Location and General Description
The 12 Marquesas Islands are located approximately 5,500 km west of South America at 8º to 11ºS latitude and 139º to 141ºW longitude. All islands in the group are volcanic high islands with the northwest islands being approximately 6 million years old, and the southeast are the youngest at 1.3 million years old (Florence & Lorence 1997). The topography is very steep with knife-edged ridges, deeply dissected gorges and cliffs extending from mountaintops straight to sea level. Southeast trade winds are fairly constant year-round and moderate the rainfall and temperature, but long droughts can occur during El Nino cycles (Florence & Lorence 1997). Variation in topography and orientation produces variation in annual rainfall throughout the islands, ranging from 500 mm on lowland leeward coasts to more than 4,000 mm above 1,000 m on the five highest islands. Eastern upland areas tend to be wettest and coolest with mean temperatures from 15° to 25oC while western lowlands are drier and hotter with temperatures averaging 25° to 29oC. (Adamson 1936).
Tropical moist forest are dominated by different species depending on elevation and rainfall (Florence & Lorence 1997). Lowland forest occurs up to about 300 m where annual precipitation is less than 2,000 mm. It is dominated by Pisonia grandis reaching 15 m, Thespesia populnea, Calophyllum inophyllum, and Terminalia glabrata. Tropical dry forest, with Hibiscus, Pandanus, Thespesia, and Cordia, once covered lower slopes on larger islands such as Eiao and Fau Huku (Dekker 1992, WWF & IUCN 1995). Mid-elevation forest with a canopy up to 20 m in height occurs between elevations of 300 to 800 m with annual rainfalls of 2,000 to 3,000 mm. Typical species include Hibiscus tiliaceus, Pandanus tectorius, Alphitonia marquesensis, Weinmannia parviflora, with an understory of Angiopteris evecta and Cyclophyllum barbatum (Florence & Lorence 1997, Mueller-Dombois & Fosberg 1998). At slightly higher elevations, forests are dominated by Hernandia nukuhivensis, Cyathea affinis and C. feanii in wet areas, and Metrosideros collina and W. parviflora on drier slopes. Above 1,000 m, cool and misty conditions surround stunted cloud forest dominated by Cheirodendron bastardianum, Ilex anomala, and M. collina , and Freycinetia spp. climbers (Florence & Lorence 1997). Areas above 1,200 m are drier, and this windswept community supports a heathland less than 1 m high dominated by M. collina, Vaccinium cereum, Styphelia tameiameiae, and Bidens spp. with grasses and ferns (Mueller-Dombois & Fosberg 1998).
The Marquesas are among the most isolated archipelagos in the world and thus have a highly endemic biota. The islands support 320 native vascular plant species with 42 percent endemism, including two endemic genera (WWF & IUCN 1995, Florence & Lorence 1997). There are approximately 200 introduced plant species. A number of genera including Asplenium, Psychotria, Bidens, Cyrtandra, Peperomia, Myrsine, Cyperus, and Melicope have numerous endemic species that evolved in the Marquesas from single ancestral species (Wagner 1991). The fern flora is particularly rich (WWF & IUCN 1995). Three plant species have become extinct and 16 species are endangered (Dahl 1980). The islands support a fairly rich invertebrate fauna with a notable diversity of at least 78 land and freshwater snail species and 16 fruit fly (Drosophila) species (Adamson 1935).
The Marquesas support 19 breeding seabird species and 11 resident land birds. The endangered ultramarine lory (Vini ultramarina) has declined from an archipelago-wide distribution prehistorically to only the island of Ua Huka recently (Steadman 1989, Kuehler et al. 1997, Stattersfield et al. 1998). Today, a translocation program has reestablished a population on Fatu Hiva which is free of alien black rats (Rattus rattus) thought to be a major factor in its decline elsewhere (Keuhler et al. 1997). The red-mustached fruit-dove (Ptilinopus mercierii) has become extinct and the Nuku Hiva pigeon (Ducula galeata) has a population of fewer than a few hundred birds on Nuku Hiva Island (Dahl 1980). Other threatened or endangered endemic bird species include the Marquesas ground-dove (Gallicolumba rubescens), Marquesas kingfisher (Halcyon godeffroyi), Fatuhiva monarch (Pomarea whitneyi), Iphis monarch (P. iphis), and Marquesas monarch (P. mendozae)(Dahl 1980).
Human habitation has influenced Marquesan ecosystems for millennia. Polynesians colonized the islands between 1,000 to 2,000 years ago. They reached a population peak of about 80,000 inhabitants several hundred years ago which was accompanied by the destruction of most lowland vegetation and in the formation of grassland in drier, frequently burned areas (Rolett 1993). The archaeological work in the Marquesas has revealed an extensive history of extinction and extirpation of birds (Steadman & Rolett 1996). Excavations on Ua Huka show that the island once supported 7 more seabird species than are present today and 13 land birds that are now gone, including 10 endemic rails, pigeons and parrots (Steadman 1995). Summary of all archaeological work indicates that 10 land birds became extinct and 7 bird species were extirpated from most of their range (Steadman & Rolett 1996). All remaining endemic birds are considered threatened, some critically (Stattersfield et al. 1998).
Designation of conservation areas in the Marquesas must be accompanied by major control efforts for alien species and fire, and habitat restoration efforts. Two reserves, Eiao Island and the dry forest reserve on Mohotani, have been so totally denuded by feral sheep and other animals that rainfall washes away so much soil that plants cannot regenerate (Montgomery et al. 1980). Introduced great horned owl and common myna are thought to greatly impact native bird species on Hiva Oa (Stattersfield et al. 1998). In addition to mammals, birds, and rats, the introduced plant Miconia magnifica is established and spreading. It has the potential to completely replace all native forest as its congener has done in parts of Tahiti (Montgomery et al. 1980). Hunting is a major factor in the endangerment of the Nuku Hiva or Marquesan imperial-pigeon, a species with less than 300 individuals left (Stattersfield et al. 1998).
The protection and management of upper-elevation forests on Ua Pou, Nuku Hiva, Fatu Hika, Ua Huku, and Fatu Hiva Islands would serve to protect large numbers of endemic plant species and the unique communities they form (Dahl 1980, Montgomery et al. 1980, Thibault 1988, Seitre & Seitre 1992, Florence & Lorence 1997).
Types and Severity of Threats
Lowland forests were completely replaced with introduced species (Florence & Lorence 1997). Following European contact, introduced diseases wiped out all but approximately 3,800 Polynesian inhabitants. The subsequent introduction of herbivorous and predatory mammals has had an even more catastrophic effect on upland flora and fauna (Rolett 1993). Frequent fires have also transformed many natural habitats and works to maintain introduced communities. Uninhabited islands, such as Hatutaa, that are protected from human habitation and mammals still support large numbers of seabirds and land birds, but few areas of natural forest are currently included in the reserve system (Dahl 1980).
Justification of Ecoregion Delineation
This ecoregion consists of the relatively discrete Marquesas Islands group. Allison treats the Cooks, Societies, Tuamotus, and Marquesas as a unit herpetologically as they share a similar reptile assemblage. Van Balgooy (1996) similarly lumps the Cooks, Niue, Societies, Tuamotus, Tubaui, and Marquesas based on floristic affinities. However, Birdlife International (Stattersfield et al. 1998) separates the Marquesas from surrounding island groups due to the presence of 10 endemic bird species, and based on this consideration we have delineated the Marquesas as a separate ecoregion.
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Prepared by: Tim Male
Reviewed by: In process