Hainan Island monsoon rainforests
Hainan Island, located in the South China Sea, supports extensive monsoon forest in its seasonally dry interior. Many endemic taxa have evolved here, and forest types resemble those found in the hilly regions of northern Indochina. Today, this ecoregion has been heavily affected by conversion of land to both subsistence and commercial agriculture, so that the Hainan Island monsoon forests include some species that are nearly extinct.
Location and General Description
The second largest island off the coast of China, Hainan is located in the tropics at about 18 °N latitude and is separated only by a short distance from the Leizhou Peninsula, Guangdong Province. Because Hainan has been an island only since the Quaternary era, it does not have as many endemic genera as might be expected on an older, oceanic island. However, it does support many endemics at the species level.
This island includes two ecoregions. The coastal plains, where rainfall is more evenly distributed over the course of the year, are part of the extensive South China–Vietnam Subtropical Evergreen forests ecoregion. The interior upland, dome mountains, 500 to 1000 meters (m) in elevation or more, support Hainan Island Monsoon forests. This ecoregion is associated with the hotter and drier interior of the island where significant drought stress during the pre-monsoon affects the character of the forest. Dominant trees here tend to be deciduous with an understory of grass beneath the thin canopy.
Hainan has a moist monsoon tropical climate that brings rain with the northward movement of humid equatorial air during summer, and clear weather with the southward movement of cool dry air off the Asian continent during winter. Annual precipitation averages 2,000 millimeters (mm) on the east coast and about 1,000 mm on the west coast. Typhoons from the South China Sea also sometimes hit the island. Temperatures are warm during most of the year, although sea breezes prevent extremely warm conditions. During winter, cold air masses from China can cause temperatures to fall below 3 °C.
The island’s drought deciduous tropical monsoon forests are dominated by tree species that drop their leaves in the pre-monsoon, a phenological pattern that is common to the interior plains and low hills over much of Indochina. These tree species include Kleinhovia hospita, Spondias pinnata, and Tilia hainanensis. Evergreen trees also occur in this area, especially on shaded slopes that have more retentive soils, and at slightly higher elevation. These include Diospyros potingensis and Meyna hainanensis. The driest parts of the island interior support a savanna of the acacia-like legume, Albizzia procera.
Because the canopy is thin, light is sufficient to support a closed cover of grasses in the understory of these drought deciduous forests. This, in turn, leads to an increased frequency of ground fire, although it is a matter of some controversy as to whether fire is a natural component of this ecosystem, or whether the increased fire frequency observed here is a phenomenon that should be attributed solely to human activity. At any rate, fires remove nutrients from the soil surface as they burn quickly through the understory. This prevents a humus layer from accumulating, which, in turn, prevents the soil from attaining a water-holding capacity sufficient to enable more mesic, shade-producing tree species to establish themselves. Grass continues to flourish and burn frequently, encouraging its own replacement. Thus, feedback within the system maintains the drought deciduous condition of forest.
Montane evergreen broad-leaved forest occurs at higher elevations (1,000 to 1,600 meters [m]) in the interior of Hainan Island. Forests here are similar to those of subtropical habitats throughout Asia, dominated by Castanopsis spp., Lithocarpus spp., Lauraceae, and Schima spp. Montane cloud forests occur near the summits of the highest peaks at elevations above 1,600 m.
Hainan has a generally high biological diversity with 4,200 plant species, 630 of which are listed as endemic to the island. Researchers have recorded 98 mammals and 291 bird species, although many of these birds are species that winter along the coast and should not be included within the avifauna of this highland ecoregion.
A surprisingly high diversity of conifer species occurs in the interior uplands. Two of the more abundant are the tropical taxa, Dacrydium pierrei (a threatened species) and Podocarpus imbricata. Other threatened conifer taxa that have been recorded from Hainan include Cephalotaxus hainanensis, C. mannii, Keteleeria evelyniana, Pinus fenzeliana, P. latteri, P. massoniana ssp. hainanensis, and Podocarpus annamiensis.
Two mammal species, the Hainan moonrat (Neohylomys hainanensis) and Hainan flying squirrel (Hylopetes electilis) are endemic to Hainan. There is some controversy as to whether the Hainan moonrat, an endangered species, is an endemic genus or whether is should be placed with the other Hylomys moonrats. These creatures, small members of the hedgehog family Erinaceidae, frequently search for prey in water, feeding on a range of crustaceans, mollusks and fish. Most species will also feed on fruit and berries. Other notable mammal species include the thamin, an endemic subspecies of Eld’s deer (Cervus eldi hainanus), black gibbon (Hylobates concolor), Asiatic black bear (Selenarctos thibetanus), and Hainan mole (Talpa insularis).
The island includes an Endemic Bird Area that is roughly congruent with this ecoregion. It supports two endemic bird species, the Hainan leaf warbler (Phylloscopus hainanus), which is listed as vulnerable, and the Hainan partridge (Aborophila ardens), listed as endangered. The Hainan partridge is now restricted to only a few patches of remaining evergreen forest. Other restricted-range bird species are the ratchet-tailed treepie (Temnurus temnurus) and white-eared night heron (Gorsachius magnificus), considered critical. The latter species has not been sighted for more than 30 years and may be extinct. According to Birdlife International, there are about 46 subspecies of birds endemic to Hainan, several of which may be better regarded as full species. Two other threatened bird species occur on Hainan, but these have a wider range. They are the pale-capped pigeon (Columba punicea) and Blyth’s kingfisher (Alcedo hercules), both of which are considered vulnerable.
Many small nature reserves have been designated in the drier, interior portions of Hainan Island, but these tend to be degraded and lack connectivity with other nature reserves.
Hainan has been subjected to a great deal of deforestation, both recent and historical. For example, by 1949, forest cover had been reduced to about 25 percent. In 1981, the remaining forest cover on the island was only 7.2 percent. All four of the restricted-range bird species found on Hainan are threatened by habitat loss. Hainan partridge is also threatened by hunting.
Types and Severity of Threats
Rubber plantations occupy much of the island area, as do oil palm, coffee and others. Agriculture is practiced intensively in some areas. In other areas, however, slash-and-burn cultivation is used, especially by the minority Miao and Li people who inhabit the less productive upland parts of the island. Slash-and-burn is an inefficient way to grow food, because a large area of forest is converted to scrub land, and only a small proportion is utilized in any given year. This form of shifting cultivation may be sustainable if it is practiced on suitable slopes (not too steep) with a long rotation period (sufficient to regenerate forest between cuttings) but, all too often, the system breaks down under population pressure and the result is degradation of large areas of upland landscape.
Deforestation on Hainan is accompanied by a high risk of extinction, as the forests support many species about which little is known regarding abundance and distribution. To date, 45 of Hainan’s 4200 plant species are listed as endangered. About 450 tree species are harvested for timber, and some could become extinct if current rates of deforestation continue.
- Chinese Vegetation Map Compilation Committee. 1979. Vegetation map of China. Map (1:10,000,000). Science Press, Beijing, China.
- Diamond, J.M. 1975. The island dilemma: lessons of modern biogreographic studies for the design of natural reserves. Biological Conservation, 7:129-146.
- MacDonald, D. editor. 1999. The Encyclopedia of Mammals. Barnes and Noble Books. ISBN: 0760719411
- MacKinnon, J. and K. Phillipps. 2000. A Field Guide to the Birds of China. Oxford University Press, New York. ISBN: 0198549407
- Mackinnon, J., M. Sha, C. Cheung, G. Carey, Z. Xiang, and D. Melville. 1996. A biodiversity review of China. World Wide Fund for Nature, Hong Kong.
- 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: 1560985747
Disclaimer: This article contains information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.