防护林疏透度对近地层大气降尘的影响——以新疆策勒为例

Effect of Shelterbelt on Dust Deposition at Surface Layer:A case study in Cele,Xinjiang,China

防护林在削弱风速、减少风蚀的同时又可以影响近地层的大气降尘。为探讨防护林疏透度(β)对大气降尘的影响,对新疆杨防护林庇护区0.5m和3m高度降尘进行野外观测,并分析了两个高度降尘量空间分布。结果表明:β大于0.47时,防护林对降尘空间分布没有明显影响,0.5m高度降尘量大于3m高度,且林后3m高度降尘量比较平稳,而林后0.5m高度降尘量出现较大波动;β从0.47下降到0.2时,防护林可以明显影响林后降尘,两个高度降尘量变化趋势相似且平均降尘量差距减小;此段时间,林后两个高度均出现高降尘区,且0.5m高度的高降尘区滞后于3m高度。防护林在中等疏透度时(0.2~0.47)可以明显影响林后水平和垂直方向大气降尘,导致林后出现高降尘区,并促进3m高度降尘,减小两个高度降尘量的差距。因此,应避免将易受降尘危害的作物种植在林后高降尘区。

Shelterbelt had important effect not only on wind erosion but also on the dust deposition at surface layer.To identify the effect of shelterbelt with different porosity(β)on dust deposition,the dust samples at0.5 m and3 m height around Populus alba shelterbelt were collected.Results indicated thatβwas the key factor to control the dust deposition.Whenβ>0.47,the shelterbelt had no significant effect on dust deposition,and the deposition rates at 0.5 m height were higher than 3 m.The variation of deposition at 0.5 m height was considerable but relative steady at 3 m height.Whenβdecreased from0.47 to 0.2,the shelterbelt had significant effect on dust deposition,and the two heights had similar dust deposition pattern,and the deposition gap between two heights had decreased.Besides.There were high dustfall zones at the leeward of shelterbelt at both the two heights,but the high dustfall zone at 0.5 m height lagged behind the 3 m height.In conclusion,the shelterbelt with medium porosity(0.2-0.47)can affect the horizontal and vertical distribution of dust deposition,resulting in the leeward of shelterbelt had a high dust deposition zone.The shelterbelt can enhance the dust deposition at 3 m height to reduce the dustfall gap between0.5 m and 3 m.In view of the high dustfall zone at the leeward of the shelterbelt,the dust-vulnerable plants(e.g.cotton,winter wheat)should be planted far away from the near-leeward of the shelterbelt.