Location and General Description
The Rio Napo region is situated at the western extreme of Amazonia where it hosts extraordinarily rich tropical moist forests. The ecoregion covers the northwestern portion of Peru, the Amazon region of Ecuador and the southwestern corner of Colombia’s Amazon. It is bounded on the west by the foothills of the Andes Mountains, on the south by the Marañon River in Peru, on the north by the Napo in Peru and the Caguán in Colombia. The region extends east almost to the Peruvian City of Iquitos near the confluence of the Napo and Amazon Rivers. Many important Amazon rivers including the Morona, Pastaza, Tigre, and Curaray in Ecuador and Peru, and the headwaters of the Caquetá and Putumayo in Colombia bisect the region. All of these rivers drain into the Amazon Basin.
During geologic history, the Napo moist forest region has been a place of invasion and counter invasion of species coinciding with dramatic changes in temperature and humidity. These climatic fluctuations probably resulted in high rates of evolution and speciation, thereby rendering this area extremely biodiverse. The Santa Cecilia area in northwestern Ecuador is a region of postulated fluvial perturbations (extensive river meanders) which may have been responsible for disjunctions in the distributions with some species . The topography of the region has a slightly inclined platform; 300 to 400 m elevation in the west grading to 100 m elevation in the east. The northern part of the region is low plains with hills that rise only 10 m above the level of the river. The climate is humid tropical, with a subtle dry season. Mean annual temperature is 26° C, but monthly temperature ranges from 12 to 38° C depending on the time of year, elevation, and latitude. This ecoregion contains some of the highest annual precipitation in Amazonia. With the extreme western parts of the region receiving up to 4,000 mm, and 2,500-3,000 mm in the eastern reaches. Older soils from the Guayana Shield intermingle with the more recent Quaternary sediments from the Andes region producing heterogeneous soils.
Three main types of vegetation occur in this moist forest ecoregion: (1) terra firme forest on the high relief, not subject to flooding; (2) várzea forest type, subject to seasonal flooding by whitewater rivers (major portions of várzea are classified with Iquitos Várzea ecoregion); and (3) igapó forest type, on poor soils subject to seasonal or permanent flooding by blackwater rivers (no sediment load). In general these are all tall moist evergreen tropical rain forests. The terra firme forests are more diverse and generally taller with canopies reaching 40 m, and emergent trees to 50 m in height; epiphytes and lianas occur here but are not abundant. Along the rivers, some stands are dominated by palms especially Mauritia flexuosa and swamp forests with a distinct flora form parts of the adjacent upland forests. In an igapó forest of Ecuador, Gentry (1988) found 149 tree species in a single hectare compared to 244 species on the adjacent terra firme. These moist tropical, terra firme forests harbor species such as Macrolobium acaciifolium, Coussapoa trinervia, Licania sp., Eugenia sp., Vismia baccifera, Guarea sp., Nectandra cf. reticulata, Cedrelinga catenaeformis, Erisma uncinatum, Phragmotheca ecuadoriensis, Parkia multijuga, Ochroma sp., and Pouteria sp., and palm species of the genera Bactris and Astrocaryum. The most abundant species in this forest type is the subcanopy palm Iriartea deltoidea. Important families also included are Meliaceae, Arecaceae, Moraceae, Leguminosae, Myristicaceae, and Rubiaceae. Along the blackwater Rio Nanay corridor in Peru, a distinct flora is found with Symmeria, Mollia, and Caryocar microcarpum although not known elsewhere on the terra firme. The western portion of this region has high palm diversity; hosting the Andean region endemic's including Prestoea schultzeana, Phytelaphas tenuicaulis, and Wettinia drudei . Many important timber species are found here, such as mahogany (Swietenia macrophylla), tropical cedar (Cedrela odorata), and kapok (Ceiba pentandra).
The two other forest types although water-saturated also support a diverse vegetative layer with plants and trees that are adapted to the watery conditions. For further information and detail on flooded forests, see the corresponding várzea ecoregion descriptions.
Some 219 species of mammals and 649 species of birds are reported for the ecoregion. At the Cuyabeno Reserve in northeastern Ecuador, 313 species of trees have been identified in one hectare, and 500 species of birds and 100 species of mammals have been reported.
Representative mammals include Brazilian tapirs (Tapirus terrestris), collared peccaries (Tayassu tajacu), woolly monkeys (VU) (Lagothrix lagotricha), long-haired spider monkeys (Ateles belzebuth), brown pale-fronted capuchins (Cebus albifrons), monk sakis (Pithecia monachus), giant armadillos (VU) (Priodontes giganteus), agoutis (Dasyprocta sp.), pacas (Cuniculus paca), capybaras (Hydrochaeris hydrochaeris), two-toed sloths (Choloepus sp.), three-toed sloths (Bradypus sp.), southern coatis (Nasua nasua), jaguars (Panthera onca), pumas (Puma concolor), ocelots (Leopardus pardalis), jaguarundis (L. yagouaroundi), margays (L. wiedii) (V), giant otters (Pteronura brasiliensis), red brockets (Mazama americana), brown brockets (M. gouazoubira), Amazonian manatees (Trichechus inunguis), and Amazon River dolphins (Inia geoffrensis).
Among the avifauna, harpy eagles (Harpia harpyja), curassows (Mitu selvini), and white-browned guans (Penelope jacucaca) are found. This ecoregion falls with in the Upper Amazon-Napo lowlands endemic bird area. According to Stattersfield (1998) the bird distributions in this ecoregion are poorly known. Restricted range species however, are thought to include olive-chested flycatcher (Myiophobus cryptoxanthus), brown nunlet (Nonnula brunnea), and Ochre-striped antpitta (Grallaria dignissima) to name a few (Stattersfield 1998).
The Yasuni Biosphere Reserve in Ecuador hosts 96 species of reptiles. Of these species, 53 are snakes, including the lethal bushmaster (Lachesis muta), three species of pit viper (Bothrops spp.), boa constrictors (Boa constrictor) and emerald tree boas (Carallus caninus). Other reptiles include endangered South American River turtles (Podocnemis expansa), yellow-footed tortoises (Geochelone denticulata), spectacled caiman (Caiman crocodylus), dwarf caiman (Paleosuchus palpebrosus), and black caiman (Melanosuchus niger). Many aquarium fish are found here including arawana (Osteoglossum bichirrosum) and various tetras (Hyphaessobrycon, Bryconops). Two species of fierce piranha (Serrasalmus) and stingrays (Potamotrygon motoro) also inhabit these rivers.
Several large protected areas are situated within the Napo moist forest ecoregion; however for the most part their administration suffers from insufficient funding. The Cuyabeno Wildlife Reserve (6,034 km2) in Ecuador is an area important for scientific research and habitat protection; it is now threatened by petroleum operations. Limoncocha Biological Reserve and Yasuni National Park (6,797 km2) are important protected areas, the latter being home to many Amazonian Amerindians. La Paya National Park in Colombia is situated on the interfluve between the Caquetá and Putumayo Rivers, but its forests and species are under threat from colonization, plantation agriculture, and hunting in and around the reserve. The entire area around La Paya National Park is deforested. The large triangle between the Caguán and Upper Putumayo Rivers in Colombia and the province of Napo in Ecuador at the northern extent of the ecoregion are areas of notable deforestation, resulting from forest conversion to cattle pasture and coca (Erythroxylum coca) plantations. The remaining intact Napo moist forest is considered threatened by degradation resulting from ongoing human activities.
Types and Severity of Threats
The whole Ecuadorian Amazon has been subject to oil and gas exploration and virtually all of the Napo riverine area in Ecuador is open for oil leasing, according to Stattersfield (1998). The construction of roads by oil companies has resulted in deforestation, displacement of the indigenous peoples, and colonization of the interior by peasant farmers. Major deforestation also results from cattle ranching and coca production, and it has destroyed habitat of the richest herpetofauna in the world . Ongoing human activities such as logging, ranching, large-scale agriculture, mining, wildlife trade, and industrial development threaten these forests and the species they harbor.
Future conservation actions should protect the hydrological basins rich in wildlife and natural resources and their traditional indigenous communities, enforce existing legislation protecting conservation areas, control the illegal traffic of wild animals such as ornamental aquarium fish, and develop and implement species conservation action plans.
Justification of Ecoregion Delineation
Deliniations for the Napo moist forests were derived from riparean and elevational boundaries which significantly influence species distributions, many of which have restricted ranges confined to this ecoregion. The southern boundary of this ecoregion follows the Marañon from the foothills of the Andes westward to the Solimões (Amazon) until the confluence with the Napo River. The eastern boundary follows the Napo River northwards, then breaks off from this and extends northwards until it reaches the Guayas River, where it follows this waterway until it reaches the foothills of the Andes. The linework for the aformentioned deliniations was derived from pleistocene forest refugia proposed by Prance (1973) and on regions of butterfly endemism (Brown 1987). Final linework was reviewed and at an ecoregional workshop of the Northern Andes (Bogota, Colombia, 24-26, July, 2000). For linework in Ecuador we referned to Sierra (1999). This ecoregion falls within the greater "Amazon tropical forest" of Peru in national classifications (Instituto Geográfico Nacional 1987).
Brown, K.S. 1987. Biogeography and evolution of Neotropical Butterflies. Pages 66-104 in T. Whitemore, and G. Prance, editors, Biogeography and quaternary history in Tropical America. Oxford Science Publications.
Complejo Ecoregional de los Andes del Norte (CEAN). Experts and ecoregional priority setting workshop. Bogota, Colombia, 24-26, July, 2000.
Duellman, W. E. 1990. Herpetofauna in Neotropical rainforests: comparative composition, history, and resource use. Pages 455-505 in A. H. Gentry, editor, Four neotropical forests. New Haven: Yale University Press.
Gentry, A. 1988. Changes in plant community diversity and floristic composition on environmental and geographical gradients. Annals of the Missouri Botanical Garden 75: 1-34.
Henderson, A. 1995. The Palms of the Amazon. New York: Oxford University Press.
Instituto Geográfico Nacional. 1987. Ecoregiones del Peru. Map 1:5,000,000. Atlas del Peru, Lima, Peru.
Prance, G. 1989. Phytogeographic support for the theory of Pleistocene forest refuges in the Amazon Basin, based on evidence from distribution patterns in Caryocaracaceae, Chrysobalanaceae, Dichapetalaceae, and Lecythidaceaea. Acta Amazonica 3, 5-28.
Sierra, R., editor. 1999. Propuesta Preliminar de uns Sistema de Clasificación de Vegetación para el Ecuador Continental. Proyecto INEFAN/GEF-BIRF y EcoCiencia. Quito, Ecuador
Strattersfield, A. J., M. J., Crosby, A. J. Long, and D.C. Wege. 1998. Endemic bird areas of the World, priorities for biodiversity conservation. Cambridge, UK: BirdLife International.
Prepared by: Robin Sears, César Marín, and Jan Schipper
Reviewed by: In process