With an area of about 400,000 km2 and an average altitude of between 1,000---2,000 m, the Loess Plateau is the third largest plateau in China and is mostly covered by a 50 ?80 m-thick layer of loess, which is incomparable in the world and a miracle of nature. is a plateau that covers an area of some 640,000 km² in the upper and middle of China's Yellow River and China proper . Loess is the name for the silty soil that has been deposited by wind storms on the plateau over the ages. Loess is a highly erosion-prone soil that is susceptible to the forces of wind and water; in fact, the soil of this region has been called the "most highly erodible soil on earth". The Loess Plateau and its dusty soil cover almost all of Shanxi, Shaanxi, and Gansu provinces, the Ningxia Hui Autonomous Region, and parts of others.
Geomorphology of Loess
The Loess Plateau has millions of gullies. The splendid loess pillars, peculiar peaks, cave dwellings and folk customs attract tourists from everywhere.
But the plateau has suffered from a serious loss of water and land erosion. Much of the loess is flushed away into the Yellow River by rain, filling it with mud and sand and carving out many gullies as it is carried away towards the sea. Research shows that exposed to thunderstorms, the porous loess can hardly avoid becoming eroded by the flowing water. This has been exacerbated by man-made devastation such as unreasonable land utilization and excessive deforestation. Now, the Chinese government is taking measures for reforesting some of the cultivated land and planting grass to control the loss of water and erosion.
This plateau was created two million years ago by the deposition of wind-blown dust and by glacial till, called loess, which was left behind by retreating glaciers. Loess provides good agricultural soil but is highly prone to wind and water erosion. High winds and lack of vegetation contribute to the dust storms that northern China is famous for. They also account for the distinctive color of the Yellow River and Yellow Sea. Because the fine grain "loess" soils areis easily eroded, much of this landscape consists of deeply furrowed yellow hills.
Vegetation in the northern loess plateau consists of broadleaved trees and is dominated by oak. Birch, maple, aspen, willow, and linden trees can be found at higher elevations, while elm and ash trees are found at lower elevations. Steppe vegetation increases gradually to the northwest. Very little natural vegetation remains on the loess plateau, as having been replaced by agriculture centuries ago. Vegetation has been planted to help stabilize the soil and reduce erosion, but for agricultural purposes rather than to restore natural forests. While tThere are protected areas within this ecoregion, mainly in the hills less suited for farming, but unfortunately they do not include loess areas.
Because the loess plateau is well suited to agriculture, natural forests were replaced centuries ago. With the loss of forest cover, erosion has increased and today has affected 45 percent of the area today.
At the southernmost edge of this ecoregion, near the Huang He in southern Shanxi Province, is Li Shan Nature Reserve. This reserve supports warm temperate forests that provide habitat for several rare animals, including rhesus macaques, musk deer, giant salamanders, and koklass pheasants. The Lu Lian Mountains of central Shanxi Province contain the Pangquan Gou Nature Reserve, a major breeding ground for brown eared pheasants and a stopover for migratory north China larks. Black storks, Mandarin ducks, and golden eagles are all protected here. The Luya Shan, another nature reserve in the Lu Lliang Mountains, also provides an important habitat for brown eared pheasants.
This vast plateau of some 154,000 square miles (400,000 square km) forms a unique region of loess-clad hills and barren mountains between the North China Plain and the deserts of the west. In the north the Great Wall of China forms the boundary, while the southern limit is the Qin Mountains in Shaanxi province. The average surface elevation is roughly 4,000 feet (1,200 metres), but individual ranges of bedrock are higher, reaching 9,825 feet (2,995 metres) in the Liupan Mountains. Most of the plateau is covered with loess to thicknesses of 165 to 260 feet (50 to 80 metres). In northern Shaanxi and eastern Gansu provinces, the loess may reach much greater thicknesses. The loess is particularly susceptible to erosion by water, and ravines and gorges crisscross the plateau. It has been estimated that ravines cover approximately half the entire region, with erosion reaching depths of 300 to 650 feet (90 to 200 metres).