The group has four central islands, Yap, Gagil-Tomil, and Maap, and Rumung, which are separated by narrow channels.

Humans have altered the islands' vegetation, and converted the lowland forests to farms, plantations, and tree gardens.

The canopy layer has a diverse mix of tree species including Celtis sp., Buchanania engleriana, Campnosperma brevipetiolata, Trichospermum ikutai, Garcinia rumiyo, Pentaphalangium volkensii, Terminalia catappa, Planchonella obovata, Pangium edule, Aidia cochinchinensis, and Eurya japonica.

The understory shrub layer includes species of Psychotria, Crateva, Streblus, Glochidion, Leea, Hibiscus, Polyscias, and Ixora.

The upland forest is denser and forms a closed canopy in better-watered areas and on deeper soils, and is much more open on exposed or rocky slopes.

These managed forests are composed of a mix of species, mostly introduced, which includes coconut palm (Cocos nucifera), breadfruit, betel nut, papaya, banana, cassava, two types of taro, and a variety of medicinal and ornamental plants.

The introduced Polynesian rat (Rattus exulans) and brown tree snake (Boiga irregularis) prey heavily on native birds.