This transitional habitat is located between the
montane forests of the eastern Andean slope
and the lowland grasslands. The ecoregion is a
mosaic of premontane forest, dry forest,
savanna, and gallery forest. Small mammals are
characteristic of area and include a mouse
opossum (Marmosa xerophila), a vesper mouse (Calomys hummelincki) and the giant
anteater (Myrmecophaga tridactyla). Only two parks, the Serranía de la Macarena and
Tinigua National Parks, are located within this
ecoregion that as been almost destroyed by agriculture and livestock grazing.
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
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
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