The Carolines tropical moist forests is a tropical and subtropical moist broadleaf forests ecoregion in Micronesia. It includes the central and eastern Caroline Islands in the Federated States of Micronesia.
Geography
The ecoregion spans the central and eastern Caroline Islands, and include most of the Federated States of Micronesia it includes the states of Chuuk, Pohnpei, and Kosrae and the eastern islands of Yap State, known as the Remetau.
The ecoregion includes both high volcanic islands and low atolls, islands of coralline sand ringing a central lagoon.
The Chuuk islands are surrounded by almost circular barrier reef more than 60 km across at its widest point, which encloses a lagoon and 69 low islets composed of coral sand. Within the lagoon are 10 principal and many smaller volcanic islands in two clusters, the Faichuk group to the west and the Nomoneas group to the east. The largest island, Tol, reaches 443 meters elevation.
Pohnpei is an extinct volcano 650 km east of Chuuk. The island has an area of 335 km2. It is composed of weathered basalt, and geologically younger than Chuuk. The center of the island is a tableland with 11 separate peaks, the tallest of which reaches 734 meters elevation.
Kosrae lies 550 km to southeast of Pohnpei towards the eastern end of the Carolines. It is a deeply dissected volcanic island with several steep high peaks, the highest of which reaches 629 meters elevation.
The ecoregion includes many atolls and atoll groups, including the Hall Islands north of Chuuk, the Remetau group west of Chuuk, and the Nomoi Islands southeast of Chuuk, and the Senyavin Islands around Pohnpei.
Palikir, the capital of the Federated States of Micronesia, is on Pohnpei. The largest city is Weno in Chuuk.
Climate
The climate of the ecoregion is humid and tropical, with little variation in temperature from season to season. Rainfall is highest at the eastern end of the ecoregion, decreasing and becoming more seasonal towards the west. Pohnpei averages more than 4,500 mm of annual rainfall. Parts Kosrae receive more than 6,400 mm per year.
Flora
The natural vegetation of the islands was mostly tropical rain forest, with smaller areas of savanna and scrub, and mangroves along the shore. Atoll forests and coastal strand vegetation are found on the atolls. The principal forest types on the volcanic islands include lowland forest, montane forest, and cloud forest. Cloud forests occur as low as 450 meters on Pohnpei and 300 meters on Kosrae, which makes them some of the lowest-elevation tropical cloud forests in the world. The cloud forests are some of Oceania's most species-rich and are high in endemism. The islands are sufficiently close to Southeast Asia's diverse forests to allow plants to disperse, while the islands' age and relative isolation allowed plants to evolve into distinct species.
Humans have altered the islands vegetation, increasing the savanna area, especially in the western islands, with fires, and converting much of the lowland into gardens, fields, and plantations or secondary forest.
Pohnpei
Pohnpei is the highest and wettest island, and its vegetation is less degraded than the other islands.
The native lowland forests are mostly gone. There are areas of secondary forest and savanna, and well-preserved mangrove forests and freshwater swamp forests along the coast. Steeper slopes are covered in thickets of Hibiscus tiliaceus. About a third of Pohnpei is covered with a local silvicultural system of rotating tree gardens.
Areas of primary montane rain forest and cloud forest still exist in the mountainous center of the island. Upland forests are of two main plant associations, a Maesa carolinensis association between 450 and 680 meters elevation, and a Sphaeropteris lunulata–Pandanus patina on the highest slopes.
In the Maesa carolinensis association, the endemic palm Clinostigma ponapense forms the upper canopy layer, and the tree fern Sphaeropteris nigricans is dominant in the lower canopy. Maesa carolinensis and other shrubs are abundant in the understory. Other montane forest trees include species of Glochidion, Myrsine, Elaeocarpus, Syzygium, Psychotria, Timonius, Gynotroches, and Astronidium, and the palms Ptychosperma and Metroxylon. Lianas of Ipomoea, Merremia, Freycinetia, Hypserpa, and Pachygone are abundant, and there are many terrestrial and epiphytic ferns.