Study On Windbreak Effect And Spatial Distirbution Of Farmland Shelterbelts In Bashang, Hebei

For a long time, Bashang of Hebei Province suffers with strong wind which harms thecrop and leads to soil erosion frequently. Farmland shelterbelt Construction is an efficientmeasure to reduce wind speed and soil erosion. But Kangbao County is located inAgro-pastoral ecotone, northern of China, the cold and dry climate is not suitable for shelterforest., meanwhile, there are serious problems existing in the farmland shelter forest structureand tendency, which was constructed in “three north" shelterbelt program in the20centuryand the "Beijing-Tianjin sandstorm-control program" in recent years. A large number offarmland shelterbelts are destroyed due to the band management and operation. This articlestudies on windbreak efficiency and spatial distribution of different density of farmlandshelterbelts in Bashang of Hebei Province through the field observations and data processing,coming to the following conclusions, which provide a theoretical basis for farmlandshelterbelt Construction.(1) The land utilization of Kangbao County is not reasonable. Cultivated land is Oversize,forest and grassland growths year by year, but still with a low proportion. Kangbao Countyshould carry out the project of returning the farmland to forestland or grassland continually,expand the ecological land, strengthen the construction of farmland shelterbelt, to prevent andcontrol the soil erosion, and strive to achieve a ecological favorable pattern that cultivatedland decrease, but yield increase.(2) Arbor farmland shelterbelt, shrub farmland shelterbelt and arbor+shrub farmlandshelterbelt have a good windbreak effect. The wind will reduce in varying degree after goingthrough farmland shelterbelt, just due to the vary porosity; the windbreak efficiency will bedifferent.(3) In the horizontal direction, farmland shelterbelt with different porosity will hasdifferent windbreak efficiency in different distance. the maximum windbreak efficiency ofsparse farmland shelterbelt is32.08%, appearing at1H(H=average height of trees) behindfarmland shelterbelt; while windtight farmland shelterbelt is38%,at2H behind farmlandshelterbelt; and Ventilated is27.3%,at2H behind farmland shelterbelt，the wind speed will be low at2H-6H behind ventilated farmland shelterbelt, while as, windbreak efficiency is themaximum is this section, between21%-27.3%, and then the efficiency reduces gradually.(4) In the vertical direction, the windbreak efficiency of three porosity of arbor farmlandshelterbelt will decline gradually as the height increase in30cm,50cm100cm and200cm.But there will be wind speed fluctuation phenomenon in the four heights, which is mainlybecause of air was disturbed by shelterbelt when goes through it and the perturbance causedby the air form the top and go through the forest.(5)The total windbreak efficiency of different farmland shelterbelt: at the horizontalrange of1H-30H behind farmland shelterbelt: sparse farmland shelterbelt is20%; Windtightfarmland shelterbelt is18%; Ventilated farmland shelterbelt is15%.At the horizontal range of1H-20H behind farmland shelterbelt: the average windbreakeffect of arbor+shrub farmland shelterbelt is28.60%; medlar shrub is22.32%. Therefore,evaluating within1H~30H the average windbreak efficiency: sparse> windtight> ventilated;within1H~20H: elm+shrub> shrub...