【作者】 王翔宇；

【导师】 孙保平； 丁国栋；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2010， 博士

【摘要】 植被的防风蚀问题早已为学术界所关注,但过去的研究主要集中在植物覆盖度对土壤风蚀的影响方面,许多专家学者认为,较低的植被覆盖度不能完全固定流沙和阻止风沙流的形成。然而,在干旱、半干旱地区,由于水分条件的限制,植被的覆盖度不会很高。为达到防护效益最大并持续经营的目标,在保证林分多样性和稳定性的条件下,植被必须具有空间上布局的合理性和时间上的连续性。有必要对植被的配置结构进行研究,即通过合理配置,使植物在低覆盖度的情况下,既可减少水分的竞争,又达到防治土壤风蚀的效果。本文以毛乌素沙地常见植物种沙蒿为研究对象,通过对单株沙蒿周围流场的分布及输沙率的研究,分析其防治土壤风蚀机理。通过对不同盖度天然分布随机式沙蒿、不同盖度模拟均匀式沙蒿、不同水平配置行带式沙蒿的观测研究,对不同配置格局下风速、粗糙度、近地表输沙率等因子进行分析,从量化的角度探讨了不同水平配置格局沙蒿的防风阻沙效果及对土壤风蚀的防治机理。并通过风洞模拟实验,进一步分析了不同配置行带式沙蒿的防风效果。结果如下：(1)当风沙流流经单株沙蒿时,风速在其侧面表现出先增大后减少的趋势,在植株后形成减速区,背风面1H处风速减小程度最大,此后风速逐渐增大。风沙流在植株前后发生沉积,而在植株两侧发生轻微风蚀。单株沙蒿的防护距离在5-7H。天然灌草植被即是通过若干单一灌丛的集合效应而增强了其固沙机能,随着植被的生长从而逐渐控制了流沙运动。(2)通过对不同盖度天然随机式分布沙蒿样地的观测发现,在其他因素相同的情况下,随着植被盖度的增大,起沙风速呈指数函数增大,粗糙度和摩阻速率分别呈幂函数和线性函数增加。当地的警戒线盖度为41.5%-49.4%,土壤侵蚀的临界植被盖度为60%,即当天然随机式分布沙蒿盖度达到60%时,可基本控制地表风蚀。(3)控制地表风蚀方面,盖度50%是均匀式沙蒿的一个临界点。当均匀式分布沙蒿盖度在0-50%之间变化时,近地表风速逐渐降低,防风效能逐渐增强,地表粗糙度逐渐增大,近地表输沙率逐渐减小；当均匀式沙蒿盖度在50%-70%之间变化时,防风效能、地表粗糙度、近地表输沙率等并无显著不同。说明当均匀式沙蒿盖度达到50%时,可基本控制地表风蚀。(4)通过对不同行数人工模拟沙蒿灌丛观测发现：在一定范围内行数的增加增加了防护的范围,同时增强了各处的防护作用,对地表起到稳定的保护作用,但不是行数越多越好,三行配置防护效应较两行配置优势不明显,建议在实际设置中尽量选择两行的配置,两行配置的防护距离在7-10H。(5)同样为两行配置沙蒿灌丛,1H、2H、3H三种行距配置对1～7H段的防护效应差异不明显,均能较好的控制地表风蚀,降低风速；行距3H的配置能延缓7-12H段防护效应的衰减,但是行间部分地表会发生风蚀现象。实际营造中,应选用行距1H的配置,以防止行间出现风蚀。(6)对于两行一带的行带式配置沙蒿灌丛,带距4H、6H、8H、10H、12H配置下,带间的平均防风效能分别为61.2%、53.3%、45.4%、38.5%、29.2%,带间部分地表发生风蚀,随着带距的加大,风蚀地表面积加大,当带距加大到12H时,带间风蚀面积与堆积面积相当；带后阻沙效果明显,且随着距离的加大,阻沙效果逐渐减弱。4H、6H、8H、10H、12H带距的配置在带后7H处可分别降低输沙38.92%、35.24%、38.62%、39.69%、43.51%。(7)通过对不同行带式配置沙蒿进行风洞模拟实验观测,进一步验证了野外的结论。建议如下：在人工植被的建设中选用沙蒿时,应选择“两行一带”的多带式配置,考虑到沙区水分不足,沙蒿的带距应在8H-10H之间。此时防风阻沙效果较佳,又不至于过度消耗水分,引起沙蒿过早衰败死亡。更多还原

【Abstract】 The problem about preventing wind erosion of vegetation has long been concerned for academia, but the previous studies always focus on the effect that the vegetation coverage to soil drifting,many experts thought that when the vegetation coverage is low, it can’t completely fix shifting sand and prevent wind-sand flow.However, in arid and semi-arid region, because of the limit of water conditions, the vegetation coverage isn’t very high. To obtain maximum protection benefit and sustainable management objectives,on the condition of ensuring forest diversity and stability, vegetation must have reasonable space layout and continuity time。It is necessary to study forest configstruct and layout, namely,to appropriately ploy plants,it can reduce water competition and control soil erosion on low vegetation coverage. With the common plant Artemisia sphaerocephala as research subject, through the research on the wind field distribution and sediment transport rate, this paper analyzes the mechanism of preventing soil erosion;Through the studies of naturally random distributed Artemisia with different vegetation coverage, evenly distributed Artemisia that simulated with different vegetation coverage, zonal distributed Artemisia with different horizontal distribution,it analyzes wind speed, aerodynamic roughness, near-surface sediment transport rate on different vegetation coverage, and investigates the mechanism of sand-arresting effect and soil erosion control of Artemisia with different horizontal distribution;Through wind tunnel simulation experiment, it analyzes different zonal distributed Artemisia wind control effect. The results are as follows:(1) When wind-sand flow through an individual Artemisia plant,wind speed in the side of it will first increases and then decreases,it will form a wind shadow after the shrub,wind speed behind leeside 1H have the largest decrease,behind it,wind speed increase gradually. Wind-sand flow is deposited both in front and back of the plant, and it erode slightly in both sides of plant. Natural shrub grass vegetations were set several individual plant together to enhance the sand fixing function,and along with the growing of plant to control drift sand gradually.(2) Through the studies of naturally random distributed Artemisia with different vegetation coverage,it is discovered that with other things equal, when vegetation conversation increase, the threshold wind velocity of sand movement increases by exponential function, aerodynamic roughness and friction velocity respectively increases by power function and linear function. Warning coverage in study area is 41.5%-49.4%,critical coverage of soil corrosion is 60%,namely,when coverage of naturally random distributed Artemisia reaches 60%, soil drifting can be controlled basically.(3) The coverage of 50% was a critical point on preventing soil wind erosion.When coeverage degree changes in 0-50%,near-surface wind speed decreased, wind control effect strengthen, roughness increased and near-surface sediment transport rate decreased. When the coverage degree was more than 50% and less than 70%,the wind speed, wind control effect, roughness, near-surface sediment transport rate have no obvious difference. It suggestes that:when the coverage of evenly distributed Artemisia shrub reaches 50%, it can prevent soil wind erosion effectively.(4) Within a certain range, when linage numbers of shelter forest increasing, not only protect distance has been enlarged, but also protective effects has been enhanced that makes a stable protection to ground surface, but the number of rows is not the more the better. The protective effect of three rows allocation was not obvious better than two rows allocation. In practice, two rows allocation is suggested to choose,and its protect distance is 7-10H.(5) Three kind of 2 belts allocation that 1H,2H,3H have no obvious diffent on protect effect in the distance of 7-12H,all can control wind erosion effectively,and reduce wind speed; line spacing of 3H can suspend the attenuation of protection effect in 7-12H,but row middle will be eroded.(6) For one belt with two lines, wind control effect of 4H,6H,8H,10H,12H line spacing is 61.2%,53.3%,45.4%,38.5%,29.2%,surface between two lines is partly eroded.When line spacing increases, area eroded increases, when the spacing increases to 12H, wind erosion area is nearly equivalent to accumulation area; sand-arresting effect behind the belt is obvious,but with line spacing increasing, sand-arresting effect decreases.For 4H,6H,8H,10H,12H line spacing, sediment transport rate that 7H behind the belt decreases 38.92%,35.24%,38.62%,39.69%,43.51%.(7) Through the simulation experimental observation of different zonal distributed Artemisia wind control effect in wind tunnel,we test further the conclusion got in field.The suggestions are as follow:When Artemisia is as artificial vegetation,multi-belt distribution with each belt two lines should be chosed.Consider for the limit of water, the line spacing of Artemisia should be 8H-10H.In this distribution,sand-arresting effect is well, and water consumption will be not exceeding, that avert Artemisia died too earlier.更多还原