Location and General Description
This region is located on the northeast coast of South America. The Amazon basin lies to the south and the Orinoco borders on the west. The primary rivers from west to east, draining north towards the Atlantic Ocean, are the Essequibo, Corantijn, Marowijne, and Oyapock. The southern boundary is formed by the watershed of the Acarai Mountains and Serra Tumucumaque, which also is the international border between Brazil and the northern Guianan countries of Guyana, Suriname, and French Guiana (an overseas department of France). A small portion to the east includes the upper tributaries of the lower Amazon in Brazil. Parts of the lower Orinoco in Venezuela comprise the western limit. The Guianan Moist Forests exclude the narrow strip of coastal mangroves and swamp forest skirting the Atlantic Ocean.
The local and regional climate types in these forests are generally hot and wet, and are strongly influenced by the northeastern trade winds (vientos alisios) and the Intertropical Convergence Zone (ITCZ). The result is that moisture-rich air is constantly blown inland from the Atlantic – regulated by annual oscillations of the ITCZ. There is some variation in precipitation through the region, which can range between 2000 – 4000mm annually. Climate in this region is hot and wet. According to Köppen's climate classification, the major part of this ecoregion has a Tropical Rainforest (Af). Two rainy and two dry seasons can be distinguished: a short rainy season from early December to the end January, a short dry season from early February to the end April, a long rainy season early May to mid August, and finally a long dry season mid August - end November (Teunissen et al. 2001).
The ancient Precambrian Guianan Shield is the underlying geology in northeastern South America (Gibbs and Barron 1993). The Guianan Moist Forests accounts for approximately two-thirds of the northeastern portion of the Shield, but the west-central area includes the elevated sandstone plateau of the Pakaraima Highlands with an average elevation of 1,000 m (Huber 1995). There are also associated table-top mountains (tepuis) such as Mount Roraima that raise above the surrounding area to heights of 2,810 m. These two higher elevation areas are described in the Tepuis ecoregion. The region has primarily a level or low to hilly physiography, with some abrupt topography along the river valleys and in proximity to tepui formations.
Vegetation is tropical ombrophilous lowland forest, with moderate regional variability, including marsh forest along rivers. Several vegetation types are recognized within this ecoregion and also include patches of savannas and some patches of herbaceous swamps along the coastal lowlands (Lindeman and Mori 1989). Several outliers of the Tepui formations are embedded in and rise from these predominanty lowland and submontane forests. The flora of this area is rich, and these multi-tiered forests can reach up to 40 meters in height. Although primarily evergreen, there may be marked leaf reduction in the dry season(August-December). In much of the area the forest floor is rich in shrubs (not many shrubs) and herbaceous plants, and epiphytes and parasites abound due to high atmospheric humidity (UNESCO 1981).
The chief plant families represented in these forests are Bignonianceae, Bombacaceae, Euphorbiaceae, Moraceae, Sterculiaceae, Lauraceae, Vochysiaceae, Sapotaceae, Lecythidaceae, leguminous plants, Combretaceae, Anacardiaceae, Rubiaceae, Meliaceae, Sapindaceae, Annonaceae, and Palmaea. Common tree species include Calophyllum brasiliense, Carapa guianensis, Cedrela fissilis, Ceiba pentandra, Coumourana punctata, Couroupita guianensis, Eschweilera sp., Guarea trichiloides, Luehea sp., Coumourana punctata, Parkia pendula, Pentaclethra macroloba, Protium sp., Schwartzia sp., Trichilia sp., and Warszewiczia coccinea. Within the Guianas, moist forest species composition is changing from east to west. Even within the boundaries of Suriname, species composition between east and west is very obvious: many "eastern" species are completely lacking in western Suriname, while typical "western" species (lacking in eastern moist forest) may dominate "western" forests. Lacking completely in Suriname are: Cedrela fissilis, Coumourana punctata, Coumourana punctata and Warszewiczia coccinea.
This ecoregion encompasses a large block of lowland and submontane forest, with a wide variety of regional and local floral and faunal biodiversity, and with high levels of species endemism and richness. Since the first explorers and biologists arrived here this areas has been recognized as an important center and dispersal route for many species (Schomburgk 1940)
Little research had been done on much of this region until recently, and historic accounts were not maintained in the host country where much valuable information has been lost (Fontaine pers.comm).
Mammalian richness is high, with over 220 species described in Guyana alone – of which over 100 are bats. Endemism is also relatively high on the species level, and includes the following species: Marmosa lepida, Euphractus sexinctus, Sanguinus midas, Pithecia pithecia, Ateles paniscus, Sciurillus pusillus, Oryzomys delicatus, Neacomys guianae, Sphiggurus insidiosus, Echimys chryurus (Eisenberg 1989), Tonati schulzi, and Molossops neglectus (Mittermeier et al.. 1990).
Avian richness and diversity are high, and shares affinites with the Guyana Highlands and northern Andes (cock of the rock Rupicola rupicola) as well as the Amazonian lowlands (hoatzin Opisthocomus hoazin). Many microhabitat specialists also florish in the diverse terrain, and may greatly increase the overall richness of the area. Several larger raptors, including harpy (Harpia harpyja) and crested eagle (Morphnus guianensis) occur locally.
Very little is know of the herpetofauna present in these forests. Threatened reptiles include the black caiman (Melanosuchus niger) and the yellow-headed sideneck turtle (Podocnemis unifilis). Among the amphibians, diversity is notably high among the Hylindae, Dendrobatidae, and Peptodactylidae (Mittermeier et al. 1990).
Plant endemism and richness is high, and of the estimated 8000 species of vascular plants – 50% may be endemic (Mittermeier et al. 1990, Boggan et al. 1997). The vegetation is typical of what has come to be know as the Guyana Lowland Floristic Province. The southern portion of this ecoregion is a Center of Plant Diversity (WWF & IUCN 1997) known as the transverse dry belt, and in central French Guiana is another Center known as the Saul Region. Within the transverse dry belt the predominant vegetation is semi-open forest with notable patches of savanna. Dense mesophylic forests are common on higher elevations and along rivers and streams. In this area palm diversity is notably high and includes such species as Astrocaryum mumbaca, A. munbaca, Bactris sphaerocarpa (not in Suriname), Maximiliana maripa, and Iriartea excrrhiza. The Saul region is more characteristic of the Guayana Lowland Floristic Province, and within its small confines has over 150 endemic vascular plants (IUCN 1996).
In a patchwork distribution among these moist forests are an important savanna component, predominantly in Suriname. Savannas can be considered as remnants of the extensive Pleistocene climate savanna, once covering Suriname almost entirely except along rivers and at high altitudes where the rainforest survived in so-called forest refugia. While the savanna climate during the early Holocene changed into the present tropical rainforest climate, Suriname became covered again by rain forest and savanna ecosystems survived in 10 different landscapes at locations where soil/hydrology and/or man-made fires favored their maintenance. Nowadays savanna's are covering only 1 % of the Surinamese land surface. Based on the landscape classification of Cohen and Van der Eyk (1953) all savanna types were studied in the 60s and early 70s.
The total list of savanna plants amount over 800 species, which is 20 % of the Surinamese flora. Most of these species are confined to savannas. As savannas cover only 1 % of the land surface of Suriname, savannas may be considered as hot spots for plant diversity.
At present, the siege of human invasion has only just begun in this ecoregion – and conservation efforts as well have taken rootThis ecoregion occurs in five countries, which speak five different languages. Governments agendas are equally diverse, and management and conservation occurs nationally with few transnational efforts currently in place. French Guiana, Guyana, and Suriname are unique among South American countries in that deforestation pressures have so far had little effect (IUCN 1996). On the other hand there are also very few protected areas, (with the exception of Suriname) and threats have increased dramatically even as we enter the next millenia.
There are a number of established and proposed nature reserves in Guyana, Suriname, and French Guiana which offer varying degrees of protection – however few are officially recognized (Lindeman and Mori 1989). UNEP recognized the following protected areas within and shared by this ecoregion: in Guyana, Kaieteur National Park (5¸00'N - 59¸00'W, IUCN category II), and in Suriname, Brownsberg Nature Park (4¸54'N - 55¸12'W, IUCN category II) 12 nature reserves, and one multiple use management area (UNEP/WCMC protected areas database.
There are is a significant push to increase tourism in these countries, which may help in the valuation of biodiversity and curve some of the current trends. Governments are also becoming more aware of the true "richness" their countries possess and are taking measures to save it.
Types and Severity of Threats
Gold mining and the rampant expansion of logging are the most serious cause for concern, much of which is done illegally and along the borders of the Guyanas and Brazil and Venezuela where there is little enforcement or protection. Recent increases in gold mining have severely impacted streams and surrounding landscapes with polluted runoff and mercury contamination (Fontaine per. comm.). Guyana is the second largest exported of wild birds in South America, with approximately 15,000 exported in 1989 (IUCN 1996). Other wildlife is also exported commercially and together may constitute a threat to the persistence of many species. However, stringent quotas currently exist and with proper research and enforcement may limit the effects of this threat.
Justification of Ecoregion Delineation
The delineation for this ecoregion follow five separate national and international vegetation maps. The base map was UNESCO (1980), and all subsequent maps were used to refine these lines on a national level. In Venezuela we used Huber and Alarcon (1988), following their classification of "semi deciduous tropophilous medium forests", "semi deciduous tropophilous tall forests", "evergreen submontane ombrophilous forests", and "evergreen tall ombrophilous forests (south of the Delta)". In Guyana, linework follows Huber et al. (1995), and encompasses all their Flooded Coastal and Lowland Forests and Shrublands forest types, and excludes all Savannas and Meadows. In Suriname we followed OAS & National Planning Office of Suriname (1988) and excluded all swamp forests and mangroves in the northern sector, and a small portion of savanna along the southern border with Brazil. All of French Guiana was included with the exception of mangroves according to UNESCO (1980) and Granville (1979). In Brazil, we followed IBGE’s (1993) classification of "dense submontane ombrophilous forests" along the borders of the Guyanas and the southern delineation follows elevational contours.
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Prepared by: Jan Schipper, Pieter Teunissen, and Burton Lim
Reviewed by: In process