Hawaiian Rain Forest
These forests occur in the high rainfall areas of most of the main islands reaching elevations in excess of 1600 m. Like the dry forests, they are often dominated by the ubiquitous endemic Metrosideros polymorpha (Myrtaceae) and can have canopy heights up to 20 m. The great variation seen in Metrosideros polymorpha with foliage colour varying from dark, greenish, grey to bright green and flowers that vary in colour from crimson to light coral red have led to the recognition of a number of varieties. Other characteristic trees include a variety of endemics such as Antidesma platyphyllum (Euphorbiaceae), Bobea timonioides, Hedyotis terminalis, Psychotria hawaiiensis (Rubiaceae), Pisonia sandwicensis (Nyctaginaceae) and Tetraplasandra hawaiensis (Araliaceae). In the relatively undisturbed stands most of the under storey species are also endemic. Typical endemic shrubs include Cyrtandra platyphylla (Gesneraceae), Dubautia scabra (Asteraceae), Hedyotis hillebrandii (Rubiaceae), Lysimachia hillebrandii (Primulaceae), Myrsine sandwicensis (Myrsinaceae) and Vaccinium dentatum (Ericaceae). These forests are also rich in tree ferns with species such as the endemic Cibotium hawaiiense (Dicksoniaceae) together with tall growing ferns of the endemic genus Sadleria such as S. cyatheoides and S. pallida (Blechnaceae). The many smaller endemic ferns include Athyrium microphyllum (Athyriaceae) and Ctenitis rubiginosa (Dryopteridaceae). Among the vines, several endemic species of the Lamiaceae are relatively common including Phyllostegia vestita and Stenogyne rugosa, as is the endemic epiphytic shrub Clermontia clermontioides (Campanulaceae), while the rich epiphytic herbaceous flora includes the endemic Astelia menziesiana (Liliaceae) and a multitude of filmy ferns.
Hawaiian Lowland Dry ‘Metrosideros’ Forest
Lowland dry forest in which the endemic Metrosideros polymorpha (Myrtaceae) is usually present, but only predominating on Hawai’i, occurs on all of the main islands up to an altitude of about 1500 m. However, they tend to be confined to the dryer rain shadow areas. The canopy height varies from 4 to 20 m, and apart from the summer deciduous endemic species Erythrina sandwichensis (Fabaceae), Euphorbia haeleeleana (Euphorbiaceae) and Reynoldsia sandwicensis (Araliaceae) all of the woody plants are evergreen. The diversity of these forests seem to be correlated with island age with the best examples on the geologically older Kaua’I and O’ahu, while the examples on Hawai’i are relatively impoverished. Other important canopy trees include the endemic Colubrina oppositifolia (Rhamnaceae), Diospyros sandwicensis (Ebenaceae) and Nestegis sandwicensis (Oleaceae), any one of which may dominate depending on the area. Today only a few relict stands remain of this once extensive forest system, and in these can be found many other of the BioProvinces remaining endemic trees such as Alphitonia ponderosa (Rhamnaceae), Antidesma pulvinatum (Euphorbiaceae), Bobea sandwicensis (Rubiaceae), Charpentiera obovata (Amaranthaceae), Gardenia brighamii (Rubiaceae), Kokia drynarioides (Malvaceae), Myrsine lanaiensis (Myrsinaceae), Nothocestrum brevifolium (Solanaceae), Pittosporum hosmeri (Pittosporaceae), Pleomele aurea (Agavaceae), Pouteria sandwicensis (Sapindaceae), Rauvalvia sandwicense (Apocynaceae), Santalum ellipticum (Santalaceae), Sapindus oahuensis (Sapindaceae), Xylosma hawaiiense (Flacourtiaceae) and Zanthoxylum dipetalum (Rutaceae). In some cases these forests are somewhat open with a grassy ground layer, but where there is a closed canopy a diverse assemblage of under storey species can be found including many endemic shrubs like Delissea rhytidosperma (Campanulaceae) and Gossypium tomentosum (Malvaceae). Epiphytes, on the other hand, are scare, but there are a few endemic lianas such as Alyxia oliviformis (Apocynaceae) and Bonamia menziesii (Convolvulaceae).
Hawaiian Lowland Dry Shrublands
Natural shrublands occur in the leeward areas on all the main islands except Ni’ihau and Kaho’olawe up to an elevation of about 600 m, but tend to be confined to the more rugged, rocky areas. Composition of the dominant shrubs varies from place to place, but may include Dodonaea viscosa, or one of several endemic Wikstroemia species like W. monticola, W. oahuensis, W. phillyreifolia or W. sandwichensis (Thymelaeaceae), or various endemic Bidens species such as B. menziesii subsp menziesii (Asteraceae), or more rarely the endemic Sesbania tomentosa (Fabaceae). Other associated endemic species include shrubs or small trees such as Artemisia australis, Dubautia linearis, Wilkesia gymnoxiphium (Asteraceae), Chamaesyce celastroides (Euphorbiaceae), Santalum ellipticum (Santalaceae) and Sophora chrysophylla (Fabaceae). In the ground flora various grasses such as the endemic Eragrostis variablis (Poaceae) and various endemic herbaceous species like Argemone glauca (Papaveraceae) and Lipochaeta rockii (Asteraceae) may be present, while the few climbers or vines include the endemic Sicyos pachycarpus (Cucurbitaceae).
Hawaiian Acacia koa Forest
Forests dominated by the endemic Acacia koa (Fabaceae) extend from an altitude of about 300 m in the warm lowlands to about 2,300 m where cool sub alpine conditions prevail. They tend to be confined to leeward and windward slopes where conditions are slightly dryer. Acacia koa belongs to a largely Australian group of acacias whose functional leaves are actually flattened leaf stems or phyllodes. Young trees have the typical feathery leaves of acacias but these drop off and are replaced by phyllodes as the tree grows. Of considerable phytogeographical interest is the fact that the closest living relative of Acacia koa is A. heterophylla found on Reunion Island in the Indian Ocean. Other trees commonly associated with Acacia koa include a considerable number of endemic species such as Bobea elatior, Psychotria mariniana (Rubiaceae), Diospyros hillebrandii (Ebenaceae), Elaeocarpus bifidus (Elaeocarpaceae), Gardenia remyi (Rubiaceae), Myrsine kauaiensis (Myrsinaceae), Psydrax odoratum (Rubiaceae), Santalum freycinetianum (Santalaceae) and Syzygium sandwicensis (Myrtaceae). The shrub layer comprises species such as the endemic Boehmeria grandis, Pipturus albidus (Urticaceae), Broussaisia arguta (Hydrangeaceae), Cyanea angustifolia, Rollandia lanceolata (Campanulaceae), Phyllanthes distichus (Euphorbiaceae), Scaevola gaudichaudiana (Goodeniaceae) and Wikstroemia oahuensis (Thymelaeaceae). The ground vegetation, on the other hand, is usually fairly sparse with virtually no bryophytes. The few vascular plants include Oplismenus hirtellus, Paspalm orbiculare and the endemic Carex wahuensis (Cyperaceae). There also seem to be few epiphytic or climbing species, but these may include, for example, the primitive Psilotum nudum, the endemic climber Canavalia galeata (Fabaceae) and the endemic, epiphytic shrub Clermontia kakeana (Campanulaceae).
Hawaiian Montane Cloud Forest
Shrouded in fog on a regular basis, these forests form a belt stretching from an altitude of about 1000 m to the upper cloud limit set by the trade wind inversion at about 1900 m, and are typically composed of gnarled and stunted trees enveloped in mosses and lichens. They are characterized by the presence of lots of shade-adapted plants (sciophytes), and in this BioProvince by the lack of the heliophytic fern Dicranopteris linearis. Like so many of the Hawaiian forests the endemic Metrosideros polymorpha (Myrtaceae) is one of the major canopy trees, while other important trees include the endemic Acacia koa (Fabaceae), Cheirodendron faurii, C. trigynum (Araliaceae), Hedyotis terminalis (Rubiaceae) and Myrsine lesstiana (Myrsinaceae), but the actual composition varies for island to island. There is also good representation of endemic species of Coprosma (Rubiaceae) and Pelea (Rutaceae) including C. elliptica, C. kauensis, C. ochracea, C. pubens, C. rhynchocarpa, C. waimeae, P. christophersenii, P. clusiifolia, P. cruciata, P. feddei, P. haleakalae, P. oahuensis, P. orbicularis and P. volcanica, but again the composition varies from island to island. Tree ferns are also conspicuous with species like Cibotium glaucum and C. chamissoi, while other interesting elements include the endemic palm-like trees Cyanea tritomanth (Campanulaceae) and the endemic giant dock Rumex giganteus (Polygonaceae). The shrub layer is also very rich in species with about three times as many as in the dry forests. These include endemics like Cyrtandra paludosa (Gesneraceae), Touchardia latifolia, Urera glabra (Urticaceae) and Vaccinium calycinum (Ericaceae). The ground cover is composed largely of native ferns such as Dryopteris wallichiana, while the scattering of flowering plants includes endemics like Carex alligata (Cyperaceae), Luzula hawaiiense (Juncaceae) and Phyllostegia macrophylla (Lamiaceae). Vines and climbers include the endemic Stenogyne calaminthoides (Lamiaceae) and Vicia menziesii (Fabaceae), and there are several endemic lianas like Embelia pacifica (Myrsinaceae), Labordia hedyosmifolia (Loganiaceae) and Smilax melastomifolia (Smilacaceae).
Hawaiian Montane Bogs
The montane bogs of this BioProvince occur largely in clusters on the high plateaus, such as Alaka’I Swamp on Kaua’i or on flat-topped ridges as on the summit areas of Maui. Many occur on impervious ground but in the extreme high rainfall areas such as on the summit area of Mt Wai’ale’ale where rainfall exceeds 12 m per year this is not necessary. The vegetation is mostly composed of a hummocky matrix of sedges, mostly Rhynchospora lavarum and the endemic Oreobolus furcatus (Cyperaceae), and Sphagnum moss, but may include other endemic sedges such as Carex montis-eeka (Cyperaceae) and various grasses. Many of these bogs are important for local endemics. For example, the Silversward Bog of Mauna Loa includes the endemic silversward Argyroxiphium kauense (Asteraceae), while bogs on Maui include the closely related endemic ‘greensward’ Argyroxiphium grayanum. These are absent from the bogs on Kaua’I but here can be found the candelabra-like endemic Lobelia kauensis (Campanulaceae), while the endemic Lobelia grayana grows on the margins of certain Haleakala bogs. Other bog-based endemics include the peculiar Plantago krajinai (Plantaginaceae) with its large, white, wooly, deeply veined leaves.
Hawaiian Sophora-Myoporum Savanna (Parkland)
These open savanna-like communities dominated by Myoporum sandwicensis and the endemic Sophora chrysophylla (Fabaceae) are principally found on Hawai’i but there are some on East Maui. They occur as an interrupted belt above the montane forests on the high lava and ash slopes. On Hawai’i they are found primarily on Mauna Kea and to a lesser extent on Mauna Loa and Hualalai. Associated trees include the endemic Chamaesyce olowaluana (Euphorbiaceae) and Santalum haleakalae (Santalaceae), although many of the trees are very shrubby. A large proportion of the associated shrub and ground layer species tend to be concentrated under trees particularly Sophora trees where they benefit from ‘fog drip’. These include endemic shrubs like Chenopodium oahuense (Chenopodiaceae), Geranium arboreum (Geraniaceae), endemic herbs like Hesperocnide sandwicensis (Urticaceae), Sanicula sandwicensis (Apiaceae), and suspended from the trees and shrubs can be found the endemic vine Stenogyne microphylla (Lamiaceae).
Hawaiian Styphelia Heath Scrub
Above the Metrosideros tree line at about 2200 m the conditions become dryer due to the fact that the wet trade winds fail to rise over the mountains but deflected around the sides. The forests on Hawai’i and Maui therefore give way to savanna or parklands and pastures but above or intermingled with these are heathland scrub dominated by microphyllous or sclerophyllous species. The main shrub is Styphelia tameiameiae, but depending on location this may be accommpanied by various endemic species such as Coprosma montana (Rubiaceae), Dubautia ciliolata (Asteraceae), Geranium cuneatum (Geraniaceae) or Vaccinium reticulatum (Ericaceae). Between the scrubs the bracken Pteridium aqulinium var. decompositum can be common, together with several endemic grasses including Deschampsia nubigena, Panicum tenuifolium and Trisetum glomeratum (Poaceae).
Hawaiian Alpine Dry ‘Argyroxiphium’ Shrublands
This type vegetation is confined to East Maui and Hawai’i at altitudes ranging from about 3000 and 3400 m. In addition to low levels of precipitation, this zone is also marked by frequent frosts, which can also occur in summer. An interesting characteristic of the vegetation is that a comparatively large proportion is composed of plants with affinities to American species, rather than Indomalesian like most of the lowland flora. These include several endemic members of the Asteraceae such as Argyoxiphium sandwicense, Dubautia arborea, D. menziesii and Tetramalopium humile, and the endemic Silene struthioloides (Caryophyllaceae), all of which are shrubs. However, being predominantly found on barren gravels, debris and cinders, this community has a very open appearance, and from a distance these areas look almost devoid of plant life.
Hawaiian Coastal Vegetation
Many of the steep cliffs of this BioProvince are almost devoid of plants except for those found in crevices such as tufted species like Fimbristylis cymosa and the endemic Hedyotis littoralis (Rubiaceae), together with the strange endemic, Brighamia insignis (Campanulaceae) with its unbranched, succulent stems. On the coastal slopes of tuff or disintegrating lava Baerhavia acutifolia, Sida fallax and the endemic Jacquemontia ovalifolia (Convolvulaceae) are common, while other species like the rare endemic Schiedea globosa (Caryophyllaceae) is confined to O’ahu. On limestone shores (elevated coral reefs) the plant assemblage is very different and typically includes Lycium sandwichensis, Portulaca lutea, Sesuvium portulcastrum and the two endemic shrubs Chenopodium oahuensis (Chenopodiaceae) and Capparis sandwichiana (Capparaceae) – the latter producing beautiful nocturnal flowers. Moving on to the sandy shores the cosmopolitan Ipomoea pes-caprae occurs together with Boerhavia repens, Reichardia picroides, Vigna marina and several other hardy plants. However, the adjacent sand dunes provide habitat for a richer assembage of species. Here can be found several species able to bind or stabilize sand including Heliotropium anomalum, Vitex ovata, Scaevola taccada, Sporobolus virginicus and the endemic Nama sandwicensis (Hydrophyllaceae) and Sesbania tomentosa (Fabaceae). Much of the sand is composed of coral fragments, but on Hawai’i there is also black, volcanic sand, which has a very poor flora mainly comprising Ipomoea pes-caprae. Finally, it may be surprising to hear that mangroves were absent from the Hawaiian Islands prior to the introduction of several species of Rhizophoraceae at the beginning of the last century. Since then they have rapidly spread throughout the islands.
Hawaiian Coastal Grasslands
Natural coastal grassland dominated by the endemic Eragrostis variabilis (Poaceae) occurs on all of the main islands, but only forms the dominant grassland association on the northwestern islands. Other associated endemic plants include various shrubs such as Achyranthes splendens (Amaranthaceae) and Solanum nelsonii (Solanaceae), and the climber Sicyos maximowiczii (Cucurbitaceae). The pan tropical Sporobolus virginicus grassland also occurs in pockets throughout the archipelago but extensive stands are now confined to a few undisturbed dune systems. Associated endemic species include the shrub Chamaesyce degeneri (Euphorbiaceae) and the herb Gnaphalium sandwicensium (Asteraceae).
Further information required.
References
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