Indochina subtropical forests
Indochina subtropical forests form a unique biome located in the highlands of northern Myanmar, Laos, Vietnam, and southern Yunnan in China. Characterized by diverse landscapes, the region features mountainous terrain with elevations often exceeding 6,600 feet, and river valleys that nurture a range of ecosystems. The climate is influenced by summer monsoons, delivering significant rainfall and creating distinct seasons, including a cool, dry period. This diversity in climate and geology supports a rich variety of flora, including subtropical broadleaf evergreen forests and unique montane communities, which host endemic plant species.
The fauna of these forests is equally varied, home to several endemic mammals and birds, including critically endangered species such as the Tonkin snub-nosed monkey. The biome is essential for larger wildlife, including the Asian elephant and the Indochinese tiger, both of which face significant threats from habitat loss and poaching due to human activities. Conservation challenges are exacerbated by agricultural expansion and the demand for cash crops, which fragment the forests and diminish vital habitats. Despite its ecological importance, there is a pressing need for further research to understand the impacts of climate change on these sensitive ecosystems.
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Subject Terms
Indochina subtropical forests
- Category: Forest Biomes.
- Geographic Location: Asia.
- Summary: This biome has diverse fauna, with several endemic species. Because of land conversion from forest to agriculture and hunting, many plants and animals here face an uncertain future.
The Indochina Subtropical Forests biome consists of forests across the highlands of northern Myanmar, Laos, Vietnam, and the southern Yunnan province of China. The landscape is mountainous, with hills and river valleys extending from Yunnan into the northern Indochina region. These river valleys contain the middle catchments of the Red, Mekong, and Salween Rivers. Intrusive igneous rocks and Paleozoic limestone are dominant parent material in these areas. Mountain ranges here generally peak around 6,600 feet (2,000 meters) in elevation, with the river valleys at elevations of 656–1,312 feet (200–400 meters). The Yunnan Plateau can reach as high as 9,840 feet (3,000 meters), however.
The climate in northern Indochina is dominated by summer monsoons that bring 47–98 inches (1,200–2,500 millimeters) of rain annually. The monsoon brings much of the annual precipitation from the Bay of Bengal and South China Sea from April to October. The entire region, including the Yunnan Plateau, has an extended cool and dry season from November to April. The spring pre-monsoon (April to May) is the warmest time of the year; January is the coldest. Frost forms infrequently and only at high elevations.
Vegetation
The unique climate and geology of this region have given rise to lush, diverse forests. This biome has tropical, subtropical, and temperate groups of plants with distinct origins; these floristic groups are: Indian, Malesian (or Sundaic), Sino-Himalayan, and Indochinese. At lower elevations of 1,970–2,625 feet (600–800 meters), subtropical broadleaf evergreen forests contain trees of the dipterocarp, birch, oak, and zapote families.
At higher elevations of 2,625–6,600 feet (800–2,000 meters), a distinctive moist montane broadleaf forest exists, with communities dominated by species of the oak and laurel families, over an understory of small-statured bamboo and ferns. Much higher in elevation on the Yunnan Plateau, Yunnan pine (Pinus yunnanensis) is dominant in open-canopy forests. In northern Vietnam, elevations greater than 6,600 feet (2,000 meters) have a unique fir-and-hemlock community that contains species from the maple, oak, magnolia, and laurel families.
The vegetation in this ecoregion is generally shaped by the monsoonal precipitation and the dry season; some evidence suggests that lower-elevation seasonal forests are adapted to frequent low fires. Phonix palms, for example, are well adapted to survive ground fires. The level of natural frequency of fire is difficult to predict currently, as most present-day fires are human-caused (anthropogenic). At higher elevations, open-canopy pine forests on dry slopes are also thought to burn periodically. There is speculation that the forest species composition would be quite different without the anthropogenic fires.
Wildlife
This biome boasts diverse fauna, with several endemic (found nowhere else) mammals and birds. Notable endemic and near-endemic mammals are a species of slow loris, the white-cheeked gibbon, Ouston’s civet, Roosevelt’s muntjac, Tonkin snub-nosed monkey, and Anderson’s squirrel. Once thought to be extinct, the Tonkin snub-nosed monkey is critically endangered, with fewer than 250 individuals remaining.
The region boasts several iconic species such as the Asian elephant; the Indochinese tiger; and the smallest of all bears, the Malayan sun bear. Once found across the ecoregion, Indochinese tigers are extinct in the Yunnan province and number fewer than 350 individuals elsewhere. Other notable animals are two wild cow species (gaur and banteng), southern serow, pygmy loris, Asian black bear, clouded leopard, Asiatic wild dog, black striped weasel, smooth-coated otter, and three macaque species.
The region has diverse avifauna, including the near-endemic short-tailed scimitar babbler. Several pheasant and hornbill species need intact mature forests. Hornbills, which eat large fruits, play a critical role in dispersing the seeds of large-seeded mature forest trees and liana species. This region has healthy populations of white-rumped and slender-billed vultures, which have declined dramatically elsewhere in southern Asia.
Environmental Threats
The Indochina Subtropical Forests ecoregion has several conservation challenges. Shifting cultivation agriculture has been practiced here for millennia. Overexploitation and conversion to agricultural land remain large threats. Cash crops like sugar, rubber, and palm oil are a crucial part of the area's economy and require large swaths of land for growing purposes. With the human population rising, the proportion of cleared land has increased, leaving less land for the forest to regrow. In recent years, the forests have become fragmented, especially at lower elevations, as elsewhere in the tropics. Consequently, habitat is declining for species such as tigers, elephants, gaurs, and bears that need large intact forests or forests connected with landscape corridors.
Hunting is a critical component of local cultures, and game provides important protein in human diets. International demand for animal parts needed in Chinese traditional medicine has also contributed to poaching. Tigers are especially vulnerable, as tiger body parts are highly prized and sought after for Chinese traditional medicine. As a result, conservationists have identified “empty forest syndrome,” wherein the current forest structure, largely dependent on adult trees, remains visibly unaffected—but many of the animals that exert critical herbivory and predatory roles for future forest structure are gone from the area.
Despite this region’s biodiversity and the important ecosystem services it provides, such as watershed protection for the Mekong River and its delta area, the effects of climate change on the forests of this region are poorly understood. More research is needed to help predict looming changes in temperature, moisture, storm patterns, fire regime, and seasonal cycle timing.
Bibliography
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Gaisberger, Hannes, et al. ‘Tropical and Subtropical Asia's Valued Tree Species Under Threat. Conservation Biology, vol. 36, 2022, doi.org/10.1111/cobi.13873. Accessed 19 Nov. 2024.
Pimm, S. L., et al. Terrestrial Ecoregions of the Indo-Pacific: A Conservation Assessment. Washington, DC: Island Press, 2001.
Sharma, Eklabya, et al. Climate Change Impacts and Vulnerability in the Eastern Himalayas. Kathmandu, Nepal: International Center for Mountain Development, 2009 .
Sterling, J. E., et al. Vietnam: A Natural History. New Haven, CT: Yale University Press, 2006.