Orinoco Delta swamp forests
The Orinoco Delta Swamp Forests occur in a diverse and porous matrix of coastal
vegetation types along the river delta and
surrounding regions of northwestern
Venezuela and northeastern Guyana. These inundated forests are have moderate species
richness, and provide habitat to a number of
endangered and endemic species. Much of
this region is still intact due to its inaccessibility and poor soils, however
recently oil exploration and extraction projects
have encroached into these once pristine
Location and General Description
The Orinoco Delta Swamp Forests ecoregion occurs in a continuous expanse
from the southern reaches of the Paria Peninsula in northern Venezuela, extending southwards along the coastal floodplains
of the Orinoco Delta to the Waini River in Guyana. The western and northern
boundaries and are delineated by mangroves and the Atlantic Ocean, while the
eastern boundary occurs along a precipitation gradient - bordering xeric scrub and
scrublands in the north, llanos and wetlands in the central portions, and moist forests
in the south.
Climate in this region is tropical, hot and humid. Precipitation varies throughout the region, and
fluctuates between 500-2000mm annually, becoming increasingly wetter and more humid moving
south. Rainfall is irregular and the wet season begin in April/May and usually last through
December. Temperatures average 26 C, becoming slightly cooler at night.
Geographically this is a landscape of little relief. Elevations typically average one meters, but
reach as high as 9 meters in the highest terra firma levies south of the delta region. The soils in
this ecoregion are almost entirely alluvial deposits, originating as far away as the northern
Andes of Colombia and Venezuela.
These swamp forests are characteristically impregnated with river systems and hosts a great
diversity of riparian features including permanent wetlands and marshes (Orinoco wetlands
ecoregion), large rivers, oxbows lakes, small gallery streams, levies, and the typical delta alluvial
fan. The delta itself consists of increasingly partitioned distributions which become more
confined and disjunct as they diverge from the main channel, then come together again as they
move east towards the Atlantic Ocean. In so doing these numerous rivers form a great number
This swamp forest ecoregion is heavily influenced by, and in some areas characterized by the
local river systems - particularly in the Orinoco Delta region. According to the broad vegetation
classification of UNESCO (1981), the core of this ecoregion falls under the classification of
tropical ombrophilous swamp forest. The predominant vegetation in this region are
hydrophilous trees and palms, with abundant epiphytes and scattered herbaceous layer.
Hardwood trees include Carapa guianensis, Ceiba pentandra, Dimorphandra excelsa,
Hirtella triandra, Inga punctata, Mainilkara globosa, Ocotea rodioei, Pentaclethera
filamentosa, Pterocarpus officinalis, Symphonia globulifera, and Terminalia obovate.
Numerous palms occur here as well, and often in monotypic stands. These include Astrocaryum
aculeatum, Euterpe oleraceae, Manicaria succifera, and Mauritia flexousa.
The swamp forests of the Orinoco (Amacuro) Delta are important wildlife habitats
and are known to support a number of endemic plant species (Dinerstein et al.
1995). Swamp forests are the dominant vegetation feature of the Orinoco Delta
(IUCN 1996), and the ecoregion is embedded in a complex matrix of wetlands,
mangroves, and both inundated and terra firma moist forest. These swamp forests
are characterized by permanently inundated forests and abundant waterways and
These swamp forests provide important habitat for a number of threatened and endangered
species such as the Orinoco crocodile (Crocodylius intermedius CR), Amazon river dolphin
(Inia geogffrensis VU), jaguar (Panthera onca LR), bush dog (Speothos venaticus VU), giant
river otter (Pteronura brasiliensis EN), Orinoco goose (Neochen jubata LR), and the harpy
eagle (Harpia harpyja LR) (Eisenberg 1989; IUCN Red List Database).
The swamp forests of eastern Venezuela are, as a whole, relatively intact. Heavy
regional exploitation is a threat in the northern areas where population pressures are
higher. Three protected areas exist which protect portions of this ecoregion, two
national parks and one forest reserve. Two indigenous areas also occur, but offer
lesser protection and are readily exploited.
The following protected areas include portions of this ecoregion but also include sections of
the surrounding ecoregions: the Guianan mangroves, Guianan moist forests, and the Orinoco
wetlands. The Delta del Orinoco biosphere reserve (9¸21'N - 60¸56'W) was gazetted in 1991 by
WCMC & UNEP, and is the largest protected area within the delta region. This national
biosphere reserve has been given IUCN category VI status and covers an area of 876,500 ha -
only portions of which are represented by this wetlands ecoregion. The Delta del Orinoco
National Park (9¸25'N - 61¸30'W), gazetted in 1992, also offers protection and with increasing
levels of enforcement. This national park is given IUCN Category II status and covers an area of
331,000 ha (UNEP/WCMC Database).
The Imataca Forest Reserve (8¸20'00N - 59¸55'00W), gazetted in 1961, has been given an IUCN
Category VI status, and encompasses these swamp forests south of the Orinoco River. This
3,203,250 ha reserve is among the largest in Venezuela - however this ecoregion is only
represented in its eastern coastal portions. Turuïpano National Park (10¸34'N - 62¸43'W),
gazetted in 1991 protects portions of the northern extent of this ecoregion. This 72,600 ha park
is given an IUCN Category II status. Finally, Mariusa National Park (9¸30'00N - 61¸30'00W )
along the northern coastal delta offers protection to some of the smaller outliers of this
ecoregion, especially along the Maracao River. This 265000 ha park has an IUCN category II
status was gazetted in 1991.
Types and Severity of Threats
The greatest threat to this region is currently oil exploration and extraction, which
posses a serious threat to much of the Orinoco Delta and surrounding regions. The
threats imposed by oil extraction are multifaceted, and begins with the exploration
phases which opens up the area. Once extraction begins settlement and human
population pressures increase, which have the effect of increasing hunting, small scale
forest clearing for subsistence and materials, and displacement and corruption of the
indigenous Warao peoples.
Secondarily is water diversion and containment, which disrupts the seasonal cycles of the
Orinoco River and its tributaries. Portions of this wetland ecoregion have been severely altered
as a consequence of a flood control program initiated in the 1960s when the Caño Mánamo was
dammed. The reduced water levels in the upper delta have caused the region to become tidal,
and as a result the water levels now rise and fall by 1-2m daily. This has also caused the salinity
levels to increase dramatically which has in turn influenced the flora and fauna which are able to
survive in these swamp forests as well as the surrounding rivers and tributaries.
Palm exploitation is a major problem in some areas, and commercially used species such as
Euterpe oleraceae and Mauritia flexuosa are often heavily exploited in the more accessible
regions (IUCN 1996). Timber extraction potential is poor (World Bank 1998), however threats
from this resource exploitation are compounded by the important role the target species play in
maintaining the fragile ecosystems. Soil quality is also poor and does not support agriculture.
Logging is becoming a growing concern.
Justification of Ecoregion Delineation
These seasonally inundated forests occur from the Araya-Paria delta and extend
southwards along Atlantic Venezuela, across the Orinoco delta, and into northern
Guyana. These forests are distinct in their vegetation, which is adapted to seasonal
and permanent inundation – and several endemic species are present. Eastern
linework follows the transition from coastal mangrove to moist forest, and is
interspersed with permanent and seasonal open and semi-open wetlands. Within
Venezuela, linework follows Huber and Alarcon (1988) classification of the "delta
lowland and coastal swamp" subregion (B.3). Portions extending into Guyana
roughly follow the Huber et al. (1995) classification of "low, evergreen, seasonal
flooded swamp and marsh forest".