Location and General Description
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 3000 km east of Australia at 16-20 o S latitude and 178 E-178 o W longitude. The islands of Viti Levu and Vanua Levu occupy 78 % of the land area in Fiji and support the tallest mountain at 1323 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 (Mueller-Dombois and Fosberg 1998). The oldest terrestrial areas have probably been exposed for 5-20 million years but the youngest island, Taveuni, last erupted 2000 years ago (Doyle and Fuller 1998). 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 (Ash 1992). 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 22o C in July to 28 o C in January (Ash 1992). Rainfall varies from 1500-2250 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 (Mueller-Dombois and Fosberg 1998). 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 (Smith 1979). 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 (Mueller-Dombois and Fosberg 1998). 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 (Mueller-Dombois and Fosberg 1998). Intermediate seasonal forests occurred between the dry and moist forest ecoregions (WWF & IUCN 1995).
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") (WWF & IUCN 1995). 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 (Mueller-Dombois and Fosberg 1998). 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 (Mueller-Dombois and Fosberg 1998). 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 (Mueller-Dombois and Fosberg 1998).
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 (Dahl 1980, Mueller-Dombois and Fosberg 1998). 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 (Dahl 1980). 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 (Pernetta and Watling 1978).
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; Gibbons 1981, Clunie 1985, Ryan 2000).
Archeological evidence indicates that burning of dry forest and subsequent erosion has been occurring in Fiji for up to 2500 years (Gibbons 1985). 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 (Ash 1992). 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, 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 (Dahl 1980).
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 (Gibbons 1981). 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; Clunie 1985).
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 (Mueller-Dombois & Fosberg 1998). 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 (1969) for Viti Levu and the monsoon forest lines of Collins et al. (1991) for Vanua Levu.
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Prepared by: Sandra Zicus, Tim Male
Reviewed by: In process