Six major rivers drain Tibet and western China: Yellow (Huang), Yangtze (Jinsha), Mekong (Lancang), Salween (Nu), Bramaputra (Tsangpo) and Indus (Sengge). Their sources are at elevations of 17,000 to 18,000 ft. Within western China, the Mekong and Salween drop to elevations on the order of 2,000 feet. The other rivers leave the region at much higher levels - typically above 6,000 ft.
Elevation, which generally determines the range of temperature, is one of the major determinants of the type of ecosystems that occur. Another major determinant is precipitation. In Tibet and western China, most precipitation is due to summer and fall monsoons moving north from the Indian Ocean, particularly via the Bay of Bengal east of India and to a lesser extent via the Arabian Sea west of India. The Himalayas produce a rain shadow over most of Tibet, which, combined with the high average elevation (15,000 feet), results in a high desert ecosytem. Latitude is also another major determinant of ecosystem type. Latitudes in this region range from about 40 N to 22 S. High desert ecosystems occur at the northernmost extent and tropical rainforests occur at the southernmost extent. For example, the Mekong begins at a glacier on the Tibetan Plateau where there is virtually no vegetation and passes though tundra, then shrubs and pinyon-juniper forest, then temperate pine and deciduous forest and finally into tropical rain forest before passing into Myanmar.
Tibet and western China, which occupy about 35% of the land mass of China, account for well over half of all plant and animal species found in China. This region is also the source of much of China's water supply and increasingly of its natural resources. The development of resources such as hydropower, mineral extraction, timber and wildlife harvesting and animal husbandry (grazing) and the associated increase in human population have had significant impacts on many of the ecosystems of the region.
Overgrazing effects are obvious on the far hill side.
Although these impacts are expanding, efforts are being made to mitigate and in some areas to eliminate them. The Chinese have established large nature preserves in northwestern Tibet (Chang Tang) and northwestern Sichuan (Wolong Panda), national parks in Yunnan (Great Rivers and Xishuangbanna) and in the central and eastern Himalayas (Everest and Namchibarwa), they have limited or eliminated logging, hunting and certain types of plant gathering in many parts of the Hengduan Mountains, and they are slowly attempting to reduce loss of soil from overgrazing in the headwaters areas of these rivers and to reduce water and air pollution from mining. After the disasterous floods of 1998, they recognized that uncontrolled development of natural resources can have dire consequences on both the local ecosystem as well as human and natural ecosystems more than a thousand miles downstream.
Another major reason to protect the natural ecology of this region is ecotourism. As the disposable income of Chinese citizens increases and as China continues to open its doors to foreign business, there is an increasing demand for visits to relatively undeveloped areas of this region, by both Chinese and foreign tourists.
Ecology of the Tibetan Plateau
Elevations on the Plateau range from about 10,000 feet to over 20,000 feet, with an average of 15,000 feet. Typically, trees don't grow above about 12,000 feet, so the great valleys of the Plateau are grasslands. Mountains above about 17,000 feet are generally barren, and pinyon pine, juniper and scrub oak grow in canyons below about 12,000 feet. The rainy season is mid July through September, then winter begins.
Wild large grazing mammals such as yak (drong), antelope (chiru) and blue sheep (bharal) were once abundant but populations have declined significantly due to hunting and overgrazing. Populations of their major predators (wolves and snow leopards) have also declined, due both to reduced food supply and hunting. Consequently, the most common wild animals on the plateau are small mammals such as marmots, rabbits and picas, eagles and hawks which prey on them, migratory birds, and vultures. Some of the great lakes on the Plateau are favorite sites for bird watching in the spring and fall. Large vulture populations are sustained by the Tibetan practice of sky burials.
The domestic yak is probably the most common large mammal on the Tibetan Plateau. Recent estimates suggest a population of more than four million, followed by domestic sheep and goats. In many areas, their trails criss-cross hill slopes and overgrazing has caused extensive soil erosion and landslides. As a result, the soil no longer holds as much water so rainfall flushes into rivers, aggravating flooding, and stream flows are lower during the dry season.
To help mitigate the negative effects of overgrazing and to help preserve endangered large mammals, the Chinese, with the support of Tibetans, have instituted policies reducing both human and domestic animal populations in the headwaters of the Yellow, Yangzte and Mekong drainages in southwest Qinghai and have created large wildlife preserves in the Chang Tang in western and northern Tibet.
Ecotourism is currently undergoing a dramatic raise in popularity in this region. There are dozens of travel agencies that offer trekking tours to Qomolangma (Everest) National Park and Mt. Kailash in western Tibet in addition to numerous other areas, and Wind Horse Adventures has begun offering whitewater rafting and kayaking trips in the Lhasa area. To support this influx, the Chinese are building a railroad from Golmund in western Qinghai south to Lhasa, which is expected to be completed by 2007. In addition to tourists, the trains will carry supplies for development and propane to replace the yak dung that is currently the primary source of fuel for nomads. The idea is that decaying yak dung will augment revegetation in areas of heavy grazing, thus reducing the pressure to relocate people.
In addition to the airports in Lhasa (central Tibet), Yushu (southwestern Qinghai) and Qamdo (northeastern Tibet), the Chinese are also building a new airport in southeastern Tibet and have plans to build one in western Tibet, plus they are rapidly improving and expanding the roads on the Tibetan Plateau. They also have plans to build a major dam on the Yarlung Tsangpo in southeastern Tibet (the Great Bend area) and to divert water from the headwaters of the Yangtze to the headwaters of the Yellow River in central Qinghai. Currently there are two canals that carry water north from the Yangzte (one in central China, the other in eastern China), but the Yellow is badly overallocated compared to the Yangtze and from an engineering perspective the cost of diverting water in the headwaters is the most appealling.
Stupas in a pinyon-juniper forest
Ecology of the Shrublands and Pinyon Forests
This is a transition zone that typically occurs from about 12,000 ft to 10,000 feet, depending on proximity to the rain shadow of the Himalayas and exposure to the sun - it extends to lower elevations on south facing slopes. It primarily occurs on steep slopes in the canyons of the Salween, Mekong and Yangzte as they drop off the eastern side of the Tibetan Plateau. The rainy season is early July to September, then winter begins.
Grasses and wildflowers thrive in the spring and during the summer monsoons, and where water is available villagers raise yak, sheep and goats. However, due to the fact that shrubland and pinyon forest slopes are typically steep, overgrazing in this zone often results in landslides with total loss of the thin soil zone and its vegetation. Throughout eastern Tibet and western Sichuan, this zone has suffered great damage due to overgrazing. Unfortunately, with the exception of the canyons of the Salween, Mekong and Yangtze in northwestern Yunnan where some degree of protection may be afforded by Great Rivers National Park, little has been done to mitigate the problem of overgrazing.
Doxong La in southeastern Tibet
Ecology of the Pine and Temperate Deciduous Forests
This zone occurs mostly in the deep canyons of the Tsangpo in southeastern Tibet, the Salween and Mekong in northwestern Yunnan and in large tributaries to the Yangtze in western Sichuan such as the Yalong and the Dadu. Elevation ranges from about 10,000 feet to as low as 4,000 feet in southeast Tibet and northwest Yunnan. The rainy season is from June to October, then fall begins. It is home to a great variety of wildlife such as the famous Great and Red panda bears, and has been seriously impacted by logging.
This mud slide on the Yigong River in eastern Tibet was caused in part by poor logging practices. When lake that formed behind it eroded the mudslide in 2000, the resulting flood closed the main highway between Lhasa and Chengdu (Sichuan) for two years.
Fortunately, the Chinese have recognized the need to preserve the habitat of the pandas and other endangered species of this region, and have established Wolong and other panda preserves west of Chengdu, Sichuan and Great Rivers National Park northwest of Lijiang in Yunnan. They have also begun to limit logging and hunting in many areas of southeastern Tibet, southwestern Sichuan and northwestern Yunnan, and the Nature Conservancy has been helping villagers develop biogas generators to reduce the need to collect firewood for fuel. To encourage tourism, they have built airports at Zhongdian (renamed Shangri La) and Lijiang in southwest Sichuan, they are rebuilding roads and are building a new railroad from Chengdu to the Yangtze.
One of the consequences of these changes is loss of jobs and impoverisment in the affected regions. The Sichuan, Tibet and Yunnan goverments are making major investments in the infrastructure necessary for ecotourism, with the hope that eventually service jobs will develop to replace resource extraction jobs. Hopefully, some of the new service jobs will be for professional river guides. Frequently, long term protection of river ecosystems follows the development of an economy based on ecotourism.
Ecology of the Tropical Rainforests
This environment occurs only in southwestern Yunnan, in the region of the Mekong and Salween where they pass into Myanmar. Here the latitude is south of the Tropic of Cancer (23.5 N) and elevation is typically below 4,000 feet (so frosts are rare), and monsoons arrive in May and stay until October or November. One of the oldest national parks in China, Xishuangbanna, is located on the west bank of the Mekong in this area and is home to many endangered species, including elephants, tigers and monkeys. The Chinese built an airport in Simao in the 1990s to provide tourist access to this area. Here the Mekong is wide and flat, and tourists can explore the area in motorized boats.
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