Yünnan Plateau

a highland in South China; the western and highest part of the Yünnan-Kweichow Plateau. The Yünnan Plateau includes most of Yünnan Province and is bounded on the north by the Yangtze River valley. The southern ranges of the Tahsüe Shan, which extend to China’s border with Burma, Laos, and Vietnam, are generally considered part of the plateau. The eastern and central sections of the plateau have elevations of 1,800–2,000 m. Mountain ranges in the west rise to elevations of 3,000–4,000 m.

The Yünnan Plateau is composed of ancient crystalline and metamorphic rocks, which are overlain for a considerable part of its length by Mesozoic limestones. There are deposits of tin in the Kochiu area and of phosphorites at K’unyang. The plateau is distinguished by a high level of seismicity. Weakly dissected plateaus predominate in the east; karst is widespread and includes “rock forests,” caves, and rivers that flow underground for part of their length. In the west the plateau becomes more deeply dissected. In places the main rivers—the Mekong, Salween, and Red River—cut through gorges 1–2 km deep. The principal mountain lakes are Tien Ch’ih, Fuhsien Hu, and Erh Hai.

The plateau has a subtropical monsoon climate, with most of the precipitation falling in summer. The average January temperature ranges from 4° to 10°C, and the average July temperature from 19° to 25°C. Annual precipitation, which is 1,000–1,500 mm on most of the plateau, exceeds 2,000 mm on the windward mountain slopes; the intermontane basins are arid, and their fields require artificial irrigation. Red earths and yellow earths, usually podzolized in the mountains, are the principal soil types. On the level areas, rice, tea, and fruits, including citrus fruits, are the main crops.

Forests occupy about 20 percent of the plateau. In the mountains there are tropical forests, with palms, Ficus, banana trees, ferns, orchids, bamboo, and numerous species of liana. At higher elevations the tropical forests give way to meadows and subtropical forests of evergreen and deciduous species of oak, schima, Castanopsis, and Yünnan pine. In several areas, the cutting of forests has resulted in secondary forest formations, including thin forests and savanna thin forests.