The ecoregion includes the Tonga archipelago, a group of 170 islands that extends 800 km north to south between 15º to 23ºS latitude and 173º to 177º W longitude, and comprise the nation of Tonga. It also includes Niue, which lies 400 km east of Tonga at 19º S latitude and 169º W longitude.[1]
The Tonga archipelago lies at the boundary of the Pacific and the Australiantectonic plates, and the islands were created by the subduction of the Pacific Plate under the Australian Plate.[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. Some of the larger eastern islands are Foa, Lifuka, Vavaʻu, 'Eua, and Tongatapu. Several of the islands on the western side of the chain are of stratovolcanos, including 'Ata, Tofua, Kao, Late, and Fonualei in the south, and Niuafo'ou, Niuatoputapu, and Tafahi in the north.[3] The highest peak in the islands is 1,030 metres on Kao. Many islands have fringing coral reefs, and others have become coral atolls as the central islands eroded away or subsided.[1]
Niue is an uplifted coral atoll, with cliffs along the shoreline and without a fringing coral reef. It covers an area of 259 km2.[1]
The islands have been inhabited for about 3000 years.
Climate
The ecoregion has a humid tropical climate. Mean daily temperatures generally range from 24º to 30 °C in February, the warmest month, to 20º to 26 °C in August, the coolest month. Average annual rainfall is 2000 mm or more, and higher on windward slopes and at higher elevations. Rainfall is generally higher between December and April. Leeward lowlands can experience seasonal droughts between May and November.[1]
Mangrove scrub and mangrove forest are found in saltwater wetlands on coral atolls and around the shores of the larger islands' coastal lagoons.[1] Mangrove scrub is found on estuaries and reef flats and on the edges of mangrove forests. The small- to medium-sized trees Rhizophora mangle, Rhizophora stylosa, and Lumnitzera littorea are dominant. Where conditions are favorable mangrove forests dominated by Bruguiera gymnorhiza with Xylocarpus moluccensis and X. granatum replace the mangrove scrub.[3]
There are no native land mammals in the ecoregion. Native bats include the Pacific flying fox (Pteropus tonganus) and Pacific sheath-tailed bat (Emballonura semicaudata). The black rat (Rattus rattus) and brown rat (R. norvegicus) were introduced to the islands by humans, and have decimated the island's birds.[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.[1]
Niue has 12 native species of land birds and six species of seabirds, including two endemic subspecies.[1]
There are 20 known species of reptiles in the ecoregion. They include the Lau banded iguana (Brachylophus fasciatus), the boa Candoia bibroni, nine species of gecko, and nine species of skink. The skink Tachygia microlepsis is now considered extinct. Fossil remains of an giant land iguana have been found, which became extinct after the first humans arrived.[1]
Protected areas
A 2017 assessment found that 117 km2, or 21%, of the ecoregion is in protected areas.[2]
^ abcWhistler, W. Arthur (1992). "Vegetation of Samoa and Tonga". Pacific Science (1992), vol. 46, no. 2: 159-178
^ abFranklin, J., Wiser, S. K., Drake, D. R., Burrows, L. E., & Sykes, W. R. (2006). Environment, Disturbance History and Rain Forest Composition across the Islands of Tonga, Western Polynesia. Journal of Vegetation Science, 17(2), 233–244. http://www.jstor.org/stable/4499169
