Fiji tropical dry forests
Fiji. (Photograph by David Olson)
Introduction Tropical dry forests are limited to relatively large islands in the tropical South Pacific where mountains create rain shadows. The Fijian and New Caledonian dry forests are the largest dry forests of the region, both support a large number of endemic species and both are critically endangered with only remnants remaining. (Fiji tropical dry forests)
Location and General Description
WWF
Long, dry winters are typical in the northwest of Fiji’s large islands and have produced extensive dry forest communities unique in the Pacific. Unfortunately, this forest which once covered 7557 km2 is now found on less than 100 km2 and is probably one of the most endangered habitats in the tropical Pacific.
The more than 300 islands of Fiji are located 3,000 km east of Australia at 16-20° S latitude and 178 E-178° W longitude. The islands of Viti Levu and Vanua Levu occupy 78% of the land area in Fiji and support the tallest mountain at 1,323 meters (m). Most islands are the remnants of once active volcanoes on a piece of the Pacific Plate that is drifting slowly southeast through an extensive zone of fracturing, volcanism, and shearing resulting from the subduction of the Pacific Plate under the Australian Plate. The oldest terrestrial areas have probably been exposed for 5-20 million years but the youngest island, Taveuni, last erupted 2000 years ago. Most soils are derived from volcanic material, but some are comprised of uplifted marine reefs and sediments and rivers on older islands have formed alluvial plains of sedimentary soils. The orientation of Fiji’s mountains and the constancy of southeast trade winds results in a rain shadow to the northwest of high mountain areas. Tropical dry forest is found in these areas on the larger islands and on island groups in the lee of larger islands. The climate here is tropical with mean monthly temperatures ranging from 22 °C in July to 28 °C in January. Rainfall varies from 1500-2250 millimeters (mm) per year but is strongly seasonal with most falling during December-April summer and almost drought conditions prevailing during the cooler remainder of the year. Cyclones coming from the northwest hit the islands between November-April every few years.
Tropical dry forest once occupied about one third of the land area of Fiji’s largest high islands. The canopy of dry forest is dominated by two species, Dacrydium nidulum and Fagraea gracilepes. Other species present are Myristica castaneifolia, Dysoxylum richii, Parinari insularum, Intsia bijuga, Syzygium spp., Aleurites moluccana, Ficus theophrastoides, areas of bamboo (Bambusa spp.), and the gymnosperms Podocarpus neriifolius, a cycad (Cycas seemannii), and Gymnostoma vitiense. Even drier areas once supported a subtype of forest dominated by an endemic sandalwood (Santalum yasi), Casuarina equisetifolia, and Gymnostoma vitiense and climbing ferns (Lygodium scandens). The most disturbed dry forests occur as a lightly wooden savanna on eroded and degraded soils and are dominated by C. equisetifolia with an understory of Mussaenda raiateensis, Decaspermum fruticosum, Dodonaea viscosa, C. seemannii, and the palm Pritchardia pacifica. Intermediate seasonal forests occurred between the dry and moist forest ecoregions.
Many areas that were once covered by dry forest have been burned often enough that they now support open grassland and savanna called talasiqa (meaning "sun burnt"). The soils in these areas are so depleted by fire and erosion that only sparse vegetation survives. Sporobolus indicus is the most common grass with the ferns Pteridium aquilinum and Dicranopteris linearis also present; S. indicus grassland covers close to 25% of Viti Levu and Vanua Levu. An additional type of relatively dry forest is found in coastal strand vegetation in a narrow belt around all the islands. Most of the species in this community are present in coastal areas throughout the Pacific. Scaevola taccada, Wollastonia biflora, Sophora tomentosa, and Clerodendrum inerme dominate areas near the shore. Further inland, Barringtonia asiatica, Calophyllum inophyllum, Hibiscus tiliaceus, Cocos nucifera, Pandanus tectorius, and Casuarina equisetifolia dominate the forest.
Biodiversity Features
Remnant dry forest, near Koroiyaca, Viti Levu, Fiji. (Photograph by David Olson) It is difficult to know what plant and animal species were characteristic of dry forest because it has been rare since biologists began cataloging Fiji’s biodiversity. Sandalwood forest dominated by an endemic species would have covered extensive areas of dry land and probably supported a large fauna of pollinating and fruit-feeding invertebrates and birds. Today, the sandalwood, S. yasi, is an endangered species limited to a small relict population with recruitment prevented by fire. In drier areas on Vanua Levu, small patches of forests characterized by Casuarina equisetifolia, Gymnostoma vitienses, and the rare Santalum yasi (sandalwood) still remain.
No passerines are known to have been dry forest specialists but two non-passerines, the whistling tree duck (Dendrocygna arcuata) and grass owl (Tyto longimembris), both used dry habitats for foraging and are now most probably extinct. The bolo snake (Ogmodon vitianus) and Pacific boa (Engyrus bibronii and E. australis) are found in the transition forests between dry and wet areas and may have once been present in dry forests.
Coastal dry forests occur across many of the islets and atolls in Fiji where they support large numbers of breeding seabirds, Pacific pigeon (Ducula pacifica), purple-capped fruit-dove (Ptilinopus porphyraceus), collared lory (Phigys solitarius), crested iguana (Brachylophus spp.), and coconut crabs (Birgus latro).
Current Status
Archeological evidence indicates that burning of dry forest and subsequent erosion has been occurring in Fiji for up to 2500 years. Today, most areas have been converted to sugar cane, exotic tree plantation or grazing lands or have experienced such frequent burning and erosion since human settlement that sparse sedge-fern talasiqa grassland is all that the soil can support. Talisiqa covers more than 3,000 km2. It is debatable whether this habitat existed at all before human arrival. The soils in these areas are so impoverished that very little vegetation grows and tropical downpours and cyclone rains cause massive erosion further reducing the soil. At least 300 km2 have been planted with Pinus caribaea plantation in hopes they will stabilize soils and prevent erosion. These forests currently supply about 30 percent of Fiji’s timber. A few small patches of dry forest remain on Vanua Levu, Viti Levu, Yaduataba Island, and on small islands in the Mamanuca and Yasawa Groups. None of the remaining dry forest areas are protected in reserves and there is a danger that these areas will be completely destroyed, through fire or clearing (Deforestation), before any effort is made to survey or save them. Every effort should be made to survey remaining forests in these areas to identify the most diverse and extensive communities remaining and to start the process leading to their protection.
Types and Severity of Threats
Coastal forest is still fairly widespread, but is highly impacted on inhabited islands. In addition, the introduction of herds of goats to uninhabited islands has had a disastrous effect on coastal forests and seabird populations in low islands. Domestic grazers, including cattle and goats, are increasing on the islands, as are uncontrolled feral populations of goats and pigs. Introduced mongooses, cats, dogs, and rats, as well as humans, have had a severe impact on populations of ground-nesting birds and native lizards. The remote Ringgold Islands, a collection of sparsely inhabited islands to the far northeast of Fiji’s main islands support large numbers of breeding seabirds. In particular, Vetaua Island deserves protection as it supports a breeding colony of tens of thousands of Red-footed Booby (Sula sula), Brown Booby (Sula leucogaster), Common Noddy (Anous stolidus), and Black Noddy (Anous minutus).
Justification of Ecoregion Delineation
This ecoregion includes the seasonally dry zones of the main Fijian islands of Vanua Levu and Viti Levu, which are distinct from the low islands and the wetter zones on the high islands. The majority of the Fiji Islands (including Rotuma, Wallis and Futuna) are delineated as one ecoregion, the Fiji Wet Tropical Forests ecoregion. The boundaries of the Dry Forest are based on Cochrane for Viti Levu and the monsoon forest lines of Collins et al for Vanua Levu.
Additional information on this ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
Further Reading
- Ash, J. 1992. Vegetation ecology of Fiji: Past, present, and future perspectives. Pacific Science 46:111-127.
- Clunie, F. 1985. Seabird nesting colonies of the Ringgold Islands. Domodomo, 3:90-109.
- Cochrane, G.R. 1969. Problems of vegetation change in western Viti Levu, Fiji, in Gale, F., and G.H. Lawton. Settlement and Encounter: Geographical Studies presented to Sir Grenfell Price. Oxford University Press, Melbourne, Australia.
- Collins, N.M., J.A.Sayer, and T.C. Whitmore. 1991. The Conservation Atlas of Tropical Forests: Asia and the Pacific. Macmillan Press, London. ISBN: 013179227X
- Dahl, A.L. 1980. Regional ecosystems survey of the South Pacific area. South Pacific Commission, Noumea, New Caledonia.
- Dahl, A.L. 1986. Review of the protected areas system in Oceania. International Union for Conservation of Nature and Natural Resources, Commission on National Parks and Protected Areas, in collaboration with the United Nations Environment Programme. ISBN: 2880325099
- Doyle, M.F., and D. Fuller. 1998. Palms of Fiji-I. Endemic, indigenous, and naturalized species: changes in nomenclature, annotated checklist, and discussion. Harvard Papers in Botany, 3:95-100.
- Gibbons, J.R.H. 1981. The biogeography of Brachylophus (Iguanidae) including the description of a new species, B. vitiensis, from Fiji. Journal of Herpetology, 15:255-273.
- Gibbons, J.R.H. 1985. Brief environmental history of Fiji. Domodomo, 3:110-127.
- Keast, A. 1996. Pacific biogeography: Patterns and processes. Pages 495-497 in A. Keast and S.E. Miller, editors. The Origin and Evolution of Pacific Island Biotas, New Guinea to Eastern Polynesia: Patterns and Processes. SPB Academic Publishing bv. Amsterdam, The Netherlands. ISBN: 905103136X
- Mueller-Dombois, D. and F.R. Fosberg. 1998. Vegetation of the Tropical Pacific Islands. Springer Press, New York. ISBN: 038798285X
- Pernetta, J.C. and D. Watling. 1978. The introduced and native terrestrial vertebrates of Fiji. Pacific Science, 32:223-243.
- Ryan, P.A. 2000. Fiji's natural heritage. Exisle Publishing Limited, Auckland, New Zealand. ISBN: 0908988141
- Smith, A.C. 1979. Flora Vitiensis Nova. Volume 1. Pacific Tropical Botanic Garden, Lawai, Hawaii.
- Stattersfield, A.J., M.J. Crosby, A.J. Long, and D.C. Wege. 1998. Endemic bird areas of the world: priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International. Cambridge, UK. ISBN: 0946888337
- WWF and IUCN. 1995. Centres of plant diversity. A guide and strategy for their conservation. Vol. 2. Asia, Australasia and the Pacific. IUCN Publication Unit, Cambridge, UK. ISBN: 2831701988
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