Location and General Description
The Southern Andean Yungas are loosely bordered to the east by the Chaco, and tightly interdigitated to the west with Bolivian Montane Dry Forest, spanning southwestern Bolivia and northwestern Argentina (Olson et al. 2000). The northern, southern, western and eastern boundaries of this ecoregion terminate at approximately the 170 and 280 south latitudes and 670 and 630 west longitudes, respectively (Anon. 1980). The wet and humid climate is deposited by northern trade winds, and rains typically exceed 2500 mm/yr (Stattersfield et al. 1998). The altitude generally ranges 800 – 2500 m, but may reach heights exceeding 3000 m (Stattersfield et al. 1998).
This ecoregion essentially forms a mesic habitat that lies between two much drier habitats: the Chaco to the east, and the higher Puna to the west (Olson et al. 2000). The habitat is evergreen forest, with canopy height typically not exceeding 15 m (Stattersfield et al. 1998). Between 1200 – 2500 m the forest is dominated by Andean Alder (Alnus acuminata) and Mountain Pine (Podocarpus parlatorei) or Queñoa (P. australis); at lower elevations these species form a mosaic with other trees, especially Lauraceae and Myrtaceae (Ojeda and Mares 1989, Stattersfield et al. 1998).
Like the Bolivian Yungas to the north, this region is also quite strong in endemics, including approximately 10 avian species that are range-restricted, including species such as the Red-faced Guan (Penelope dabbenei), Rothschild’s Swift (Cypseloides rothschildi) and the Rufous- throated Dipper (Cinclus schulzi) (Stattersfield et al. 1998).
Many strongly tropical species meet their southern limits of geographic distribution in this region (Ojeda and Mares 1989). In light of the strong affinities of this region to typical lowland evergreen forest (Nores 1992), the high diversity of wide-ranging, lowland Neotropical mammals of large size is quite likely. Examples include a variety of herbivores such as White-lipped and Collared Peccary (Tayassu) and Lowland Tapir (Tapirus terrestris), as well as cats such as Jaguar (Panthera onca), Puma (Puma concolor), Margay (Felis wiedii) and Jaguarundi (Herpailurus yagouaroundi) (Chalukian n.d., Brooks 1991, Tarifa 1996).
The extent of deforestation in Bolivia has not been documented with certainty, but there are large areas of degraded land (Fjeldså and Mayer 1996). However, some large and intact regions still persist in Bolivia, such as the forests between the Pilcomayo and Pilaya rivers in Montes Chapeados that span ~1300 km2 (Stattersfield et al. 1998). The situation in Argentina is apparently grave as more than one-half of the original forest has disappeared (Vervoost 1979), due to logging, agriculture, exotic Pinus invasion, road development, human colonization and unsustainable tourism (WWF/IUCN 1997).
There are a number of National Parks (NPs) and protected areas in this ecoregion, in both Bolivia (Tariquía National Reserve – 2469 km2) and Argentina (Calilegua NP - 760 km2, Baritú NP - 724 km2, El Rey NP - 442 km2, Potrero de Yala Provincial Park - 43 km2) (Chalukian n.d., Stattersfield et al. 1998).
Types and Severity of Threats
Unfortunately, most of these parks are of smaller size in light of how threatened the region is overall. This is especially the case in Argentina, where the total km2 of the combined four Argentinean parks (1969 km2) does not even rival the single Bolivian park in this ecoregion. However, a proposal under consideration by the government of Tucumán, Argentina would create the Campo de los Alisos NP (2500 km2) (Halloy et al. 1994), thereby more than doubling the km2 of protected area in this threatened ecoregion.
Justification of Ecoregion Delineation
The delineation for these southern yungas were to represent the distinct montane transitional forests of the southern Andes from high puna habitats to the lowland forests below. These rugged mountains and foothills host many endemic species and astounding beta-diversity on both an elevational and latitudinal gradient. The linework for the Bolivian portion follows the Ribera et al (1994) classification of "subandean montane forest" and "subandean submontane forest", both of the Tucuman-Bolivian geologic formation. The Argentine portion follows a number of sources, including Morello (1968) and Cabrera (1976), but final linework follows the natural regions map of Daniele and Natenzon (1994) who classify this as "forest of the yungas".
Anon. 1980. Time-Hammond World Atlas. Hammond, Inc., U.S.
Brooks, D.M. 1991. Preliminary comparisons of large mammal guilds in five semi-arid environments of the New World. Proc. IX Mtg. Tx. Soc. Mamm., Junction, Texas.
Cabrera, A. L. 1976. Regiones fitogeográficas Argentinas. Enciclopedia Argentina de Agricultura y Jardinería, Second Edition, Vol. II, Buenos Aires, Argentina.
Chalukian, S. n.d. Evaluación preliminar de la distribución, status y habitat del tapir (Tapirus terrestris) en la region de las Yungas, noroeste de Argentina.
Daniele, C., and C. Natenzon. 1994. Regiones Naturales de la Argentina. Draft map. Argentina National Parks Department, Buenos Aires, Argentina.
Halloy, S., J.A. González and A. Grau. 1994. Proyecto de creación del Parque Nacional Aconquija (Tucumán, Argentina): Rpt. No. 4. Fund. Miguel Lillo, Nat. Cons. Ser. 9, Tucumán.
Fjeldså, J. and S. Mayer. 1996. Recent ornithological surveys in the Valles region, southern Bolivia and the possible role of Valles for the evolution of the Andean avifauna. Cntr. Rsrch. Cult. Biol. Divers. Andean Rainforests, Danish Envion. Rsrch. Prog.
Morello, J. 1968. La vegetación de la República Argentina, No. 10: Las grandes unidades de vegetación y ambiente del Chaco Argentino. Buenos Aires, Argentina.
Nores, M. 1992. Bird speciation in subtropical South America in relation to forest expansion and retraction. Auk 109: 346-357.
Ojeda, R.A. and M.A. Mares, 1989. A Biogeographic Analysis of the Mammals of Salta Province, Argentina: Patterns of Species Assemblages in the Neotropics. Spec. Publ., Mus. Texas Tech Univ. 27.
Olson, D., E. Dinerstein, P. Hedao, S. Walters, P. Allnutt, C. Loucks, Y. Kura, K. Kassem, A. Webster and M. Bookbinder. 2000. Terrestrial Ecoregions of the Neotropical Realm (map). Conserv. Sci. Program, WWF-US, DC.
Ribera, M.O., M. Libermann, S. Beck, and M. Moraes. 1994. Mapa de la vegetacion y areas protegidea de Bolivia. 1:1,500,000. Centro de Investigaciones y Manejo de Recursos Naturales (CIMAR) and Universidad Autónoma Gabriel Rene Moreno (UAGRM), La Paz, Bolivia.
Stattersfield, A.J., M.J. Crosby, A.J. Long and D.C. Wege. 1998. Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. Birdl. Cons. Ser. 7, Cmabridge, UK.
Tarifa, T., 1996. Mamíferos. Pp. 165-264. En: P. Ergueta y C. de Morales, editors, Libro Rojo de los Vertebrados de Bolivia CDC-Bolivia.
Vervoorst, F. 1979. La vegetación del noroeste argentino y su degradación. Ser. Cons. Natu. Fund. Miguel Lillo 1: 5-9.
WWF/IUCN. 1997. Centres of plant diversity: A guide and strategy for their conservation, 3: North America, Middle America, South America, Caribbean Islands. WWF and IUCN, Cambridge, UK.
Prepared by: Dr. Dan Brooks
Reviewed by: In process