Solomon Islands Rainforests

Category: Forest Biomes.

Geographic Location: Pacific Ocean.

Summary: The Solomon Islands rainforests, although home to a limited number of species of mammals, birds, and amphibians, have an unusually large proportion of endemic species.

The Solomon Islands is a sovereign state consisting of more than 1,000 islands located in the Pacific Ocean, east of Papua New Guinea. Most of the Solomon Islands are part of the Solomon Islands Rainforest biome. Because of the isolation of this island chain, and the rugged topography and the lushness of the habitats here, a full range of endemic (found nowhere else) species of flora and fauna live in these tropical rainforests.

The oceanic-equatorial climate here provides a mean temperature of 80 degrees F (27 degrees C) throughout the year, with few extremes of temperature, although the June-through-August period has slightly cooler weather than the rest of the year. While most of the Solomon Islands are within the Solomon Islands Rainforest biome, the Santa Cruz Islands group makes up part of the somewhat different Vanuatu Rainforests ecosystem.

Soil quality in the Solomon Islands rainforest varies greatly, from rich volcanic soil to infertile limestone. The climate here is considered tropical wet; the ecosystem is comprised chiefly of tropical lowland and montane forest habitats. Although most land on the islands lies below an elevation of 3,000 feet (914 meters), the predominant terrain type is forested hills.

Flora

Seven broad vegetation groups exist in the Solomon Islands, including coastal strand vegetation, freshwater swamp forests, mangrove forests, montane rainforest, two types of lowland rainforests, seasonally dry forest, and grasslands—this latter type found only on the large island of Guadalcanal. The lowland rainforest is the most common plant community.

The lowland rainforest canopy tends to be uneven, as frequent natural disturbances such as subsidence, fallen trees, and tropical storms disrupt it. Six diverse lowland rainforest types are spread about the Solomon Islands, resulting from a forest’s location on the northern or western side of an island, its elevation, and the local level of disturbance.

A variety of common tree species exist here; among the most common are penaga (Calophyllum kajewski), kamani (C. vitiense), the fruit-bearing sumac (Campnosperma brevipetiolata), sea bean (Maranthes corymbosa), beabea (Schizomeria serrata), elephant apple (Dillenia solomonensis), the deciduous whitewood (Endospermum medullosum), and the eucalypt black wattle (Gmelina mollucana). Other important plants include the many endemic orchid and palm species.

Fauna

As true oceanic islands, the Solomon Islands are home to a high number of endemic vertebrates. The rainforests have fewer mammals than other nearby regions, such as New Guinea to the west, but there is a large gallery of bats here. The Solomon Islands rainforests are thought to contain fewer than 50 mammal species. At least half of these are endemic to the biome, including nine rodent species; 15 species of family Pteropodidae, or old-world fruit-eating bats; a free-tailed bat of genus Molossus; and the Solomons horseshoe bat (Anthops ornatus).

A similar pattern holds with avian species: relatively low diversity but high rate of endemism. The Solomon Islands rainforests are a haven to more than 40 families and subfamilies of birds, with perhaps 200 species. More than one-third of these are endemic to this ecosystem, a factor making the Solomon Islands rainforests a critical global area for bird conservation.

Among the endangered rainforest bird species found here are Woodford’s rail (Nesoclopeus woodfordi), Makira moorhen (Gallinula silvestris), chestnut-bellied imperial pigeon (Ducula rubricera), white-eyed starling (Aplonis brunneicapilla), and imitator sparrowhawk (Accipiter imitator).

Environmental Threats

Direct human alteration of riverine and coastal areas, along with typically poor soils in some areas, have contributed to the depletion of lowland Solomon Island rainforests, and fragmentation of remnant coastal swamp vegetation and pandanus thickets. Some of the outlying coral atolls of the archipelago are in better native condition than the larger islands. While timber is the nation's most significant export, illegal logging strips the land of trees, carves logging roads through sensitive habitats, and allows the rains to wash away the mountain soil. Such devastation has negative effects on communities as well when they lose their natural resources. Corruption of local and national authorities makes stopping such operations nearly impossible.

The rainforests are subject to tropical cyclones from November to April; these storms have proved to be sources of natural disturbance to flora and fauna, as have extreme droughts, which occur with some regularity, generally on a six- to 20-year cycle. However, climate change impacts upon this region, already prone to major storms and droughts, could push some habitats here beyond tipping points that have evolved over thousands of years.

Bibliography

Beck, John. "Logging Is Corrupting These Islands. One Village Fights Back--and Wins." National Geographic, 3 Jan. 2020, www.nationalgeographic.com/science/article/deforestation-in-the-solomon-islands?loggedin=true. Accessed 1 Sept. 2022.

Bennett, Judith. Pacific Forest: A History of Resource Control and Contest in Solmon Islands, c. 1800-1997. Brill, 2021. Print.

Gillespie, A. and W. C. G. Burns, eds. Climate Change in the South Pacific: Impacts and Responses in Australia, New Zealand, and Small Island States, Vol. 2. Dordrecht, Netherlands: Kluwer Academic Publishers, 2000.

McKibben, B. Deep Economy: Economics as if the World Mattered. London: Oneworld Publications, 2007.

Wolff, T. “The Fauna of Rennell and Bellona, Solomon Islands.” Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 255 (1969).