Boundaries

This ecoregion contains the endorheic basins of central Argentina, extending into eastern Chile and southern Bolivia. The northern section of this ecoregion is limited by the drainage divide between the Titicaca basin and the Salinas de la Puna basin, and includes Salar de Atacama and the Puna de Atacama. The northwestern boundary is formed by the Domeyko Range and the eastern boundary is the divide with the Río Salado basin (Pasaje-Juramento-Salado system). The ecoregion also encompasses a series of sierras (Carahuasi, Aconquija, de la Carreta, Humaya, Las Higueritas, and del Potrerillo), and the valley enclosed between sierras Grandes and Comechingones in the west, and Sierra Ancasti in the east. To the south, it extends between the drainage divide with the Río Colorado to the west and the Bonaerensean drainages to the east, reaching the Atlantic coast between the Sierra de la Ventana and the Río Colorado drainage.

Topography

The topography of this ecoregion is varied, with elevations ranging from sea level at Bahía Blanca estuary along the Atlantic Ocean to over 6500 m asl in the Western Cordillera of the Andes in the northern part of the ecoregion (Hijmans et al. 2004). The Western Cordillera forms the boundary between watersheds draining the Pacific and those draining internal basins of the Puna Plateau, which forms the rugged southern extension of the Altiplano (Moreno et al. 2007). To the west of the Puna is the closed basin of the Salar de Atacama in the Salars Depression. This area is separated from the Puna by volcanoes of the Central Volcanic Zone along the Western Cordillera. Further south the ecoregion is bisected by the Sierras de Córdoba, which is a mountain chain that pre-dates the Andes. 

Freshwater habitats

In the north the ecoregion features diverse high-elevation wetlands (saltpans and lagoons), temporary endorheic basins, and some permanent watercourses fed by snowmelt. The middle section includes all of the endorheic watercourses that flow down from the San Luis Hills and the western slopes of the Sierras de Comechingones. Río Quinto is one of the main rivers in this area, draining into the lagoons and wetlands called Bañados de La Amarga in the southern Córdoba Province (López et al. 2002).

To the east is the Río Salí-Dulce. Most of its tributaries descend from the Aconquija and Calchaquí sierras. After passing through Santiago del Estero, it divides into two branches. The southernmost branch, Saladillo, crosses the northern edge of the Salinas Ambargasta where its waters become salty. It then rejoins the main branch, which flows through the Petri marshes before reaching Laguna de Mar Chiquita. With a surface area that fluctuates between 2000 and 6000 km², Mar Chiquita (also known as the Sea of Ansenuza) is one of the largest saline lakes in the world.  This shallow, brackish lake has salinity values ranging from 40 to 250 g/l, and supports abundant birdlife (López et al. 2002).

There are also rivers, creeks and rivulets that descend from the western slopes of the Sierras de Córdoba to the Salinas Grandes salt plains. Most only reach it during the rainy season, and during the remainder of the year fade into marshes or are absorbed by sand expanses called arenales. One of the main water courses is the Río Cruz del Eje (López et al. 2002).

Terrestrial habitats

Terrestrial habitats range from puna and steppe in the north to chaco and espinal in the east and south, respectively. In the Andes plant associations vary according to the altitudinal gradient, and include shrubby steppe, open woods with low trees such as Polylepis tomentella, and shrubs such as Bulnesia retama and Psila spartioides. There are also tall cactuses, halophytic communities, grasses, and cloud forest species such as the tipu tree (Tipuana tipu) and laurel (Phoebe sp.) (López et al. 2002).

The eastern part of the ecoregion is dominated by plant communities of the Gran Chaco. At higher elevations are xerophytic quebracho woods like Aspidosperma quebracho-blanco and Schinopsis spp., and thorny shrubs. Saline soils support communities of algarrobo (Prosopis spp.) and chañar (Geoffroea decorticans), as well as halophytic species. There are also forest and grassland areas, the latter associated with filled-in riverbeds.

The southern part of the ecoregion is characterized by a thorny deciduous shrubland forest called espinal. Species are dominated by the genus Prosopis, particularly the calden tree (Prosopis caldenia) (WWF 2001).

Description of endemic fishes

This ecoregion is home to 21 recorded endemic species, of which nearly half are in the genus Trichomycterus. There are no endemic genera. Other endemics include species of Astyanax, Bryconamericus, Jenynsia, Characidium, Corydoras, and Loricaria.

Justification for delineation

The ecoregion falls into the Western Paranoplatensean and Central Endorheic icthyographic ecoregions defined by López et al. (2002). This area marks the western distributional limit of Paranoplatensean ichthyofauna with species of Characidae and Loricariidae, reflecting a noticeable decline in species compared to the Lower Paraná [345].  It is also marked by the occurrence of endemic species of Trichomycteridae and Anablepidae.

Level of taxonomic exploration

Fair