[1] The surface geology of Biak and Supiori consists mainly of rugged coralline limestone, with outcrops of schist overlain by basaltic lavas and tuffs.

Their physical isolation from New Guinea meant that plants and animals had to cross the ocean to get to the islands, giving rise to a unique flora and fauna that includes several endemic species.

The forests have a shrub and herb layer in the understory with a variety of palms, climbers, epiphytes, and ferns.

[1] Dominant emergent trees on the islands include Pometia pinnata and species of Ficus, Alstonia, and Terminalia.

Canopy trees include species of Garcinia, Diospyros, Myristica, Maniltoa, and Microcos.

[1] The recently discovered endemic palm Manjekia maturbongsii is found in lowland forests, between 80 and 170 meters elevation, on thin soils over limestone.

Five species are endemic to the ecoregion – the Biak glider (Petaurus biacensis), Blue-eyed spotted cuscus (Spilocuscus wilsoni), Biak naked-backed fruit bat (Dobsonia emersa), Biak giant rat (Uromys boeadii), and Emma's giant rat (Uromys emmae).

Biak and Supiori are home to endemic subspecies of the common spiny bandicoot, Echymipera kalubu philipi.

About half of the tree cover lost (572 ha) was primary forest.