Location and General Description
This ecoregion is made up of the lowland, freshwater, and peat swamp forests of Irian Jaya and PNG, from the foothills of the northern side of the Central Cordillera to the north coast of the island of New Guinea. The climate of the ecoregion is tropical wet, which is characteristic of this part of Melanesia, located in the western Pacific Ocean north of Australia (National Geographic Society 1999). Northern New Guinea is a very active tectonic area with a complex geologic history (Bleeker 1983). The Lakes-Plains depression, which forms this ecoregion, is squeezed between the foothills of the Central Cordillera to the south and the Van Rees and Foya Mountains to the north (Petocz 1989). The surface geology of this ecoregion consists of clastic sedimentary rocks and recent alluvium (Petocz 1989). The ecoregion is centered on three large river basins: the Mamberamo, Taritatu, and Tariku river basin in Irian Jaya and the Sepik and Ramu river basins in PNG. The Sepik River, one of the two largest watersheds in PNG, supports a large human population that is heavily dependent on the river (Miller et al. 1994). Although there is extensive area in the upper basins, large portions of the mainstems of these rivers flow through broad alluvial valleys, which consist of extensive wetland areas. Twenty-one of PNG's twenty-four largest lakes are found at elevations of 40 m or less, and many of these are associated with the Sepik River (Osborne 1993).
The lowland forests and freshwater swamps of this ecoregion contain diverse habitats, including lowland and hill forest, grass swamps, swamp forests, savannas, and woodlands. The most extensive habitat in this ecoregion is lowland broadleaf evergreen forest, which can be divided coarsely into alluvial and hill forest. Lowland alluvial forest has a canopy that is multitiered and irregular, with many emergents. The forest understory contains a shrub and herb layer with a variety of climbers, epiphytes, and ferns (Petocz 1989). Palms may be common in the shrub layer (Paijmans 1975). The very mixed floristic composition of the canopy trees includes Pometia pinnata, Octomeles sumatrana, Ficus spp., Alstonia scholaris, and Terminalia spp. Additional important genera include Pterocarpous, Artocarpus, Planchonella, Canarium, Elaeocarpus, Cryptocarya, Celtis, Dracontomelum, Sysoxylum, Syzygium, Vitex, Spondias, and Intsia (Paijmans 1975). The somewhat lower-canopy, more closed lowland hill forest contains more open shrub layer but a denser herbaceous layer. Palms are fewer in number. The dominant canopy trees include species of Pometia, Canarium, Anisoptera, Cryptocarya, Terminalia, Syzygium, Ficus, Celtis, Dysoxylum, and Buchanania. Koompassia, Dillenia, Eucalyptopsis, Vatica, and Hopea are locally abundant. Dense stands of Araucaria, the tallest tropical trees in the world, are present in scattered locations (Paijmans 1975; Nightingale 1992).
Because of its large geographic extent, this ecoregion is subject to local variation. In the Central Range and Sepik foothills, extensive stands of Agathis labillardieri support a highly diverse epiphytic fauna. The Ramu Basin supports extensive areas of lowland rain forest and swamp forest, some of which are developed on ultrabasic parent rock (Miller et al. 1994).
Lowland swamp forests are extensive in the northern lowland portions of the island, associated with low-gradient river systems such as the Sepik River. The water table is near or above the ground surface but may fluctuate widely. Much of the forest along the rivers is subject to inundation (Paijmans 1975; Davis et al. 1975). A dynamic environment such as these freshwater wetlands contains a mosaic of habitats. One list of the subhabitats of lowland freshwater swamps includes herbaceous swamp vegetation, Leersia grass swamp, Saccharum-Phragmites grass swamp, Pseudoraphis grass swamp, mixed swamp savanna, Melaleuca swamp savanna, mixed swamp woodland, sago swamp woodland, pandan swamp woodland, mixed swamp forest, Campnosperma swamp forest, Teminalia swamp forest, and Melaleuca swamp forest (Osborne 1993).
The structure of swamp forests ranges from very small-crowned to medium-crowned, dense to open, with a 20- to 30-m canopy of an even height. Sago palm (Metroxylon sagu) and Pandanus spp. generally are present in the subcanopy. Canopy trees of the swamp forest include Campnosperma brevipetiolata, C. auriculata, Terminalia canaliculata, Nauclea coadunata, and Syzygium spp., with Myristica hollrungii in delta areas. However, whereas some swamp forests are almost pure stands of Campnosperma or Melaleuca, others are species-rich, and many other tree species are possible (Paijmans 1975). The canopy along the Mamberamo River is about 45 m high and includes Ficus and Pittosporum ramiflorum. Other inundated forests include Timonius, Dillenia, and Nauclea (Davis et al. 1995).
Grass habitats are dominated by Leersia, Phragmites, and Saccharum (Petocz 1989).
Generally, this ecoregion exhibits low to moderate richness and endemism when compared with those of other ecoregions in Indo-Malaysia. Reptile and amphibian richness is thought to be high but is poorly documented.
The mammalian fauna consists of a wide variety of tropical Australasian marsupials, including tree kangaroos. The seventy-six mammal species in this ecoregion include thirteen species that are endemic or near endemic (Flannery 1995; Flannery and Groves 1998; Bonaccorso et al., in press) (table 1). The lesser tube-nosed bat (Nyctimene draconilla) and greater sheath-tailed bat (Emballonura furax) are considered vulnerable (IUCN 2000). The western part of the ecoregion is the only known site in PNG for the western ringtail possum (Pseudocheirus albertisi) (Beehler 1994).
Table 1. Endemic and Near-Endemic Mammal Species.
Perorictidae Echymipera clara
Perorictidae Echymipera echinista
Macropodidae Dorcopsis hageni*
Macropodidae Dorcopsis muelleri
Pteropodidae Nyctimene draconilla
Emballonuridae Emballonura furax
Rhinolophidae Hipposideros wollastoni
Rhinolophidae Hipposideros edwardshill*
Vespertilionidae Kerivoula muscina
Molossidae Otomops secundus
Muridae Paraleptomys rufilatus
Muridae Hydromys hussoni
Muridae Pogonomelomys mayeri
An asterisk signifies that the species' range is limited to this ecoregion.
The avifauna of the ecoregion has a clear Australasian flavor, including representatives of several Australasian families such as Ptilonorhynchidae, Eopsaltriidae, Meliphagidae, and Paradisaeidae. This ecoregion corresponds very well with the North Papuan lowlands EBA, which has nine restricted-range bird species, including five species found nowhere else on Earth. All told, the ecoregion contains sixteen endemic or near-endemic species (Stattersfield et al. 1998; Beehler et al. 1986; Coates 1985) (table 2). Salvadori's fig-parrot (Psittaculirostris salvadorii) is considered vulnerable (IUCN 2000).
Table 2. Endemic and Near-Endemic Bird Species.
Family Common Name Species
Psittacidae Edwards's fig-parrot Psittaculirostris edwardsii
Psittacidae Salvadori's fig-parrot Psittaculirostris salvadorii
Loriidae Brown lory Chalcopsitta duivenbodei
Apodidae Papuan swiftlet Aerodramus papuensis
Alcedinidae Red-breasted paradise-kingfisher Tanysiptera nympha
Corvidae Brown-headed crow Corvus fuscicapillus
Monarchidae Rufous monarch Monarcha rubiensis
Monarchidae Rufous-collared monarch Arses insularis
Pachycephalida White-bellied whistler Pachycephala leucogastra
Cinclosomatidae Brown-capped jewel-babbler Ptilorrhoa geislerorum
Eopsaltriidae Green-backed robin Pachycephalopsis hattamensis
Meliphagidae Silver-eared honeyeater Lichmera alboauricularis
Meliphagidae Brass's friarbird Philemon brassi*
Paradisaeidae Jobi manucode Manucodia jobiensis
Paradisaeidae Pale-billed sicklebill Epimachus bruijnii*
Paradisaeidae Greater melampitta Melampitta gigantea
An asterisk signifies that the species' range is limited to this ecoregion.
A small portion of the ecoregion, along the lower Mamberamo River, is part of the Mamberamo-Pegunungan Jayawijaya Centre of Plant Diversity in Irian Jaya (Davis et al. 1995).
This ecoregion is still largely undisturbed. There are some transmigration sites in the lowland forest on the Indonesian side near Nabire and Jayapura. Nineteen percent of the ecoregion is covered by protected areas, mostly in Indonesia (MacKinnon 1997) (table 3).
Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area Area (km2) IUCN Category
Unnamed [AA0116] 3,190 ?
Mamberamo-Pegunungan Foja [AA0116] 9,130 IV
Foja (extension) 6,760 PRO
Cape Wom International Memorial Park 50 UA
Sepik River 3,850 ?
Yakopi Nalenk Mountains [AA0105] 2,180 ?
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
Types and Severity of Threats
A large dam has been proposed for the Mamberamo Gorge, and timber and agricultural activities are a potential threat. A planned highway between Jayapura and Wamena is a threat because of improved access (Stattersfield et al. 1998).
Justification of Ecoregion Delineation
Using Whitmore's (1984) map of the vegetation of Malesia and MacKinnon's (1997) reconstruction of the original vegetation, we delineated the large areas of distinct habitat types as ecoregions. The tropical lowland moist and freshwater swamp forests to the north of the Central Cordillera were placed in the Northern New Guinea Lowland Rain and Freshwater Swamp Forests [AA0115], and the montane forests were placed in the Northern New Guinea Montane Rain Forests [AA0116] (based largely on recommendations by Bob Johns, pers. comm., 1999). This ecoregion corresponds to MacKinnon's (1997) biounits P3e and P3j. Udvardy (1975) placed these ecoregions in the Papuan biogeographic province of the Oceanian Realm.
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: John Morrison
This text was originally published in the book Terrestrial ecoregions of the Indo-Pacific: a conservation assessment from Island Press. This assessment offers an in-depth analysis of the biodiversity and conservation status of the Indo-Pacific's ecoregions.