Llanos region

FIGURE 5.1 Location of the Llanos region in Venezuela (map by R. Schargel). 

As a result of this mainly Tertiary and Quaternary geological and tectonic history, four principal geomorphological landscapes determining soils, vegetation and fauna can be identified in the Llanos region (Figure 5.2). 

FIGURE 5.4 Isohyets of the Venezuelan Llanos region, based on data from the Ministry of the Environment (Ministerio del Ambiente y de los Recursos Naturales). 

The Llanos region covers approximately one-quarter of Venezuela and contains approximately one-fifth of its total vascular plant flora of 15,353 species, according to Huber et al. (1998). Curiously, the Llanos flora represents also ronghly one-fifth of the total angiosperm flora of the country but only one-tenth of its fern flora this difference is probably a result of the unfavourable climatic conditions in the Llanos for the growth of a more diversified fern flora and of the large extension of floodplains. 

The natural vegetation of a large majority of the Venezuelan Llanos region consists of a complex mosaic of herbaceous ecosystems, especially savannas. The next most important biome of these wide plains is that of the forests, ranging from small areas of evergreen (ombrophilous) lowland forests to entirely deciduous (tropophilous) low forests, and to riverine forests of the gallery type. 

Three natural monuments are usually cited for the Llanos region, but they are all located outside the Llanos proper and consist essentially of atypical Llanos landscape features, such as calcareous mountains or other montane environments in the transition zones between the Coastal Cordillera and the northern Llanos piedmont. 

Regional metamorphism, the wide-scale alteration of rocks during major tectonic events, can produce spectacular textures and structures in rocks, including folds of layers of rocks, folds of individual minerals (mica, for example), and rotated garnet crystals. Examples of regional metamorphism abound, from Acadia National Park in Maine and the Appalachian Mountains in the eastern part of the United States, to the Llano Uplift of central Texas, and the Precambrian rocks of the Grand Canyon. The Alps of Europe and the Himalayas of Asia also show effects of regional metamorphism. 

This chapter aims to provide an update on recent advances in floristic knowledge of one of the major neotropical savanna regions. The imminent publication of the Catdlogo anotado e ilustrado de la Flora Vascular de los Llanos de Venezuela gives evidence of another serious effort to cover progressively all major biomes of Venezuela as a matter of fact, its appearance coincides with the conclusion of one of the most important floristic projects of the Neotropics, the monumental Flora of the Venezuelan Guayana by Steyermark et al. (1995-2005, in nine volumes). 

According to Kbppen s classification (1936), the Llanos are dominated by two climate types Am (tropical monsoon climate type) in the south-western region of Apure state and in the eastern Llanos reaching the Orinoco Delta, and Aw (tropical savanna climate type) in all the remaining area. 

Somewhat older (Pleistocenic) alluvial plains are widely scattered over the Llanos, especially along the northern bank of the Orinoco river and in certain regions of the states of Barinas and Apure. Ultisols are, again, one of the more important soil types of these plains, but Alfisols can also be found under forest cover near the Andean piedmont of Barinas. 

In the same region of the High Llanos, characteristic forest islands locally called matas are regularly found in the shrab savannas (Vareschi, 1960 Vareschi and Huber, 1971) these entirely deciduous, up to 25 m tail and mostly circular forest spots are often dominated by huge trees of Copaifera officinalis (Jacq.) L., accompanied by Jacaranda obtusifolia Bonpl. and Connarus venezuelanus BaiU. var. orinocensis Forero. 

---