Introduction

Associated with the foothills north of the Central Ranges and some of New Guinea's great lowland river systems, the Northern New Guinea lowland and freshwater swamp forests are an extensive, continuous tropical lowland and swamp forest that is still largely unexplored.

Location and General Description

Mamberamo-Pegunungan Foja Reserve, Indonesia. (Photograph by WWF-Canon/Ian Craven)

This ecoregion is made up of the lowland, freshwater, and peat swamp forests of Irian Jaya and Papua New Guinea (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. Northern New Guinea is a very active tectonic area with a complex geologic history. 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. The surface geology of this ecoregion consists of clastic sedimentary rocks and recent alluvium. 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. 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 meters (m) or less, and many of these are associated with the Sepik River.

Madang, Papua New Guinea. (Photograph by David Olson)

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. Palms may be common in the shrub layer. 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. 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.

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.

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. 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.

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. 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.

Grass habitats are dominated by Leersia, Phragmites, and Saccharum.

Biodiversity Features

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 (Table 1). The lesser tube-nosed bat (Nyctimene draconilla) and greater sheath-tailed bat (Emballonura furax) are considered vulnerable. The western part of the ecoregion is the only known site in PNG for the western ringtail possum (Pseudocheirus albertisi).

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 Endemic Bird Area (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 (Table 2). Salvadori's fig-parrot (Psittaculirostris salvadorii) is considered vulnerable.

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.

Current Status

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 (Table 3).

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.

Justification of Ecoregion Delineation

Using Whitmore's map of the vegetation of Malesia and MacKinnon's 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, and the montane forests were placed in the Northern New Guinea montane rain forests. This ecoregion corresponds to MacKinnon's biounits P3e and P3j. Udvardy placed these ecoregions in the Papuan biogeographic province of the Oceanian Realm.

Additional information on this ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
• World Wildlife Fund Homepage