[2][3][4] The ecoregion includes the foothills and lowlands south of New Guinea's Central Range.

The Southern New Guinea freshwater swamp forests ecoregion covers extensive areas of the Fly River lowlands to the south, and the lower reaches of some other rivers that drain from the highlands to the sea.

The Trans-Fly savanna and grasslands cover the southern tip of New Guinea.

The slopes of the Central Range above 100 meters elevation include some of the rainiest portions of New Guinea.

[7] The ecoregion has 69 species of mammals, principally marsupials, bats, and murid rodents.