United Nations Convention to Combat Desertification (UNCCD) defines desertification as "land degradation in arid, semiarid and dry subhumid areas". Nowadays, 36 million km2 of worldwide land in over 100 countries (Ci and Yang 9) and 20% of the global total population are influenced by desertification (11). China is affected by desertification more seriously than most of other countries. There is around 1.688 million m2 of national territory covering with "Gobi, sandy deserts, sandlands and sandified land"(Ci and Yang 177).
This research will investigate the distributions and influences of desertification, as well as the solutions for desertification in China. Desertification spreads through northeast, north, and west of China. Northeast China involves three provinces: Liaoning, Jilin and Heilongjiang (Fig. 1.1). Each province has been affected by desertification in various degrees.
According to data, collected in Desertification and Its Control in China, Jilin Province occupies the widest region of sandland among the three provinces with area of 494,107.8 ha (Ci and Yang 214). In Liaoning Province, the whole area of sandified land is 328,747.2 ha, which involves "197 townships of 18 counties" (Ci and Yang 213). The location of sandy lands in Heilongjiang Province is " at the eastern edge of a long stretch of blown sand", and the total area of desertification is 378,635.7 ha (Ci and Yang 215).
North China includes the municipality of Beijing and Tianjin, the province of Heibei and Shanxi, and Inner Mongolia Autonomous Region (Fig. 1.2). As recording, the distribution of desertification in Beijing can be divided into five regions that are mainly "along the river basins of the Yongding, Chaobai, and Wenyu Rivers," and the entire area is 58,012.2 ha (Ci 3
and Yang 210). There are 181,276.5 ha of sandland in Tianjin. In Hebei Province, sandified lands are located in 78 counties with area of 2,931,174.8 ha. Sandification is located in the north and northwest of Shanxi Province, "bordering with Shaanxi Province and Inner Mongolia (Ci and Yang 212)." Inner Mongolia, according to Circle of Blue expression, was one of the largest grasslands on the world. But now, a total area of 74,186,594.2 ha covers with desert.
Western China covers six provinces, Chongqing municipality, and the autonomous region of Ningxia, Tibet, and Xinjiang (Fig. 1.3). In three autonomous regions and three provinces, including Gansu, Qinghai, and Shaanxi, extensive deserts, Gobi, sandified land can be found. In Xingjiang, for instance, the whole area of desertified land is 76,920,460.3 ha of which "Gobi is 32,808,486.3 ha, sandy deserts cover 34,929,174.8 ha, and sandified land is 8,253,818.4 ha" (Ci and Yang 182). Similar to Gansu Province, Gobi, desert and sandified land respectively occupies 60.50%, 15.56%, and 23.42% of the total desertification area (Ci and Yang 199).
Fig. 1 Geographic map of provinces in Northeast China (1.1), North China (1.2), and Western China (1.3) 4 The influences of desertification are various. Sand-dust storm is one of the most serious natural disasters caused by desertification. For example, on 5th of May in 1993, the worst sand-dust storm affected four northern Chinese provinces (Futrell), which caused a huge amount of lost:
This storm ... buried or destroyed 35,000 ha crops, killed 8,000 head of livestock, buried more than 80 irrigation wells, damaged more than 100 sections of road and destroyed more than 200 livestock sheds and 100 houses. The direct economic loss from this storm was 176,000,000 RMB. (Ci and Yang 193) Sand-dust storm not only effects domestically but also overseas. According to W. Chad Futrell statement, in 2002, South Korea was engulfed by sand-dust from China and people, living in Seoul, gasp for breath for a long time.
Besides Sand-dust storm, desertification leads to silted lakes and changes flow of rivers. Qinghai Lake, for instance, has been threatened by shifting sand for many years. In past decades, because sediment went into the lake, the level of water decreased by 12.22 m and the exposed region of lake bed rose to 359.4 km2 (Ci and Yang 207). The amount of water reduced year by year as well. Ci and Yang express that China has witnessed the longest inland river, the Tarim River, has been dry for more than ten years and 160 km of river course in Xinjiang has been buried by sand (187).
How to combat desertification? Chinese government has already accumulated rich experiences and various control measures (Ci and Yang 428).Vegetation is often viewed as an appropriate measure to control desertification because vegetation prevents the drylands from expanding and weaken the drought winds (Ci and Yang 368). There are many successful vegetation projects, such as Three North Shelterbelt Network Project. So far, the 5
project has reached the purpose of increasing the plants coverage by up to 14.95% (Ci and Yang 368).However, Fan and Zhou argue that because vegetation " will not have the required effect on decreasing and eliminating population pressure on the desertified land ... , the planting of trees and grasses has very little or no significant effect".
In arid area, enclosure is another often-used measure to prevent desertification and to improve the degraded vegetation (Fan and Zhou). Enclosure contains three types: "complete enclosure, partial enclosure and rotational enclosure" (Ci and Yang 376). The results of enclosure are related to the appropriateness of the enclosure measures, so Ci and Yang suggest using flexible enclosure methods, properly opening the enclosed area, and strengthening management system (379).
According to the research of Chen, the quantity of species, the coverage of fresh grass, and the height of grass layer were increased through the whole enclosure period, which was from 1982 to 1999 (Table 1). Despite the effectiveness of enclosure, there are some limitations. Fan and Zhou point out that although desertification can be reversed in enclosed pastures, outside enclosure might be exacerbated.
Table 1 Changes of different plant communities in enclosure region
6 In addition to biological measures, mechanical approaches, including "construction of sand barriers, chemical mulching, and hydrologic solutions", have been developed to combat desertification in China (Ci and Yang 428). Mechanical barriers are designed to change direction and velocity of wind and to minimize influences of denudation and erosion (Ci and Yang 432).
The purpose of chemical mulching is to stabilize shifting sands by spraying chemical materials (Ci and Yang 438). Hydraulic engineering is built to manage and relocate surface water and ground water (Ci and Yang 440). In recent decades, throughout China, mechanical measures have been adopted, practiced, and reformed.
This research demonstrates wide distributions and damaging impacts of desertification, as well as biological and mechanical solutions for desertification in China. China is one of the developing countries with vast desertified areas and Chinese government is aware that influences of desertification are disastrous. This research suggests that Chinese authorities ought to keep combating desertification and they should also adopt voices of doubt.