Included here is the lowland region known as llanos extending through northern Colombia and western Venezuela. It also extends along the coastal zone of Venezuela from the Paraguana Peninsula west to the start of the Amacuro Delta and incorporates the middle reaches of the Orinoco River. The remaing seasonal forests are thought to be remnants of much more extensive forest in the past.

Semi-Deciduous Gallery Forest

Many of these linear stretches of forest are thought to be relicts of a once more extensive forest but some have now been modified by human intervention. The forests associated with Delgadito Creek in Venezuela’s Portuguese State, however, are thought to be largely undisturbed. They extend for some 4000 ha and characteristically have three tree stories. Most of the tree species are evergreen and the upper canopy can reach heights of up to about 22 m. The dominant trees of the upper canopy include Astronium graveolens and Samanea saman together with Albizzia caribensis, Hura crepitans, Lecythis ollearia and Trichilia unifoliata. The middle stratum ranges from 10-20 m and typically includes Calycophyllum candidissimum, Cecropia peltata, Guazuma ulmifolia and Guettardia divaricata. Between 8-10 m, palms such as Attalea butyracea and Bactris major largely dominate the lower stratum. Of particular interest for its timber value is Astronium graveolens and so its presence is usually a good indicator that forest has not been disturbed. Among the endemic species associated with these forests is Gustavia acuta (Lecythidaceae).

Relict Forest on Savanna

On the Colombian Llanos savanna has been found in scattered locations such as dunes, dissected high plains and at the foot of mountains. Three types have been identified but one of them the Melinis minutiflora Savanna is regarded as a highly modified as a result of human intervention.  The other two are described as Trachypogon ligularis-Paspalum carinatum Savanna and Paspalum carinatum Savanna. The former, dominated by the two-bunchgrass species Trachypogon ligularis and Paspalum carinatum occur on dunes on the aeolian plain. Other commonly associated grasses included Axonopus purpusii, Gymnopogon foliosus, Leptocoryphium lanatum and Paspalum pectinatum while other frequent components are the sedges Bulbostylis junciformis and Rhynchospora barbata and the endemic forb Schieckia orinomensis (Haemodoraceae). The presence of shrubs, such as species of Miconia, show that these formations would probably develop into woodland if left undisturbed, which is further supported by the presence of relict forest in some of the more inaccessible places. These typically form stands up to 10 m high with occasional emergents and support an under storey of sedges and bromeliads. Open stands of the tree Bowdichia virgilioides are also present in places. Paspalum carinatum Savanna is mainly confined to sloping terrain in the dissected high plain. The bunchgrass Paspalum carinatum dominates but species diversity is general low. On the other hand, several characteristic species occur such as the grasses Aristida implexa, Mesosetum loliiforme and Trachypogon montufari and the sedge Bulbostylis paradoxa. In the less disturbed areas such as south of the Guaviare River, relict evergreen forests are present, but these are mainly confined to isolated ravines and south facing slopes.

References

Berroterán, J. L. 1998. Spatial representation, biodiversity, and fragmentation of vegetation communities of the central high llanos of Venuzuela. In: Forest Biodiversity Research, Monitoring and Modeling. Eds. F. Dallmeier and J. A. Comiskey. Man and the Biosphere Series, Volume 40. The Parthenon Publishing Group.

Berroterán, J. L., Ramos, S., Oropeza, E., Rosales, A. & Piccoli, V. 1998. Relationships between floristic composition, physiognomy, biodiversity and soils of the ecological systems of the central high Llanos of Venezuela. In: Forest biodiversity in North, Central and South America and the Caribbean. Eds. F. Dallmeier and J. A. Comiskey. Man and the Biosphere Series, Vol. 21. The Parthenon Publishing Group.

Daly, D. C. & Mitchell, J. D. 2000. Lowland vegetation of tropical South America – an overview. In: Imperfect Balance: Landscape Transformations in the pre-Columbian Americas. Ed. D. Lentz. Columbia University Press, New York.

Hammen, T. van der. 1979. History of the flora, vegetation and climate in the Colombian Cordillera Oriental during the last five million years. In: Tropical Botany. Eds. K. Larsen and L. B. Holm-Nielsen. Academic Press.

Huber, O., Duno, de Stefano, R., Aymard, G. & Riina, R. 2006. Flora and Vegetation of the Venezuelan Llanos: A Review. In: Neotropical Savannas and Seasonally Dry Forests. Plant Diversity, Biogeography, and Conservation. Eds. R. T. Pennington, G. P. Lewis and J. A. Ratter. Taylor & Francis.

Myers, J. G. 1933. Notes on the vegetation of the Venezuelan Llanos. Journal of Ecology, 21: 335-349.

Prance, G. T. 1982. Forest Refuges: Evidence from Woody Angiosperms. In: Biological Diversity in the Tropic. Ed. G. T. Prance. Columbia University Press.

Stergios, B., Comiskey, J. A., Dallmeier, F. Licata, A. & Nino, M. 1998. Species diversity, spatial distribution and structural aspects of semi-deciduous lowland gallery forests in the western Llanos of Venezuela. In: Forest biodiversity in North, Central and South America and the Caribbean. Eds. F. Dallmeier and J. A. Comiskey. Man and the Biosphere Series, Vol. 21. The Parthenon Publishing Group.

Steyermark, J. A. 1979. Plant refuge and dispersal centres in Venezuela: their relict and endemic elements. In: Tropical Botany. Eds. K. Larsen and L. B. Holm-Nielsen. Academic Press.