Vegetation Ecology of Fiji: Past, Present, and Future Perspectives

Abstract

The Fiji Archipelago comprises a Tertiary island arc with several hundred small and a few large mountainous islands near the northeastern corner of the Australian tectonic plate, 3000 km from continental Australia-New Guinea. Despite contrary prevailing winds and ocean currents, the flora is very largely derived from that of Malesia, and the largest component was probably dispersed by frugivorous birds or bats, of which several taxa are established in Fiji. About 25% of the native vascular plant species are endemic and, with exceptions such as the relictual Degeneria, most have apparently diverged from overseas conspecifics. There are a few cases where speciation has occurred within Fiji but virtually none where reproductive isolation is established, permitting cohabitation. Until the arrival of humans, perhaps 4000 and certainly by 3000 yr B.P., the vegetation was predominately rainforests with stunted cloud forest at high altitude, though some more open communities might have occurred in drier areas. The forests have a mixed species composition, including most of the 1769 native species, and demographic observations indicate peak population fecundities after several hundred years for canopy trees and 80 years for several subcanopy taxa. Flowering phenology of forest species is seasonal with predominately synchronous annual or, in a few species, biennial frequency, while fruit maturation is spread throughout the year. Cyclones cause frequent minor damage and infrequent major damage, especially to coastal and ridge vegetation, and cause landslides. Insect-induced dieback has been recorded but there are no extensive single-species rainforests, except swamp forests, so the effects are diffuse. The impact of humans has been to convert much of the drier forest to frequently burned sedge-fern-grasslands, to create garden-forest successional mosaics around settlements in wetter areas, and, more recently, to selectively log much of the remaining accessible forest. Many plants have been introduced and established in cultivated or disturbed areas, increasing the flora by about 50% and largely excluding native taxa from those areas. Habitat conversion is thus the major threat to the conservation of Fijian native vegetation.