The southern and northern islands are within the trade wind belt, and regularly receive 1,500 and 3,000 mm of annual rainfall.

The characteristic species are common to coastal Indo-Pacific areas, and include the trees Pisonia grandis, Calophyllum inophyllum, Heliotropium foertherianum, Pandanus tectorius, Cordia subcordata, and Guettarda speciosa, and the shrubs Morinda citrifolia, Scaevola taccada, Suriana maritima, and Pemphis acidula.

[1] The driest and lowest islands are covered with low plants, including the grass Lepturus repens and the creepers Tribulus cistoides or Portulaca lutea, with areas of Heliotropium foertherianum, Pemphis acidula, and Scaevola taccada scrub.

The sole passerine bird is the endemic bokikokiko (Acrocephalus aequinoctialis), a reed warbler found on Teraina, Tabuaeran, and Kiritimati.

Kuhl's lorikeet (Vini kuhlii) is an endangered parrot found on Kiritimati and Teraina and on Rimatara in the Tubuai Islands to the southeast.