The Southern New Guinea lowland rain forests are some of the largest tropical wilderness areas in Australasia, with huge swaths of wet evergreen forest and important mosaics of other forest types. It is one of the richest areas for vascular plants in Indo-Malaysia.

Kikori Basin, Papua New Guinea. (Photograph by Don Henry)

Location and General Description

The Southern New Guinea lowland rain forests ecoregion stretches across the lowland forests south of the Central Cordillera of Indonesian Irian Jaya and Papua New Guinea (PNG). 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. The wettest portions of New Guinea are found in the Central Cordillera and from 100 to 1,000 meters (m) on the southern slopes of the Cordillera in this ecoregion. Although the remainder of the ecoregion is lower than most parts of New Guinea, the area's low relief and large rivers draining the nearby Central Ranges result in this ecoregion's inundation during the wet season. The wetland system associated with the Fly River is the largest watershed in PNG. Although New Guinea is a very active tectonic area with a complex geologic history, the geology of the West Papuan shelf, where this ecoregion is located, shows little folding, an indication of stability. The surface geology of the ecoregion consists of alluvium on active and relict alluvial plains and fans.

Source; WWF

The vegetation is primarily tropical lowland broadleaf forest, of both alluvial and hill type, in addition to a (17 percent) portion of savanna. Small (less than 10 percent each) percentages of semi-evergreen rain forest, tropical montane evergreen forest, limestone forest, peat swamp forest, and freshwater swamp forest are also present in the ecoregion.

Kikori Basin, Papua New Guinea. (Photograph by Don Henry)

The most extensive habitat in the 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 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, Dysoxylum, Syzygium, Vitex, Spondias, and Intsia. Although present, dipterocarps do not form extensive forests in New Guinea, as they do in Malaysia and Borneo. 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.

The lowland rain forests of this ecoregion are ecologically critical to the great Fly River watershed that is born in this high rainfall zone. The lowland hill forests are dominated by Hopea celtidifolia and Vatica russak, whereas the lower montane elements include Podocarpus and Lithocarpus. The Upper Fly lowlands, except for extensive settlements around the Ok Tedi mine in the west, represent a large expanse of sparsely populated, old-growth wet rain forest that is characteristic of the extraordinarily rich biota of the Upper Fly platform. This ecoregion also includes an enormous extent of botanically unknown tower limestone as well as Araucaria forest, Castanopsis, Quercus, traditional medicinal and food plants, nutmeg, and traditional spirit trees.

Lake Kutubu, PNG's largest lake, is also found in this ecoregion. This lake supports a diverse aquatic plant flora, and eleven of its fourteen fish species are endemic to it.

Biodiversity Features

Overall richness and endemism for this ecoregion are low to moderate when compared with those of other ecoregions in Indo-Malaysia, although plant richness is high.

The mammalian fauna consists of a wide variety of tropical Australasian marsupials, including a tree kangaroo. The ecoregion contains sixty-nine mammal species, thirteen of which are endemic or near endemic (Table 1). Bulmer's fruit bat (Aproteles bulmerae) and the large pogonomelomys (Pogonomelomys bruijni) are critically endangered, whereas the lesser tube-nosed bat (Nyctimene draconilla), New Guinea sheathtail-bat (Emballonura furax), Fly River horseshoe-bat (Hipposideros muscinus), and Papuan mastiff bat (Otomops papuensis) are considered vulnerable.

The avifauna of the ecoregion has a clear Australasian flavor, including representatives of several Australasian families such as Ptilonorhynchidae, Eopsaltridae, Meliphagidae, and Paradisaeidae. There are 344 bird species in the ecoregion, including 5 endemic and near-endemic species (Table 2). The ecoregion intersects two separate Endemic Bird Areas (EBAs), the South Papuan lowlands and the Trans Fly.

Current Status

The Papuan Plateau and the Purari River Basin are major wilderness areas in this ecoregion. Most of the habitat remains in contiguous blocks, and the three protected areas, which cover 9,330 square-kilometers (km²), or 8 percent of the ecoregion area, are well distributed between Indonesia and PNG (Table 3). All the protected areas are large (more than 1,000 km²). An additional large protected area (Kumbe-Merauke, 1,268 km²) also extends into this ecoregion.

Types and Severity of Threats

Northern cassowary (''Casuarius unappendiculatus''). (Photograph by Don Henry)

The ecoregion suffers from the potential major threat of logging, and several large timber concessions are allotted throughout the ecoregion. Additional threats include traditional agriculture and expansion of subsistence coffee areas. Traditional hunting for the Raggiana bird-of-paradise for sale and trade also occur.

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 evergreen forests to the south of the Central Cordillera were placed in the Southern New Guinea lowland rain forests, and the extensive freshwater swamp forests were placed in the Southern New Guinea freshwater swamp forests. The freshwater swamp forests in the southern Vogelkop were also included in this ecoregion. 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