Araracuara Savanna

On the Araracuara Plateau in the Colombian Amazon a number of savanna-like associations occur. The plateau is of Palaeozoic age and composed of nutrient poor sandstone. The area around the plateau is almost entirely composed of evergreen tropical rain forest and so these savannas are thought to be an edaphic climax rather than a climatic climax. However, the description of the vegetation here is based on a wide concept of savanna because it also includes a mixture of low woodland and scrub. On the top of the plateau patches of low forest with scrub occur characterized by the small tree Dimorphandra cuprea (Fabaceae) and the shrub Ilex divaricata (Aquifoliaceae). The canopy is often closed and ranges in height from 4-6 m. Other typical trees include Dimorphandra vernicosa (Fabaceae), Ocotea esmeraldana (Lauraceae), Ormosia macrophylla (Fabaceae) and Schizaea incurvata (Schizaeaceae), while other frequent shrubs are Gongylolepis martiana (Asteraceae) and Guatteria maquirei (Annonaceae). The herb layer is typified by Pachyloma coriaceum (Melastomataceae), Irlbachia alata (Gentianaceae) and Sauvagesia fruticosa (Ochnaceae). Epiphytes, however, or rare and the few climbers include Doliocarpus dentatus (Dennstaedtiaceae). Lichens (Cladina and Cladonia) are present in small patches and bryophytes form extensive patches on vertical walls and in fissures. Also on the plateau but often associated with gentle slopes is forest and scrub typified by the tree Bonnetia martiana (Theaceae) and the shrub Macairea rufescens (Melastomataceae). It ranges in height from 1.5 to 7 m but never forms a closed canopy. Other characteristic shrubs include Bombax coriaceum (Bombacaceae), Clusia chiribiquetensis (Hypericaceae) and Guatteria maquirei (Annonaceae). The herb layer, on the other hand, is poorly developed especially in the low-forested areas, but commonly includes Abolbodo macrostachya (Xyridaceae), Schoenocephalum martianum (Rapateaceae) and Syngonanthus umbellatus (Eriocaulaceae). Other characteristic species in the herb layer are the terrestrial bromeliad Brocchinia hechtioides (Bromeliaceae), Diplacuum longifolium (Myrtaceae), the orchid Duckeella pauciflora (Orchidaceae), Monotrema aemulans (Rapateaceae), Utricularia longeciliata (Lentibulariaceae) and the lycopod Lycopodiella contexta (Lycopodiaceae). Epiphytes and climbers are again rare but species of the parasitic Struthanthus (Loranthaceae) may be present on Bonnetia trees. Where there is a degree of irregularity in the micro-relief closed swards of tall, mainly graminoids occur. The main species is usually the grass Axonopus schultesii (Poaceae), but Schoenocephalium martianum (Rapateaceae) may be codominant. Scattered small trees and shrubs include Bombax coriaceum, Bonnetia martiana, Macairea rufescens and Mauritia carana, and typical herbaceous species are Catasetum discolor (Orchidaceae) and Curtia tenuifolia (Gentianceae). Other species include the shrub Sauvagesia fruticosa (Ochnaceae) and the herbs Drosera capillaris (Droseraceae), Farringtonia fasciculata and Siphanthera cordifolia (Melastomataceae). Characteristic of shallow sandy soils is an herbaceous formation largely dominated by therophytes but also including a few perennial graminoids. The main species are the grass Paspalum tillettii (Poaceae) and forb Xyris wurdackii (Xyridaceae). Other characteristic species are Genlisca filiformis (Lentibulariaceae), Syngonanthus vaupesanus (Eriocaulaceae) and Xyris araracuavae (Xyridaceae) and a variety of lichens and bryophytes. In rocky areas where thee is only a very thin layer of soil a very low herbaceous formation occurs with occasional dwarf shrubs. The two main species are the herbs Siphanthera hostmannii (Melastomataceae) and Xyris paraensis (Xyridaceae), but about 50% of the species are therophytes and algae cover much of the substratum. On exposed sandstone virtually devoid of soil, an open herbaceous community occurs with scattered dwarf shrubs, lichens and the terrestrial bromeliad Navia garcia-barrigae (Bromeliaceae). Other common species are the dwarf shrubs Acanthella sprucei (Melastomataceae) and Clusia chiribiquetensis (Hypericaceae). The former often has a bonsai-like appearance with prominent roots able to penetrate cracks and fissures for water and nutrients, but most species in this formation appear to be mostly dependent on rainwater for their supply of water.

Guyanan Savanna

Included here are savannas of the Gran Sabana tablelands (at altitudes ranging from 900-1200 m) and the lower tablelands of alluvial fans and upper river terraces. Gran Sabana is a gently rolling plain adjacent to the Guyana Uplands and is actually composed of sediments (mainly so-called white sands) from the Roraima formation, which are not only poor in nutrients but can contain toxic levels of aluminium. The area is also quite dry and can experience two dry seasons per year. In the driest areas treeless grass and sedge savanna has developed in which species of Axonopus, Panicum, Rhynchospora, Scleria and Trachypogon predominate. Common species may include Axonpus pruinosus, A. kaietukensis, Bulbostylis paradoxa, Chalepophyllum guianense, Digomphia laurifolia, Echinolaena inflexa, Euphorbia guianensis, Humiria balsamifera, Hypogynium virgatum, Mahurea exstiputata, Miconia stephananthera, Poecilandra retusa, Rhynchospora globosa, Ternstroemia pungens, Tococa nitens and Trachypogon plumosus. Endemic species associated with Gran Sabana include Brocchinia steyermarkii (Bromeliaceae), Carptotepala insolita (Eriocaulaceae), Clusia pusilla (Hypericaceae), Drosera felix (Droseraceae), Panicum erectifolium (Poaceae), Phoradendron semivenosum (Loranthaceae), Poecilandra pumila (Ochnaceae), Polygala blakeana (Polygalaceae), Roupala minima (Proteaceae) and Trimezia fosteriana (Iridaceae). In the lower tablelands open tree savannas occur. The main woody components are Antonia ovata, Bowdichia virgilioides, Brysonima coccolobaefolia, Curatella americana, Genipa americana, Plumeria inodora, Roupala complicata and Salvertia convallariodora, while the dominant ground layer species are Aristida setifolia, Axonopus canescens, Bulbostylis paradoxa, Echinolaena inflexa, Leptocoryphium lanatum, Thrasya paspaloides and Trachypogon plumosa.

Coastal Savanna

A belt of coastal savanna stretches from Guyana through Surinam and French Guiana and across the Amapa Territory of Brazil to the mouth of the Amazon. It occupies an area of alluvial deposits, mainly coarse sand, situated between the coastal swamps and mangroves and the hinterland rain forest. Within this zone various different types of savanna have been described but it can be broadly divided into grass savanna, tree-shrub savanna and sedge savanna. Occurring in some of the driest areas grass savanna is largely dominated by grasses such as Axonopus purpusii, Leptocoryphium lanatum and Trachypogon plumosus, but may include occasional bushes such as Matayba opaca (Sapindaceae) and Ternstroemia punctata (Theaceae). Tree-shrub savanna includes scattered trees of Byrsonima crassifolia (Malpighiaceae) and Curatella americana (Dilleniaceae), various shrubs and a grass layer that has a similar species composition to grass savanna. Sedge savanna is characteristic of some of the wetter areas and typical includes Lagenocarpus tremulus, Rhyncospora tenuis and Scleria species. In places scattered patches of the palm Mauritia flexuosa (Arecaceae) may also be present.


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