[1] The islands on the eastern side of the chain are mostly made up of uplifted coraline rocks lying atop blocks of oceanic or continental crust.

Several of the islands on the western side of the chain are stratovolcanoes, including 'Ata, Tofua, Kao, Late, and Fonualei in the south, and Niuafo'ou, Niuatoputapu, and Tafahi in the north.

Common canopy trees include Diospyros spp., Rhus taitensis, Alphitonia zizyphoides, Calophyllum neo-ebudicum, Cryptocarya turbinata, Elattostachys apetala, Litsea mellifera, Maniltoa grandiflora, Myristica hypargyraea, Zanthoxylum pinnatum, Garcinia myrtifolia, Neonauclea forsteri, Didymocheton tongensis (on 'Eua), Podocarpus pallidus, Inocarpus fagifer, Erythrina fusca, Pisonia grandis, Pittosporum arborescens, Garuga floribunda, Ficus obliqua, Pleiogynium timoriense, and Cynometra grandiflora.

[1][4] The understorey includes dense clumps of the fern Dicranopteris linearis and the shrubs Piper puberulum and Psychotria insularum.

[1] On coastal dunes and relatively recent lava and ash deposits where soils are thinner and drier, forests of Casuarina equisetifolia predominate, with low trees and shrubs including Pandanus tectorius, Syzygium dealbatum, Hibiscus tiliaceus, and Scaevola taccada.

[1] Littoral forests of Hernandia nymphaeifolia, Barringtonia asiatica, and Casuarina equisetifolia grow closest to the coast in areas with salt spray.

Characteristic montane forest tree species include Syzygium spp., Fagraea berteroana, Bischofia javanica, Hernandia moerenhoutiana, Astronidium spp., and Reynoldsia spp.

Other native birds include the red shining parrot (Prosopeia tabuensis) and blue-crowned lorikeet (Vini australis).

[1] The islands are home to numerous seabirds, including brown noddy (Anous stolidus), Phoenix petrel (Pterodroma alba), and bristle-thighed curlew (Numenius tahitiensis).

Seabird breeding colonies are mostly limited to offshore islets free of rats, which prey on eggs and chicks.