Included here are the Caroline Islands, Mariana Islands, Marshall Islands, Gilbert Islands, Ellice Islands, Phoenix Islands, Tokelau Islands, Baker Island, Banaba Island, Howland Island, Nauru Island and Wake Island.

Micronesian Limestone Forest

Forest on limestone that has been significantly elevated above sea level is one of the most important vegetation types in Micronesia. Large stands occur on Guam and other islands in the southern Marianas, in the southern half of the Belau Islands and Fais in the Carolinas, and on Banaba and Nauru west of the Gilbert Islands. Their canopy heights vary considerable but can exceed 30 m and there is often a sub-canopy layer that may reach 15 m or more.  On Guam the characteristic trees are largely composed of endemic species such as Aglaia mariannensis (Meliaceae), Atrocarpus mariannensis (Moraceae), Bleekeria mariannensis (Apocynaceae), Elaeocarpus sphaericus (Elaeocarpaceae), Glochidion marianum, Macaranga thompsonii (Euphorbiaceae), Guamia marianum (Annonaceae), Jasminium marianum (Oleaceae), Pandanus fragrans (Pandanaceae) and Psychotria hombroniana (Rubiaceae). Epiphytes are well represented with many bryophytes, ferns and orchids, and the strangling habit is common among species of Ficus. These begin life epiphytically then send down aerial roots, which eventually become so numerous that they kill the host tree.  The undergrowth also includes a wide variety of species including endemic shrubs like Discocalyx megacarpa (Myrsinaceae), Eugenia palumbis (Myrtaceae), Maytenus thompsonii (Celastraceae) and Piper guahamense (Piperaceae).  In fact, something like 36% of species in these forests are endemic, and usually have a higher level of endemism than any other habitat. Although certain trees such as Atrocarpus mariannensis, Cordia subcordata, Ficus prolixa, Mammea odorata, Merrilliodendron megacarpa and Pandanus tectorius may form local dominants, in general species distribution is so equitable that they are hard to characterize by reference to dominant species.

References

Endress, B. A. 2002. The importance of endemic species to forest succession in Palau. Micromesica, 34: 141-153.

Fosberg, F. R. 1960. The vegetation of Micronesia. Bulletin of the American Museum of Natural History, 119: 1-75.

Fosberg, F. R., Sachet, M. H. & Oliver, R. 1979. A Geographical Checklist of the Micronesian Dicotyledonae. Micronesica, 15: 41-295.

Fosberg, F. R. 1984. Phytogeographic comparison of Polynesia and Micronesia. In: Biogeography of the Tropical Pacific (Proceedings of a Symposium). Eds. F. J. Radovsky, P. H. Raven and H. Sohmer. Bishop Museum Special Publication No. 72.

Morton, J. M., Amidon, F. A. & Quinata, L. R. 2000. Structure of a limestone forest on northern Guam. Micronescia, 32: 229-244.

Mueller-Dombois, D. & Fosberg, F. R. 1998. Vegetation of the Tropical Pacific Islands. Springer.

Schmid, M. 1989. The forests in the tropical Pacific archipelagoes. In: Ecosystems of the World 14B - Tropical Rain Forest Ecosystems.  Elsevier.

Stone, B. C. 1970-71. The Flora of Guam. Micronesica, 6: 1-659.