What are the causes of land desertification in central and western Jilin Province?

1. Natural factors 1. 1 Topography and geological structure determine the deep saline-alkali and sandy soil in the western region. Songnen Plain is a closed-flow plain with low and flat terrain, and the surrounding mountains are rich in precipitation, and a large number of soluble salts gather here. At the same time, influenced by medium, small and micro topography changes and special soil-forming conditions, it has a unique modern salt-forming process. Coupled with the high expansion of groundwater, saline-alkali land is fully developed and widely distributed, which is one of the areas where saline-alkali land is concentrated in China.

Songnen sandy land is distributed in alluvial plain, and Quaternary loose sediments are thick, generally 70~90? m？ , up to 100? m？ . Its upper part is 20~30? cm？ Loose sediments are mainly fine sand, silt and loam. These sediments provide sufficient sand sources for land desertification.

1.2 climatic factors. In recent decades, the temperature in the western region has gradually increased, the precipitation has decreased, and the wind speed has increased. Continental climate is obviously another factor in the development of desertification. Taking Qiqihar as an example, the average annual precipitation in Songnen sandy land in 1950s was 469.7mm? 433.2mm in the 1960s? 343.5 in the 1970s? Hmm? , decreased in 20 years 120.3? Hmm? . From 1950 to 1980, the annual average temperature gradually increased, and the temperature in 1970s was higher than that in 1950s 1.33℃. The precipitation in spring (March-May) only accounts for 10% of the whole year, and the evaporation is over 2000 mm. ..

It has been five years since 1995, except for the flood of 1998. Answer? Dry early, severe drought in the first half of 200 1, and there was no thorough rain in some places in early July. Drought and windy days provide dynamic conditions for desertification, and the annual number of windy days is 2 10 ~ 3 10d? . 30% of them are in spring, with an average wind speed of 3m/s? , the maximum wind speed is 30~40m/s? , April and May > 17.2? m/s？ The number of windy days is 4~ 13d? . Drought and lack of rain in spring, rapid rise of sand temperature, strong evaporation and bare ground accelerate the process of desertification.

2. Human factors

The main cause of land desertification in western China is people's unreasonable activities. Due to the rapid increase of population, food, fuel and living expenses are needed, so a large number of grasslands are reclaimed to grow grain, trees are cut down for fuel and livestock are raised in exchange for economic income. The continuous decrease of grassland leads to overload and overgrazing, resulting in alkalization, degradation and desertification. With the destruction of vegetation in sandy land, the originally fixed sandy land and sand ridges gradually become semi-mobile or mobile sandy land, which leads to serious deterioration of ecological environment. 2.2. 1 Destroy the grass and open up wasteland, the grassland will be reduced.

According to provincial records, in the early 1950s, the grassland in the former Baicheng area was 2. 13× 10hm2, and the hay yield was 1500~2250? From kg/ha to 1963, the usable area is reduced to 1.48x 106hm2, and the hay yield is reduced to 1000 hm2. According to the land survey in 1996, the available grassland area is 9.68× 10hm2, while the degraded, alkalized and desertified area is 1.09× 10hm2. During this period, the cultivated land (off the books) increased by 2.60× 10hm2.