Research On Sand-dust Control Mechanism Of Vegetation At The Northeast Edge Of Ulan Buh Desert

Study on laws of wind-blown sand movement and plant function mechanism is an important part of desert research. The technical route of this study is to study the characteristics of wind-blown sand movement and sand-dust control mechanism of plants with blown sand physics and mathematical statistics as basic principles, combining theories of forestry, ecology and other subjects. The objection is to provide theoretical base and scientific methods to control blown sand hazard and improve the eco-environment in north China.Based on summary of the research fruits of predecessors, with experiments outdoors and investigation at the northeast edge of Ulan Buh Desert, this paper analyses data of dust and sand weather; spot observation and investigation outdoors were done on wind erosion, wind-sand activity, dustfall, soil of different layers, and particle characteristics of dustfall; this paper also studies the whole system composed of blown sand moving process mainly with parallel movement and particle falling process mainly with vertical movement. After analysis and study, initial results were got as following:(1) The atmospheric circulation at the northeast edge of Ulan Buh Desert is effected by the cold air from northwest of our country. The average number of sandstorm days in a year is 10.79, so it is a frequently-occurring area of weather such as strong wind, blowing-sand and sandstorm. In this area, the characteristic of sandstorm distribution in the recent 33 years is the general trend of wavily descending, and the fluctuation range obviously affected by the rainfall the year before. In one year, the number of sandstorm days is the biggest from March to May, which is 60.2% of that of the whole year; in one day, the number of sandstorm times is biggest from 14:00 to 20:00, which is 69.57% of the total.(2)In the near-surface range of 0-40cm, When wind velocity is the same, sand transport in the morning is obviously less than that in the afternoon, and the difference can decrease with wind velocity. Relative sand-dust content on fixed sandy land has a logarithmic function to the distribution of height. With the decrease of vegetation coverage, relative sand-dust content has various functions to the distribution of height. On semi-fixed sandy land, when wind velocity is low, relative sand-dust content has a logarithmic function to the distribution of height; when wind velocity increases to some degree, the relation of relative sand-dust content and distribution of height changes to power function. When the vegetation coverage continues decreasing to the degree of shifting sandy land, nomatter how the wind velocity varies, relative sand-dust content has only an exponential function to the distribution of height. The relation of wind velocity and total amount of sand transport also changes with vegetation coverage: On shifting sandy land, wind velocity has a cubic function to the sand transport; on semi-fixed sandy land, wind velocity has a power function to the sand transport; on fixed sandy land, the relation curve of wind velocity and the sand transport is an exponential function.(3)The time distribution characteristic of dustfall is that the amount of dustfall increases from January, reaches the maximum in April, then gradually descends to a low value in August, September and November, and that dustfall amount each month is obviously in positive correlation with days of strong wind. The amount of dustfall in the whole year varies clearly with vegetation conditions, which is the largest in open land, then in shrubby forest, and the smallest in tree windbreak of the second experimental farm. Its characteristic of spatial distribution is that in open land, Hedysarum scoparium shrubby forest, Ammopiptanthus mongolicus shrubby forest, and the tree windbreak of different sizes in the second, third and fourth experimental farms there are always evidently more dustfall 2m high than that 5m high, and the maximum gap occurs in April.(4)In this research, it is also discovered that the sand-dust sources can be divided...