北方旱区农田防护林防风效应研究

Study on windbreak effect of farmland shelterbelts in dry farmlands of North China

【目的】揭示防护林带的疏透度(β)、宽度、高度、风向与林带夹角等因子对农田防护林防风效应的影响。【方法】利用PC-3型便携式可移动自动气象站,采用多点观测方法对干旱、半干旱土壤风蚀区的林带结构和防风效应进行调查,分析不同林带疏透度、宽度、高度以及风向与林带夹角对风速变化的影响。【结果】稀疏型结构的林带防风效应最佳,最高达34.27%,平均为32.69%;疏透型次之,为25.12%;通风型最差,为20.98%。β为0.30~0.50的林带防风效应最佳,且林冠层和林干层疏透度存在差异时防风效应较好。风向与林带夹角的正弦值与防风效应呈正相关;β为0.30~0.50时,宽度为2H^5H(H为林带平均高度)的林带防风效应相差不大,超过5H时林带的防风效应随其宽度的增加而迅速减弱;当气流进入林网区域后,风速在前4条林带呈减弱趋势,减弱幅度最大的是第1条林带,在第4条林带后风速开始恢复。【结论】林带的疏透度、宽度、高度和风向是决定单条林带防风效应的主要因子。

【Objective】The study was done in order to reveal the effect of the factors of windbreak porosity,ventilation coefficient,shelterbelt width and tree height of shelterbelts et al on the movement and changes of wind speed in field.【Method】PC-3 portable automatic weather station was used to observe shelterbelt structure and windbreak effect in multi-station of droughty and semiarid soil wind-erosion region and the effects of different windbreak porosity（β）,shelterbelt width,tree height and the angle between wind direction and shelterbelt on the movement and changes of wind speed were analyzed.【Result】Windbreak effect of sparse structure shelterbelt was the best,the highest value ran up to 34.27%,averaging 32.69%,and porous windbreak took second place,averaging 25.12% and ventilated windbreak was the worst,averaging 20.98%.When β was between 0.30-0.50,the windbreak effect of shelterbelts was the best,and the windbreak effect was better when there was difference between overstory layers and subtree layers.There was a positive correlation between wind direction and sinusoidal value of shelterbelt cut angle.When shelterbelt width was 2H-5H,the difference of windbreak effect of shelterbelts was little,when shelterbelt width was bigger than 5H,the windbreak effect of shelterbelts rapidly abated with the shelterbelt width addition.After airflow went into the network of forest area,the former four shelterbelts assumed subdued trend,subdued range of the first shelterbelt was the ultimate,and wind speed began to get back after going through the fourth shelterbelt.【Conclusion】Windbreak porosity of shelterbelt,width,height and wind direction were the main factors to determine the windbreak effect of single shelterbelt.