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Venezuela´s Eco Regions

 

Guayanan Highlands moist forests  

This ecoregion is located in the highlands of southern Venezuela and northern Brazil, and
extends into western Guyana and Eastern Colombia. The region sits on the Guayanan
Shield which underlies the northern region of South America. It hosts vast expanses of tall
primary rainforest and open, treeless or nearly treeless savannas, and rich gallery forests.
Elevations range from 500-1500 m above sea-level, and the climate is seasonal and
humid, with 2000-2400mm rainfall annually. Here, rugged terrain and unique creatures
abound, as this region is an elevational "island" surrounded by llanos and lowland
forest. 

Location and General Description 

Situated in southeastern Venezuela in northern South America, the Guayanan
Highlands ecoregion is distinct from other ecoregions in Amazonia due to its montane
physiography. It hosts vast expanses of tall primary rainforest and open, treeless or
nearly treeless savannas interrupted by gallery forests. The region is perforated by a
series of ancient uplands and highlands between 500 and 3,000 m in elevation, the
tallest ones are comprised in the Tepui ecoregion (described separately). Portions of
the Guayanan Highlands ecoregion lie in the northernmost tip of Brazil, with small
slivers in western Guayana and eastern Colombia. Most of this ecoregion lies within
the eastern portion of the Orinoco Basin which drains into the Caribbean Sea from
Venezuela. Another portion drains into the Amazon Basin. The major rivers entering
the Orinoco Basin from this ecoregion are the Orinoco headwaters, the Ventuari,
Caroní, Paragua, and Caura in Venezuela. In the southern potions, the Rio
Uraricuera and Rio Branco (in Brazil) drain into the Amazon. 

The ecoregion sits upon the Guayana Shield which underlies the northern region of South
America. It consists of a rock basement with a variety of igneous and metamorphic rocks formed
during different geological events. The upland terraces and mountains of the Guayana Shield
are remnants of highly weathered and ancient parent material consisting mostly of quartzitic or
sandstone rocks, although granitic rock types persist in some areas. The lowland plains
emerged only recently from lacustrine and marine environments. The soils are generally sandy
and poor in nutrients. The seasonal climate is humid to subhumid with 2,000 to 2,400 mm of
rainfall distributed evenly though the year. The average annual temperature is approximately 24°
C.

The landscape is a mixture of mostly forested lowlands of undulating peneplains and
floodplains with a patchwork of upland elements. The topographic features of the uplands
include rounded hills and low mountaintops from 500 to1,500 m elevation, undulating high
plains, lower slopes of the Tepuis, and summit areas of the lower Tepuis. The southeastern
uplands of Venezuela are mostly unexplored botanically, but the ecoregion is characterized by
high floristic and ecological diversity. 

The peneplains lie between the Caura and Paragua Rivers that bisect the ecoregion and
comprise gently undulating lowlands interspersed with low hills to 500 m elevation (Huber
1995b). These rolling lowlands host tall evergreen forests (30-40 m) with dense crowns and
some emergent trees in the genera Calophyllum, Anacardium, Manilkara, Protium, Inga,
Parkia, Copaifera, Erythrina, and Dipteryx. On the plains, abundant trees include Micropholis
melinoniana, Dacroydes sp., Euterpe precatoria, and Quassia cedron. In the hilly habitat,
fewer emergents are represented in forests of Newtonia suaveolens, Couratari guanensis,
Alexa sp., Euterpe precatoria, and Micrandra minor.

The annually flooded riverine forests in the ecoregion are similar in both physiognomy and
composition to the flooded forests of Amazonia (Daly and Mitchell 2000). Some of the more
important tree species on the upper Orinoco portion of the ecoregion include Combretum
frangulifolium, Gustavia augusta, Pterocarpus sp., Etaballia dubia, Albizia corymbosa,
Spondias mombin, Mabea nitida, Eschweilera tenuifolia, Astrocaryum aculeatum, and Inga
spp. The tree species that occupy the floodplains have a broad distribution across Amazonia.
They are exemplified by Caryocar microcarpum, Caraipa densifolia ssp. densifolia,
Macrolobium acaciaefolium, Abuta grandfolia, and Panopsis rubescens .

Biodiversity Features

The region hosts 209 mammals. Many are widespread Amazonian species, including
jaguars (Panthera onca), pumas (Puma concolor), tapirs (Tapirus terrestris), two
peccaries (Tayassu pecari and T. tajacu), and deer (Mazama spp.). Other
mammals that have a restricted distribution include several opossums (Didelphis
albiventris, Lutreolina crassicaudata, and Marmosa robinsoni), bats
(Pteronotus davyi, Lonchorhina fernandezi, and Sturnira ludovici), an endemic
olingo (Bassaricyon beddardi), and endemic rodents (Sciurus flammifer,
Proechimys hoplomyoides, and Dasyprocta guamara).

The avifauna is comprised of about 631 species, few of which are endemics. A number of
species have a restricted distribution; however, including white-cheeked pintails (Anas
bahamensis), aplomado falcons (Falco femoralis), brown-throated parakeets (Aratinga
pertinax), pavonine cookoos (Dromococcyx pavoninus), vermiculated screech owls (Otus
guatemalae), burrowing owls (Athene cunicularia), five species of emeralds and hummingbirds
in the Amazilia genera, chestnut-tipped toucans (Aulacorhynchus derbianus), smoke-colored
peewees (Contopus fumigatus), orange-crowned orioles (Icterus auricapillus), gray seedeaters
(Sporophila intermedia), two-banded warblers (Basileuterus bivittatus), and black-backed
water-tyrants (Fluvicola albiventer).

Reptiles and amphibians are abundant. The more famous snakes that occur here including the
fer-de-lance (Bothrops asper), palm pit-vipers (Bothriechis spp.), coral snakes (Micrurus spp.),
boa constrictors (Boa constrictor), and bushmasters (Lachesis muta). Iguanas (Iguana iguana)
are ubiquitous and tegus lizards (Tupinambis) common.

Current Status 

Many of the interior forests of the Guayana highlands ecoregion are intact. Habitat
destruction from large-scale agriculture, mining, and cattle raising occurs mostly along
the northern and northeastern periphery of the ecoregion, nearest urban centers
(Huber 1995a). Prohibition of commercial logging in the Venezuelan state of
Amazonas curtails activities, but other areas are subjected to logging activities. The
largest UNESCO biosphere reserve in the tropics, the Alto Orinoco-Casiquiare
Biosphere Reserve, lies partly in this ecoregion. The Canaima National Park protects
30,000 km2 of dense evergreen submontane and montane forests, shrublands,
savannas, and broad-leaved meadows, and some high tepui vegetation. A number of
other national parks have been established, but most are insufficiently staffed and
with few or weak management plans. The national parks Parima-Tapirapecó in the
southernmost tip of Venezuela, Serranía La Neblina in Venezuela, and Pico da
Neblina in Brazil together cover about 40,000 km2 of evergreen lowland,
submontane, and montane forests and a number of tepui peaks. Many small national
monuments and forest reserves exist in this ecoregion, but mostly protect the highest
zones of the tepuis.

Types and Severity of Threats 

Until recently, the habitat of the Guayana Highlands ecoregion has been protected
from encroaching commercial exploitation by inaccessibility (Huber 1995a). Most
development and colonization is occurring in the north of the ecoregion, but timber
activities are penetrating the remote interior following road-building activities. The
spread of mining and large-scale agricultural developments in the interior of the
ecoregion is also steady. Both legal and illegal mining for gold, diamonds, bauxite,
and iron ore pose a serious threat to aquatic and terrestrial habitats in some areas of
this ecoregion. Fires set by miners and agriculturalists can pose a threat to habitat if
they are uncontrolled. Unregulated tourism in Amerindian villages also adversely
impacts both the cultural and ecological richness of the area. Several hydroelectric
dams are currently being constructed, which threaten vast areas of savanna and
riparian habitat along the Caroni River. This series of 5 dams being constructed on
the Caroni River, and several others being planned on the Paragua River could be
devastating to riparian ecosystems and will flood several thousand square kilometers
of river basin.

Justification of Ecoregion Delineation

Delineation’s for this ecoregion were derived from several country specific vegetation
coverage maps, and blending was done along the borders according to expert
opinion. In Brazil delineation’s are according to the IBGE (1993) map, and the
linework follows the following vegetational coverage’s for the Amazon floristic
province: dense submontane ombrophilous forests and dense montane ombrophilous
forests. The small portion which extends into Guyana was derived by tracing the
logical continuation of the portion from Venezuela, and referenced with Huber et al.
(1995). Within Venezuela we used Huber’s (1995) map, and lumped the following
"evergreen forests" subregions: Tupuyes Meridionales, Sierra Parima, Tepuyes
Centro-Meridionales, Tepuyes Noroccidentales, Jaua-Maigualida, Caroní Medio,
Penillanura del Alto Paragua, and Piedemonte Noroccidental. In Brazil, we used the
IBGE (1993) vegetation map, and followed the delineation’s of "dense montane
ombrophilous forests" and "dense submontane ombrophilous forests" of the border
region with Venezuela. 

Delineation’s for this ecoregion were derived from several country specific vegetation coverage
maps, and blending was done along the borders according to expert opinion. In Brazil
delineation’s are according to the IBGE (1993) map, and the linework follows the following
vegetational coverage’s for the Amazon floristic province: dense submontane ombrophilous
forests and dense montane ombrophilous forests. The small portion which extends into Guyana
was derived by tracing the logical continuation of the portion from Venezuela, and referenced
with Huber et al. (1995). Within Venezuela we used Huber’s (1995) map, and lumped the
following "evergreen forests" subregions: Tupuyes Meridionales, Sierra Parima, Tepuyes
Centro-Meridionales, Tepuyes Noroccidentales, Jaua-Maigualida, Caroní Medio, Penillanura del
Alto Paragua, and Piedemonte Noroccidental. In Brazil, we used the IBGE (1993) vegetation
map, and followed the delineation’s of "dense montane ombrophilous forests" and "dense
submontane ombrophilous forests" of the border region with Venezuela. 


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