Southeastern Asia: Southern portion of the island

The Trans Fly Savanna and Grasslands [AA0708] ecoregion is one of the most extensive lowlands on the island of New Guinea. Its seasonally dry climate is unusual for the island of New Guinea and more like that of northern Australia. The habitats in this ecoregion are still relatively intact.

  • Scientific Code
  • Ecoregion Category
  • Size
    10,300 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Location and General Description
This ecoregion is made up of the monsoonal savanna and grassland habitat along the southern coast of New Guinea, in both Indonesia and PNG. The climate of the ecoregion is strongly seasonal tropical dry, a climate that only this portion of New Guinea shares with much of Australia (National Geographic Society 1999; Stattersfield et al. 1998). Although the island of New Guinea is an 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 relative stability. The surface geology of the ecoregion consists of alluvium on active and relict alluvial plains and fans (Bleeker 1983).

This ecoregion is composed primarily of grasslands, although almost a third of the region is savanna, and there are areas of dry evergreen forest (Paijmans 1975; MacKinnon 1997). The pronounced seasonal rainfall, local relief, drainage, and the frequency of burning contribute to the variation in floristic structure (Miller et al. 1994). The savannas have strong structural and floristic affinities with those of northern Australia (Gillison 1983, in Miller et al. 1994). The dominant trees in the savannas include Eucalyptus, Albizia, and Melaleuca (Miller et al. 1994). The Melaleuca forest dominates areas that are submerged in up to 1 m of water during the wet season (R. Johns, pers. comm., 2000). An extensive belt of bamboo dominated by Schizistachyum occurs along the transitional stage between the adjoining forests and the savanna vegetation of the monsoonal area (Petocz 1989). The dune and beach communities in this ecoregion contain the uncommon Barringtonia asiatica (R. Johns, pers. comm., 2000).

Biodiversity Features
The overall richness and endemism of this ecoregion are low to moderate when compared with those of other ecoregions in Indo-Malaysia. There are forty-four mammal species in the ecoregion, including five species that are endemic or near endemic (Flannery 1995; Flannery and Groves 1998; Bonaccorso et al., in press) (table 1). Three of these species, the Papuan planigale (Planigale novaeguineae), the bronze quoll (Dasyurus spartacus), and the dusky pademelon (Thylogale brunii) are considered vulnerable (IUCN 2000).

Table 1. Endemic and Near-Endemic Mammal Species.

Family Species
Dasyuridae Planigale novaeguineae
Dasyuridae Dasyurus spartacus*
Dasyuridae Sminthopsis archeri*
Macropodidae Dorcopsis luctuosa
Macropodidae Thylogale brunii

An asterisk signifies that the species' range is limited to this ecoregion.

The ecoregion represents a portion of the Trans Fly EBA, which contains six restricted-range bird species. Five bird species are endemic or near endemic, including the vulnerable Fly River grassbird (Megalurus albolimbatus) (Stattersfield et al. 1998; Beehler et al. 1986; Coates 1985; IUCN 2000) (table 2). Tonda Wildlife Management Area is a globally significant wintering ground for migratory waders and waterfowl from Australia and the Palearctic (Beehler 1994).

Table 2. Endemic and Near-Endemic Bird Species.

Family Common Name Species
Alcedinidae Spangled kookaburra Dacelo tyro
Alcedinidae Little paradise-kingfisher Tanysiptera hydrocharis
Sylviidae Fly River grassbird Megalurus albolimbatus
Estrildidae Grey-crowned munia Lonchura nevermanni
Estrildidae Black munia Lonchura stygia

An asterisk signifies that the species' range is limited to this ecoregion.

This ecoregion forms the heart of the Southern Fly Platform Centre of Plant Diversity. Its flora is closely related to that of Australia (Davis et al. 1995).

The Trans Fly region is also critical habitat for several species of endemic amphibians and reptiles and is the only location of the pitted turtle (Carettochelys insculpta), a unique species in its own family (Allison 1994).

The key ecological process in savannas is fire. Although fires can occur during any rainless period, most savannas burn at the end of the dry season, when conditions are most favorable (Archibold 1995).

Current Status
Although the region is inhabited by a large number of sparsely distributed tribal groups, population pressure is low. Access from the outside of the ecoregion is poor, and there is generally little disturbance (Stattersfield et al. 1998; Davis et al. 1995). More than 90 percent of the original habitat is still intact in this ecoregion. The five protected areas, well-distributed between Indonesia and PNG, cover 9,530 km2, representing about 36 percent of the ecoregion area (table 3). Tonda, in PNG, and Wasur, in Indonesia, form a transboundary protected area complex that covers most of the coastal habitat (MacKinnon 1997).

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

Protected Area Area (km2) IUCN Category
Wasur 2,430 II
Wasur (extension) 1,020 PRO
Wasur (extension) 690 PRO
Rawa Biru 100 DE
Tonda 5,290 VIII
Total 9,530  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

Types and Severity of Threats
There is some threat on the Indonesian side from transmigration settlements, which result in increased hunting, wildlife trade, agricultural conversion, and unsustainable forestry practices. This would only be exacerbated by new roads, such as the planned Trans-Irian Highway (Stattersfield et al. 1998).

The introduction of rusa deer (Cervus timorensis) from other areas of Indonesia has had serious impacts on the grasslands of this ecoregion (Allison 1994).

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 savanna and grasslands in the Trans Fly region were placed in the Trans Fly Savanna and Grasslands [AA0708] under the Grasslands, Savannas, and Shrublands biome. This ecoregion also extends across the Arafura Sea to Australia, which was outside the region of analysis. 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
Reviewed by:
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.