Location and General Description
The Apure/Villavicencio dry forests extend southwest, bordering the eastern Cordillera de Mérida, from Venezuela to the Serranía de Macarena in Colombia. The ecoregion is located in the states of Portuguesa, Barinas, and Apure in Venezuela and the departments of Arauca, Casanare, and Meta in Colombia. The ecoregion is wide in the north and narrows as it extends southward.
The dry forests lie between elevations of 130 and 400 m, with the lower areas located on the eastern side of the ecoregion. The average annual precipitation is 135 mm. The maximum temperature is 33 oC and the minimum 19 oC (Rangel et al. 1987b). This area represents a transition zone between the Llanos and the montane forests in both Colombia and Venezuela
Alluvial fans are present in the Colombian departments of Casanare and Arauca, on the Venezuelan border. These alluvial fans extend to the Llanos ecoregion. The heavily drained soils of the alluvial fans are acid and low in fertility (Rangel et al. 1987b). Some of the information obtained for the ecoregion is specific to these alluvial fans.
This ecoregion has a mosaic pattern of formations changed by humans. Some of these formations contain native semi-deciduous woodland, deciduous thorn forest, and tall grassland. The deciduous thorn forests are principally found in the Venezuelan side of the ecoregion. Some of the flora species are Caesalpinia conaria, Capparis coccolobifolia, C. brasiletto, Cercidium praecox, Chloroleucon mangense, Coccoloba ramosissima, Jacquinia sp., Mimosa sp., Piptadenia flava, Poponax flexuosa, P. tortuosa, and Prosopis juliflora (UNESCO 1981). Semi-deciduous woodland includes Attalea maracaibensis, Bombacopsis quinata, Ceiba pentandra, Cordia sp., Crysophyllum sericeum, Guazuma tormentosa, Gustavia poeppigiana, Inga sp., Macrolobium sp., Mauritia flexuosa, Pouteria anibaefolia, Roystonea venezuelana, Spondias mombin, Tabebuia rosa, and Trichilia maynasiana. The tall grasslands include dense herbaceous growth in some areas. These grasslands include Acrocomia sclerocarpa, Andropogon selloanus, Axonopus canescens, Byrsonima crassifolia, B. coccolobifolia, Curatella americana, and Trachypogon plumosus (Huber and Clara Alarcon 1988).
Steyermark (1982) refers to the area between the Uribante and Arauca Rivers in Venezuela, as a Pleistocene forest refuge with lowland tropical floras. This refuge lies on forested lowland between 100 and 200 masl. The relationship of this forest’s species with the western Amazonian species are exemplified by Capparis sola (Caparidaceae); Licania latifolia (Chrysobalanaceae); Dichapetalum latiflium (Dichapetalaceae); Henrietella rimosa and Leandra aristigera (Melastomataceae); Maxillaria equitans (Orchidaceae); and Piper hermannii (Piperaceae). Other plant species known only to be found in this refuge are Inga thibaudiana, Machaerium paraense, Ormosia nobilis, and Pterocarpus santalinoides (Leguminosae); Miconia matthaei (Melastomataceae); Simaba paraensis (Simarubaceae); and Aegiphila scandens (Verbenaceae) (Styermark 1982).
The flora in the alluvial fans in Colombia includes 232 species, 173 genera and 72 families. The most diverse family is the Rubiaceae with 59 species, followed by the Poaceae with 37 species. The fauna in the alluvial fans that correspond to this ecoregion include 65 species of reptiles, and 144 species of birds (Rangel et al. 1987b). There is no available information for the rest of the ecoregion.
Endemic terrestrial mammals characteristic of this ecoregion, and of others in dry forests in Colombia and Venezuela, are the opossum (Marmosa xerophila), and the vesper mouse (Calomys hummelincki). Marmosa is very well adapted to dry habitats mainly found in deciduous forest, while the vesper mouse is mainly found in sandy grasslands (Eisenberg 1989).
Most of the area has been highly degraded by agriculture and livestock grazing. In Venezuela, the agricultural lands are in the north of the ecoregion. In Colombia, the agricultural lands extend throughout the ecoregion, except for some natural habitat remaining in the lowlands of the Serranía de la Macarena and Tinigua National Parks. These two Parks are the only protected areas located in the southernmost part of the ecoregion.
The Apure/Villavicencio dry forests are poorly represented in the protected areas. Sierra Nevada National Park. (IUCN Category II) contains paramo, moist forest and some dry forest. This 276,446-ha Park is located in the north of the ecoregion. Serranía de la Macarena National Park (IUCN category II), located in the south of the region, consists of 630,000 ha. The Park has different ecosystems including, savannas, dry forests, tropical lowland forest, and montane forests. This Park has deteriorated areas that were caused by migrants, and by the Park officials' mismanagement (Rangel et al. 1987a). The Tinigua National Park (IUCN category II), has an area of 201,785 ha. The Park is located in a valley between the Sierra Macarena and the East Andes. The majority of the park consists of tropical lowland forest.
Types and Severity of Threats
Some areas have been severely altered by logging and for use as agricultural fields and for livestock grazing. Logging and hunting in the southern part of the ecoregion, especially in the Sierra de la Macarena and Tinigua National Parks have also lead to changes in the natural state of the ecoregion (Rangel et al. 1987a). The illegal commerce of coca has caused further environmental degradation on the Colombian side. Water pollution in the Arauca River (on the border of Colombia and Venezuela) due to high concentrations of sodium left after the oil is refined. The water is later discharged in small watersheds and wells, which in turn lowers the quality of the ground water and the soils (Rangel et al. 1987b).
Justification of Ecoregion Delineation
The delineation’s for this ecoregion were derived from various national vegetation cover maps. These dry forests represent a transitional area between the llanos savannas and the montane forests of the eastern Andes, and are host to a number of endemic species. Portion in Venezuela follow Huber and Alarcon (1988). Linework follows their classification of "western llanos" (subregion B.21), within which are grouped "semi-deciduous piedmont forests", "semi-deciduous riparian forests", "matorral", "piedmont savanna", and "forest-savanna". The extension of this ecoregion into Colombia follows Navarro et al. (1984).
Eisenberg, J.F. 1989. Mammals of the Neotropics: The Northern Neotropics Volume 1. The University of Chicago Press, Chicago.
Huber, O. and Clara Alarcon. 1988. Mapa de vegetacion de Venezuela. Republica de Venezuela, Ministerio del Ambiente y de los Recursos Naturales Renovables, Caracas, Venezuela.
Navarro, A.E.S., G.H. Peña, F.C. Lemus, J.R. Baquero, R.F. Soto. 1984. Bosques de Colombia. IGAC-INDERENA-CONIF, Bogota, Colombia.
Rangel, J.O., M. Aguilar, and P. Lowy. 1987a. Parque Nacional Natural Sierra de la Macarena. Colombia Diversidad Biotica I. INDERENA-Universidad Nacional de Colombia, Bogota, Colombia.
Rangel, J.O., H.L.P. Sanchez, M. Aguilar, and A. Castillo. 1987b. Region de la Orinoquia.J.O. Rangel, editor. Colombia Diversidad BioticaI. INDERENA-Universidad Nacional de Colombia, Bogotá, Colombia.
Steyermark, J.A. 1982. Relationships of some Venezuelan forest refuges with lowland tropical floras. G. Prance, editor, Biological diversification in the Tropics. Colombia University Press, New York.
UNESCO. 1981. Vegetation map of South America: Explanatory notes. UNESCO, Paris.
Prepared by: Claudia Locklin
Reviewed by: In process