【作者】 刘芳；

【导师】 肖斌； 郝玉光；

【作者基本信息】 西北农林科技大学 ， 林业， 2008， 硕士

【摘要】 绿洲是乌兰布和沙漠最重要的生态经济区域,风沙危害严重地威胁着绿洲农田的健康运行,为保障绿洲农业的可持续发展,本文运用野外实验观测与室内分析相结合的方法,分别对绿洲植物防护体系各组成部分的防护效益进行了研究。其主要结果为:(1)将绿洲植物防护体系分为三层次,由外向内的次序是第一层以籽篙、沙鞭、白刺、沙冬青、沙蓬、沙介等低矮灌木为主的封沙育草带。第二层为人工栽植的防风阻沙带,以沙木蓼、柽柳、沙拐枣、梭梭、花棒、乌柳等大灌木构成。第三层以新疆杨、二白杨、沙枣为主要造林树种的农田防护林网。总体上,植物防护体系可以有效地减低风速,改变气流的搬运能力,阻挡风沙流和阻止流沙移动,从而有效地减轻绿洲的风沙危害。(2)封沙育草带内的天然植被白刺对风沙流有阻滞作用,使风沙流在沙丘的迎风坡受阻堆积,在背风坡风速下降可达39.2%～59.8%,并形成低速区,引起沙粒堆积。对不同植被盖度的沙丘输沙率研究表明;输沙率随风速的增加呈幂函数形式增加,随高度的增加呈指数规律递减,与流动沙丘相比,固定沙丘近地表0～10cm输沙量减少,10～40cm相对增加;从绝对输沙量变化分析,植被盖度大的固定沙丘、半固定沙丘输沙量相对于流动沙丘输沙量分别下降93.6%和59.8%;固定沙丘较半固定沙丘输沙量下降73.5%～90.5%。同时,封沙育带内天然植被防风作用效应也十分明显,可引起风速下降、沙粒沉积和输沙量减少,从而控制风沙流运动及流沙入侵。(3)人工营造的防风阻沙带对带内不同高度,特别是近地表20cm高度的风速均有降低作用,其主要是通过降低风速作用而减少了输沙能力,且对地表沙粒的控制功能与风速降低作用是相一致的,灌木林大于乔木林,枝丛密度大的灌木林优于枝丛密度小的灌木林。结果表明:通过营造合理配置的防风阻沙灌木林带可有效地将风沙拦截于绿洲之外。(4)绿洲农田防护林带在林前1H、林内、林后1H和林后7.5H处风速较林前7.5H处2m、1m、0.5m和0.2m风速均有不同程度的下降,且以近地表风速下降最大;新疆杨纯林的风速降低作用低于新疆杨与花棒混交林和沙枣纯林。绿洲防护林林内及林后输沙量下降比例大于林前,新疆杨与花棒混交林、沙枣林的输沙量小于新疆杨纯林。另外,选择以衡量防护林优劣的主要因子防风效能为指标,对当地最广泛采用的农田防护林网结构模式进行了深入研究,结果表明:两行一带式乔木防护林网的防风效能的大小主要决定于造林树种的冠形特征和密度,两行一带式新疆杨防护林网造林5年后,无叶期,开始具有初步的防风作用;8年生林网已具备较好的防风作用,无叶期防风效能可达45.7%;7年生两行式小乔木+沙枣1×1.5m的小间距林带,无叶期防风效能高达52.2%,已具备良好的防风作用。所以,选择较高密度的窄林带配置应采用窄冠型树种,否则难以得到预期的防护效益。同时,防风效能与林带间距具有一定影响,而与林带年龄和林带高度的关系不大。更多还原

【Abstract】 Oasis is the most important eco-economic area in Ulan Buh Desert.Wind-sand disaster is severely threatening the normal function of oasis farmland.To ensure the sustainable development of oasis agriculture,research on wind-sand disaster of oasis farmland and its control mechanism was carried out with methods of field test and laboratory experiment.The main research results are:(l)From outside to inside,Wind vegetation protective system in Ulan Buh desert is made up of three layers:sand-fixing grass belt,wind-sand prevention and fixing forest,and farmland shelterbelt.(2) Study on sand-trapping efficiency of sand-fixing grass belt show that the Nitraria tangutorum shrub on the fixed dune has the function of blocking wind-sand flow.Results show that the wind-sand flow is blocked in the slope.There is a slow down area on the windward of the fixed dune,wind speed is drop 39.2%-59.8%and sand is amassed there.The sand transport rate of the different dunes is increase along with the wind speed assumes the power function form,and decreasing with high increases assumes index rule.Research indicated:The shrub may fix the shifting dune,and blocked wind-sand flow.Analysis sand transport rate of the different dunes,we can see that the rate drops 93.6%separately in fixed dune and 59.8%in sedi-fixed dune;sand transport mass in fixed dune drops 73.5%-90.5% than that in sedi-fixed dune.The effect is obvious,so sand-fixing grass belt may drop wind speed and sand transport mass,make sand amass,that wind-sand flow is blocked and Wind-drift sand is stop inflowing.(3)Study on variation of sand transport mass about different dune in different velocity show,as the wind speed reduced,the sand transport mass is decrease,the function of blocking wind-sand flow is same as the wind speed dropping.Shrub forests have better effect than woody forest,shrubs with dense branches are better than those with sparse branches.In a word,the wind defending effect of shrub forests are obvious,it can effectively control farmland wind-sand disaster.(4) Wind velocity of different farmland shelterbelt was observed;results showed that defending farmland shelterbelt can make wind speed decreased,and Wind defending effect in sandy land is the best,and Pyramidalis Bunge is smaller than mixed forests with Pyramidalis Bunge and Hedysarum scaparium or Elaeagnus angustifolia forests.Moreover,shelterbelt can reduce the sand transport mass,and the fall rate in the forest and after the forest is more than the one before the forest.The sand transport mass of Pyramidalis Bunge is smaller than the one of mixed forests with Pyramidalis Bunge and Hedysarum scaparium or the one of Elaeagnus angustifolia forests.When we make farmland shelterbelt,we should afforest mixed forests,it can decrease the sand transport mass and increases stability of the structure.更多还原