晋北风沙特点、防风林带结构及效益

Characteristics of Dusty Wind in Northern Shanxi,Structure and Benefits of Windbreaks

晋北风沙区防风林带结构不合理、效益低下,风沙严重地段土壤风蚀量可达120～135m3/hm2。为对防风林带的设计提供理论支撑,研究在分析晋北害风发生规律、风沙性质和表层土壤机械组成的基础上,通过建立数学模型对防风林带设计的关键因子进行研究。结果表明:(1)晋北风沙区距地面1m高的起沙风速为3.2m/s,全年1m高度92.1%害风风速为3.2～6.4m/s,且集中出现在10月至翌年5月。(2)影响防风林带效益的主导因子为林带疏透度,晋北风沙区林带疏透度为0.3时,林带的有效防风距离最大,可达到林带高度的13.8倍。(3)以新疆杨、合作杨、油松和樟子松为主要树种营建防风林带时,林带最大间距分别为221,193,83,110m。(4)晋北风沙区害风具有分散性。害风风力率能综合体现害风出现的频率和强度,害风风力率最大时的林带走向为防风林带最佳走向。

Because of irrational structure and low benefits of windbreaks in northern Shanxi, the wind erosion quantity of the soil in severe section can reach as high as 120-135 m^3/hm^2. In order to provide a theoretical basis for design of windbreaks, based on an analysis of occurring rules of hazardous wind, characteristics of sandstorms and mechanical structure of topsoil in northern Shanxi, a research on key factors for design of windbreaks had been done by establishing mathematical models. The results are as following. （1）In wind dusty area of the northern Shanxi, the wind velocity of sand-moving is 3. 2 m/s at 1 m height from the ground; the velocity of 92.1% hazardous wind （the windvelocity is not less than 3.2 m/s at 1 m height from the ground） is 3.2- 6.4 m/s annually and they mainly occurred from October to May next year. （2）The dominant factor influencing benefits of windbreaks is porosity of the forest belt and when the porosity of the windbreak belt reaches 0.3 in the wind dusty area of the northern Shanxi, the maximum effective wind pre- vention distance of the shelterbelt can be 13.8 times of the height of the belt. （3）When taking Populus bolleana , Populus opera, Pinus tabulaeformis and Pinus sylvestris var. mongolica as main tree species to establish windbreak belts, the maximum spacing between belts is 221, 193, 83, 110 m respectively. （4）The hazardous wind in wind dusty area of the northern Shanxi is of dispersed nature. The wind rate of hazardous wind can reflect frequency and intensity of hazardous wind occurrence and the trend of the belt at the highest wind rate of the hazardous wind shall be the optimal trend of the windbreaks.