Venezuelan Amazon Research Articles

Fire in the Venezuelan Amazon 2: Environmental Conditions Necessary for Forest Fires in the Evergreen Rainforest of Venezuela

We studied the potential for forest fires in seven vegetation types near San Carlos de Rio Negro, Venezuela, one of the wetter regions of Amazonia. Three of the communities were tall, closed-canopy forests; two communities had closed canopies but were short in stature; and two communities had open canopies. Fine fuels reached dynamic equilibrium moisture levels (i.e., no further net drying given prevailing microclimate) after only three to four rainless days in the two open-canopy and two short-stature communities and after eight to ten days in the three tall, closed-canopy forest types. Fine-fuel moisture content at 'equilibrium' was generally twice as high in the tall, closed-canopy forest as in the other four vegetation types (20% vs 10%). We successfully started surface fires in the two open-canopy and two short-stature communities after four to six days without rain. An average of 19-27% of the available fuels were consumed by these fires. We were unable to burn the three tall, closed-canopy forest communities, even after artificially excluding rain for 41 days. The elevated relative humidities characteristic of tall, closed-canopy forests do not permit fuels to dry to the combustion point. Under current climatic conditions, fire is only possible if the relative humidity drops to 65% or below. In some open-canopy and short-stature communities, relative humidity falls below this threshold about one day each week, on average, but in tall, closed-canopy forest such levels may occur less than one day each year.

Ritual production of environmental history among the Arawakan Wakuénai of Venezuela

This essay examines ritual and ceremonial activities among the Arawakspeaking Wakuenai of the Venezuelan Amazon as processes of constructing power relations in changing historical and ecological conditions. Ritual evocations of the vertical dimension of power relations between mythic ancestors and human descendants adapt local populations to conditions of relatively severe stress, such as epidemics and scarcity of fish in long wet seasons. Other rituals evoke the horizontal dimension of power relations between affinally-related groups as a way of expanding the local descent group in conditions of lowered stress. These two ways of exercising ritual power link human populations to specific natural habitats and provide flexibility needed to adjust to demographic and other historical changes. Through ritual performances, the Wakuenai transform the natural environment into a cultural landscape of socialized objects and, conversely, remember the history of political relations among peoples through spirit-naming of natural species, objects, places, and geographic landmarks.

The phlebotomine sandflies of Venezuelan Amazonia.

Phlebotomine sandflies were surveyed in two ecologically contrasted areas, the northern moist and southern wet tropical forests, of the Territorio Federal Amazonas, Venezuela. Three new taxa and twenty-one new records were added to the previously known species list for Venezuelan sandflies, which now totals eighty species. Both sexes of Lutzomyia (Psychodopygus) killicki sp.n., L. (Trichophoryomyia) bettinii sp.n., L. (Nyssomyia) olmeca reducta subsp.n. and and the females of L. bernalei Osorno et al., Brumptomyia pintoi Costa Lima and L. begonae (Ortiz & Torres) are described and illustrated.

Amazon diversity in light of the paleoecological record

Disjunct distributions of Amazonian species have been explained previously by a refugial theory which postulates that Amazonian rain forest was preserved in large highland regions throughout the Pleistocene. No direct, radiocarbon dated evidence exists for the last glacial maximum with which to test this theory. The only radiocarbon dates of Pleistocene age from the Amazon basin are of fossiliferous deposits in the proposed Napo refugium of the West, where both pollen assemblages and wood samples indicate that forest with cool Andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation, implying a temperature depression of at least 4°C in the Amazon lowlands. Under modern climatic conditions, lateral erosion by river meander, together with surface erosion, serves as a rejuvenating mechanism for the rain forests of Peru and Ecuador. The instability of late Holocene Amazonian climates is demonstrated by documenting a precipitation event in the eastern Andean cordillera that caused widespread flooding of western Amazonian forests 800–1300 BP. Late Holocene pollen histories from widely dispersed parts of central Amazonia distinguish between vegetation histories in the drainage of northern, south-western and western watersheds, but all show histories of fluctuating intensities of dry seasons. Radiocarbon dating of charcoal layers in soils of Venezuelan Amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka. The high species richness of Amazonia is a result of numerous opportunities for vicariance because of a very large total area, wide variety of habitats and intermediate levels of disturbance, particularly by hydrological processes, that has varied on timescales from years to millennia. Amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times.

Amazon Diversity in Light of the Paleoecological Record

Disjunct distributions of Amazonian species have been explained previously by a refugial theory which postulates that Amazonian rain forest was preserved in large highland regions throughout the Pleistocene. No direct, radiocarbon dated evidence exists for the last glacial maximum with which to test this theory. The only radiocarbon dates of Pleistocene age from the Amazon basin are of fossiliferous deposits in the proposed Napo refugium of the West, where both pollen assemblages and wood samples indicate that forest with cool Andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation, implying a temperature depression of at least 4°C in the Amazon lowlands. Under modern climatic conditions, lateral erosion by river meander, together with surface erosion, serves as a rejuvenating mechanism for the rain forests of Peru and Ecuador. The instability of late Holocene Amazonian climates is demonstrated by documenting a precipitation event in the eastern Andean cordillera that caused widespread flooding of western Amazonian forests 800–1300 BP. Late Holocene pollen histories from widely dispersed parts of central Amazonia distinguish between vegetation histories in the drainage of northern, south-western and western watersheds, but all show histories of fluctuating intensities of dry seasons. Radiocarbon dating of charcoal layers in soils of Venezuelan Amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka. The high species richness of Amazonia is a result of numerous opportunities for vicariance because of a very large total area, wide variety of habitats and intermediate levels of disturbance, particularly by hydrological processes, that has varied on timescales from years to millennia. Amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times.