) Paraguayan Chaco. Argentina also has several reserves in the Chaco, primarily in the northern Argentine Chaco (RN Formosa, PNs Pilcomayo, Baritú, Callilegua, El Rey, and RPs Agua Dulce, Potreros de Yala, El Bagual), with a couple in the central (RP Los Palmares and RP Copo) and southern (RP Chaco) regions.
Reserves in the eastern Paraguayan Chaco and western Bolivian Chaco are noticably lacking, and reserves in the central and southern Argentinean Chaco are scant. A series of corridors connecting existing reserves would be ideal. Additionally, it is important to insure that these reserves are all properly staff, with the personnel well trained in law enforcement and habitat/wildlife management. Perhaps the main threat to the few pristine regions of the Chaco is increased development, which should be dampened wherever possible.
Types and Severity of Threats
Much of the Chaco is in various stages of alteration due to grazing of cattle and goats, the latter especially in the southern Chaco. This development is perhaps least severe around the border of the Paraguayan and Bolivian Chaco, and most extensive in the Argentinean Chaco. Paved road development projects provide easy access to remote sites to hunt game and alter pristine wilderness for agrarian development. A good example of this is the Trans-Chaco highway that connects Paraguay and Bolivia (completed in late 1990s).
Justification of Ecoregion Delineation
Within Argentina, delineation’s for the chaco were derived from Daniele and Natenzon, and linework follows their Bosques y Arbustales del Chaco Semiárido region. Other resources consulted include Cabrera and Morello. Within Bolivia, we followed Ribera et al. Our linework encompasses their broad classification of the "chaco plains", with the following components included: "chaco dry forests", "chaco matorral and xeric scrub", "sandy lowlands", and the "Izozog wetlands". Finally, in Paraguay we referred to the UNESCO map (1980) for representation, and linework follows their classification of Drought Deciduous Lowlands (and submontane) Woodland – specifically in the province of Chaco, Paraguay, between the plains of the Paraguay and the Parana Rivers. The chaco region is recognized internationally as unique and needs no justification. We have divided the greater "chaco" into mainly climatic components, to include this Chaco ecoregion and also the Humid Chaco and Arid Chaco ecoregions.
Additional information on this ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
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- Brooks, D. M. 1992. Reproductive behavior and development of the young of the Chacoan peccary (Catagonus wagneri Rusconi, 1930) in the Paraguayan Chaco. Z. Sauget. 57:316-317.
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