冀北坝上地区农田防护林防风固沙效应研究

Studies on Wind Break and Sand Fixation Effects of Farmland Shelterbelt in Bashang Area of Northern Hebei

以冀北坝上地区农田防护林为研究对象,通过野外观测风速和输沙量变化,对比分析乔木(杨树)、灌木(沙棘)、乔灌混交(榆树+柠条)3种不同类型防护林的防风固沙效应。结果表明,不同类型农田防护林水平方向上的防风效应差异显著,最大防风效应位置和防护范围不同;乔木防护林最大防风效应在林后2H(18 m)处,防护范围相对较大;灌木防护林最大防风效应在林后5H(12 m)处,乔灌混交防护林最大防风效应在林后3H(8 m)处,防护范围相对较小;总的来看,30、200 cm高度平均防风效应:灌木防护林(25.0%、20.8%)>乔灌混交防护林(24.2%、20.2%)>乔木防护林(15.9%、12.9%);垂直方向上的防风效应整体上呈现随着高度的增加而降低,30 cm高度防风效应优于200 cm高度。不同类型农田防护林能够降低风沙流高度,起到明显的固沙效应且差异显著;近地面0~60 cm高度输沙量随垂直高度的增加呈减小趋势,大部分集中在近地面0~20 cm内;总的来看,平均输沙通量乔木防护林(0.48 g·cm^-2·min^-1)>灌木防护林(0.36 g·cm^-2·min^-1)>乔灌混交防护林(0.35 g·cm^-2·min^-1);乔灌混交防护林和灌木防护林固沙效果优于乔木防护林。冀北坝上地区应综合考虑防风固沙效应和自然环境条件,积极探索与推广乔灌木混交、灌木为主的农田防护林建设。

Taking the farmland shelterbelts in the Bashang area of northern Hebei as the research objects,through the observation of wind speed and sediment in the field,three different types of shelterbelts of arbor(Populus),shrub(Hippophae rhamnoides)and mixed arbor and shrub(Ulmus pumila+Caragana korshinskii)were compared and analyzed.The results showed that the wind break effects of different types of farmland shelterbelts in the horizontal direction were significantly different,and the maximum wind break effect position and range were different.The maximum wind break effect of arbor shelterbelt was at 2H(18 m)behind the forest,and the range was relatively large;the maximum wind break effect of shrub shelterbelt was at 5H(12 m)behind the forest,and the maximum wind break effect of mixed arbor and shrub shelterbelt was at 3H(8 m)behind the forest,and the range was relatively small.In general,the average wind break effects in the heights of 30 and 200 cm were in the order of shrub shelterbelt(25.0%,20.8%)>mixed shelterbelt with arbor and shrub(24.2%,20.2%)>arbor shelter forest(15.9%,12.9%);the wind break effect in the vertical direction as a whole appeared to decrease as the height increased,and the wind break effect of 30 cm height was better than that of 200 cm height.Different types of farmland shelterbelts could reduce the height of sand flow,and played significant roles in sand fixation;with the increase of the vertical height,the sediment transport at the height of 0-60 cm decreased,and most of them were concentrated in the height of 0-20 cm.In general,the average sediment transport flux was arbor shelterbelt(0.48)>shrub shelterbelt(0.36)>mixed shelterbelt with arbor and shrub(0.35 g·cm^-2·min^-1);the sand fixation effects of shrub shelterbelt and the mixed shelterbelt with arbor and shrub were better than that of the arbor shelterbelt.Considering the wind break and sand fixation effects,as well as the natural environmental conditions comprehensively in Bashang,it was recommended that to construct farmland shelterbelts,tow patterns,mixed arbors and shrubs or shrubs should be emphasized.