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

【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.