The Hawaiian tropical rainforests are a tropical moist broadleaf forest ecoregion in the Hawaiian Islands. They cover an area of in the windward lowlands and montane regions of the islands. Coastal mesic forests are found at elevations from sea level to . Mixed mesic forests occur at elevations of , while wet forests are found from . Moist bogs and shrublands exist on montane plateaus and depressions.
For the 28 million years of existence of the Hawaiian Islands, the tropical rainforests have been isolated from the rest of the world by vast stretches of the Pacific Ocean, and this isolation has resulted in the evolution of an incredible diversity of endemic species, including fungi, mosses, snails, birds, and other wildlife. In the lush, moist forests high in the mountains, trees are draped with vines, orchids, ferns, and mosses. This ecoregion includes one of the world's wettest places, the slopes of Mount Waialeale, which average of rainfall per year.
Coastal mesic forests are found on the windward slopes of the major islands from sea level to . These forests have been dominated by the native hala (Pandanus tectorius) and hau (Hibiscus tiliaceus) and naturalized (Polynesian introductions) kukui (Aleurites moluccana) and milo (Thespesia populnea) for the past 1,000âÂÂ2,000 years. The Polynesian-introduced noni (Morinda citrifolia), pia (Tacca leontopetaloides), and kë (Cordyline fruticosa) are also common in this zone. Other native species include pololei (Ophioglossum concinnum), ÃÂkia (Wikstroemia spp.), loulu fan palms (Pritchardia spp.), à Âhia lehua (Metrosideros polymorpha), and lama (Diospyros sandwicensis).
Mixed mesic forests, at on the windward slopes of the large islands in addition to the summit of Mount LÃÂnaihale on LÃÂnai, receive of rainfall annually and thus may not be true rainforests. The forest canopy, dominated by koa (Acacia koa) and à Âhia lehua (Metrosideros polymorpha), is somewhat open, but tree density is rather high. Other trees and shrubs include pÃÂpala (Charpentiera obovata), olopua (Nestegis sandwicensis), hame (Antidesma platyphyllum), mÃÂhame (A. pulvinatum), kà Âpiko (Psychotria mariniana), à Âpiko (P. mauiensis), iliahi (Santalum freycinetianum), hà Âlei (Ochrosia spp.), poolà(Claoxylon sandwicense), kà Âlea lau nui (Myrsine lessertiana), kauila (Alphitonia ponderosa), nioi (Eugenia reinwardtiana), aiai (Paratrophis pendulina), and hà Âawa (Pittosporum spp.).
Wet forests generally occur from , but may be as low as . They receive of rain per year. à Âhia lehua (Metrosideros polymorpha) is the dominant canopy species in wet forests, but koa (Acacia koa) is also very common. Other trees include kÃÂwau (Ilex anomala), alani (Melicope clusiifolia), à Âhia ha (Syzygium sandwicensis), kà Âlea lau nui (Myrsine lessertiana), ohe (Tetraplasandra spp.), and olomea (Perrottetia sandwicensis) as well as hÃÂpuu (Cibotium tree ferns). Apeape (Gunnera petaloidea), oha wai (Clermontia spp.), hÃÂhà(Cyanea spp.), kÃÂmakahala (Geniostoma hirtellum), kanawao (Broussaisia arguta), Phyllostegia spp., ÃÂkala (Rubus hawaiensis), kÃÂmanamana (Adenostemma lavenia), Pilea peploides, mÃÂmaki (Pipturus albidus), olonà(Touchardia latifolia), and alaala wai nui (Peperomia spp.) are common understory plants. Vines include maile (Alyxia oliviformis) and hoi kuahiwi (Smilax melastomifolia). Iei.e. (Freycinetia arborea), puaakuhinia (Astelia menziesiana) and à Âlapa (Cheirodendron trigynum) are epiphytic flowering plants found in wet forests. Epiphytic ferns, such as Adenophorus spp., ohiaku (Hymenophyllum recurvum), Ophioglossum pendulum, ÃÂkaha (Asplenium nidus), ÃÂkaha (Elaphoglossum hirtum), and makue lau lii (Grammitis hookeri), cover trees. Epyphytic mosses include Acroporium fuscoflavum, Rhizogonium spiniforme, and Macromitrium owahiense. Loulu fan palms (Pritchardia spp.) may tower over the forest canopy.
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Bogs are found in montane regions where rainfall exceeds drainage. Dominant vegetation in bogs are shrubs, sedges, and grasses. Larger shrubs and small trees grow on bog perimeters or on raised hummocks. Carex spp., Oreobolus furcatus, and Rhynchospora rugosa are common sedges, shrubs include à Âhelo kau laau (Vaccinium calycinum) and à Âhelo (V. dentatum), while grasses are represented by Dichanthelium spp. and Deschampsia nubigena. Dwarf varieties of à Âhia lehua (Metrosideros polymorpha vars. incana and glabriofolia) are the most seen trees on the edges of bogs. The ferns wÃÂwaeiole (Lycopodiella cernua), amau (Sadleria spp.), and uluhe (Dicranopteris linearis) grow in bogs. Rare plants include liliwai (Acaena exigua), naenae (Dubautia spp.), and Argyroxiphium spp.