【作者】 郝玉光；

【导师】 吴斌；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2007， 博士

【摘要】 乌兰布和沙漠东北部的磴口人工绿洲历史悠久,新中国成立后,国家投入大量人力、物力,经历多次大规模沙荒土地的整治与开发,建成了大面积的人工灌溉绿洲,区域生态环境发生了深刻的变化。研究该人工绿洲系统的生态效应及其动态变化,对维护绿洲的可持续发展提供科学依据具有重要的现实意义。本文以人工绿洲的生态效应为切入点,采用点面结合的方法,以磴口县区域生态环境为面,以沙漠林业实验中心实验场新建人工绿洲为点,通过野外调查和室内测试相结合、定位观测与半定位观测相结合的方法,并运用3S技术,对人工绿洲生态效应系统进行的多层次及不同空间、时间尺度分析和研究,初步结果如下:(1)新中国成立后,磴口县沙荒土地经历了多次的大规模绿洲开发建设,在长期大规模的人工绿洲化过程中,由于资源的不合理利用,产生了一系列的生态问题。近年来(1990年和2003年),磴口县绿洲化与荒漠化相关景观格局的相互转化明显。研究表明:磴口县区域生态环境仍处在局部改善,整体恶化之中。流动沙地的面积显著增加,对绿洲最具生态保护功能的覆盖度高的天然灌丛植被—固定沙地面积显著减少,人工绿洲的扩展主要建立在破坏自己天然保护屏障的基础之上,这种潜在的生态危机,将会给人工绿洲的持续发展带来威胁。(2)不论绿洲内部,绿洲边缘、还是绿洲外围,在区域干旱气候的共同背景下,由于受人工绿洲灌溉水分水平运动影响强度的不同,其植被的组成种类、盖度及多样性特征存在着比较大的差异,因而造成其生态功能的显著差别。绿洲外缘天然灌草及人工植被由于其结构差异,造成地表粗糙度明显不同,其防蚀、阻沙、固沙作用也有明显的差别。流动沙地表现为强风蚀、强堆积,而高盖度天然灌丛植被区表现弱风蚀、弱堆积特点。从绿洲边缘向远处沙漠的水平梯度上,不同下垫面的沙尘沉降量差异显著,随着植被盖度的增大,沙尘沉降量显著减少,并且,同一下垫面的垂直梯度上沙尘沉降量的差异也十分显著。(3)对绿洲典型研究区人工绿洲幼龄林后期、中龄林、成熟林3个阶段的小气候效应的研究表明(与荒漠相比):生长季绿洲降低气温和地表温度的作用明显;增加降水的作用显著,3个阶段降水增长率分别为8.3%、20.3%、67.1%;提高空气湿度,3个阶段分别提高4.5%、4.7%、2.7%,作物生长季节,绿洲内比荒漠提高约6～9%;抑制蒸发作用明显,3个阶段从人工绿洲的蒸发量分别减少为24.4%、32.2%、12.7%,最热月7月降幅最大,为40.2%;降低风速明显,3个阶段的防风效能分别为41.5%、47.2%、37.1%。人工绿洲成熟林阶段,除年降水量有明显增加外,其它多项小气候因子的变化幅度减小,特别是人工绿洲成熟龄林阶段在非生长季的防风效能高于幼龄林后期阶段,而在生长季的防风效能正好相反的现象,正好说明人工绿洲的防风效应完全决定于其防护林,其防风作用的减弱,表明进入成熟期后,生态功能呈下降趋势,可作为防护林更新的理论依据。人工绿洲在24年的绿洲化进程中(1980～2004年),绿洲土壤质量得到明显改善,土壤的全量养分、速效养分总体上都呈增加趋势,表层土壤含盐量和PH值均下降明显,土壤质量的改善,为人工绿洲农业产业高产稳产及持续经营奠定了基础。(4)通过对不同时间序列多种结构林带(网)无叶期防风作用的系统的研究,农田防护林防风效能,主要决定于林带结构。单一树种的防护林带,防风效能主要决定于主林带间距、树种的冠型特征和造林密度,两树种混交林带,防风效能关键决定于树种搭配,对此在防护林设计上应予以高度重视。林带的防风效能与其宽度关系不大,为窄林带设计提供了依据。干旱沙区人工绿洲营建农田防护林具有稳产高产的作用,与无林网保护的农田相比增产作用显著,增产率在25.0%～155.7%,且在防护林网内农作物的质量性状也有改善。结构合理的农田林网其自身的增产作用大于胁地作用,以玉米为例,林网自身对农作物的实际增产率为3.6%。二白杨农田防护林23a时,立木材积增长和防风效能同时进入显著下降阶段,说明此期的二白杨防护林进入了成熟期,可作为采伐更新的年龄,年龄为23a。(5)区域防护林体系建设能有效抑制和减弱风沙天气,随着“三北”防护林工程建设,抑制风沙天气形成的作用趋势显著提高。1970年至2000年,磴口县年均大风日数、扬沙日数和沙尘暴日数总体上呈明显的下降趋势,在不同建设阶段各指标均明显下降,尤其是第3阶段,风沙天气各指标下降幅度可达73.0～94.0%。风沙天气指标(年均大风日数、扬沙日数和沙尘暴日数)与防护林体系的面积和蓄积量有显著的负相关关系。人工绿洲典型研究区监测研究表明,防护林体系对灾害性天气具有明显的降减作用与区域防护林体系的作用结果相一致。同时,防护林体系可有效地降减沙尘天气,使得绿洲内降尘量减少,沙尘天气的程度和强度有所缓解。更多还原

【Abstract】 The artificial oasis of Dengkou, in the northeast of Ulan Buh Desert, has a long reclamation history. Since the founding of New China, the governments has plough into a large amount of manpower and materials for management and exploitation of sandy wastelands, a large-scale irrigated oasis has been established, leading to the great change of local eco-environment. Studies on ecological effects and dynamic changes of the artificial oasis are of great realistic significance to maintain the sustainable development of the oasis.Taking the ecological effects of artificial oasis system as starting point, serving the prevention and control of sand blown disaster, using an integrated method that combined positioning experiments, regional survey and laboratory analysis, the ecological functions of oasis system, that consist of the peripheral natural desert vegetation, in sight of sand-fix shrubs, as well as wind-break forest and farmland within oasis etc., were studied in different spatial scales, and the preliminary results of study were achieved as follows :(1) Since the founding of New China, the sandy wasteland in Dengkou Oasis has experienced several large-scale reclamations. Because of the expansion of oasis and the immoderate utilization of water resources, a series ecological problem has occurred. From 1996 to 2003, the landscape pattern of Dengkou region, related to the oasis-making and desertification, has changed significantly. The study indicates that ecological condition in Dengkou region is still deteriorated on the whole although improved partially. The area of shifting sands increased largely, and the area of natural shrub vegetation decreased simultaneously. The expansion of artificial oasis directly lead to the destruction of their natural vegetation that oasis is protected from sand blown. The potential ecological crisis is threatening the sustainable development of artificial oasis.(2) The study showed that the vegetation species composition, coverage and diversity evidently differed from each other, accordingly resulted in notable difference of their ecological function under the common background of regional arid climate whether in the Oasis and on the edge of oasis or in theperiphery of oasis, as different influencing intensity of irrigation water horizontal movement of artificial oasis. The structural difference of natural shrub and herbage and artificial vegetation cause significantly different surface roughness, consequently anti-erosion,sand blocking and sand fixing also has a marked difference. Mobile sandy land characterizes as strong wind erosion, strong deposition while natural shrub vegetation area with high coverage characterizes as weak wind erosion and weak deposition. The depositing quantity of different underlying surfaces at different levels gradients varies range from the edge of the oasis to distant desert .With vegetation coverage increasing, the dust depositing quantity significantly reduced, while the dust depositing quantity of the same underlying surface at different height changes significantly, the dust depositing quantity at 0.5m is significantly greater than that at 1.5m.(3) The research on climate ecological effects of typical artificial oasis in 3 stage of from young-late age plantation and middle-age plantation to near-maturation plantation middle age shows that (compared with the desert) : artificial Oasis can reduce air temperature and surface temperature; artificial Oasis can increase precipitation and the growth rate of precipitation of three stages were 8.3%,20.3%,67.1%; artificial Oasis can improve air humidity which respectively increases by 4.5%,4.8%,3.7%. The air humidity in oasis is higher about 6-9% than that in desert during growing season.; artificial Oasis can efficiently restrain evaporation, and the rate of evaporation fell by 40.2% in July — the hottest month of the year; artificial Oasis can reduce the speed of wind, the wind protective effect of the three phases respectively is 41.5%,47.2%,37.1%. The ecological function of a number of climatic factors decline obviously from 2003 to 2005 in artificial oasis, which indicates the mature stage of shelter-forest seems to be the appropriate updating age of farmland shelterbelts.In the process of Oasis development last over 20 years, soil quality of newly constructed artificial oasis had been remarkably improved, the total soil nutrients and available soil nutrient increased on the whole while the salt content and the PH value in the top layer of soil surface decreased significantly. The improvement of soil quality laid foundation for highly stable yielding and sustainable management of oasis agricultural industry.(4) Major disaster of artificial oasis is Sand drift in the North- East of the Ulan Buh Desert Area and farmland shelterbelts is primarily looked forward to reducing the wind speed. Study on shelterbelts (networks) with different structure and a variety of time sequence and without leaf shielding effectshows that spacing distribution for shelterbelt is the key factor to the wind protective effect of farmland shelterbelts. The wind protective effect of monospecies shelterbelts is mainly due to spacing distribution for prior shelter belt, canopy features and planting density while the shelterbelt mixed two species mainly due to combination between kinds of trees , which must be highly valued. The wind protective effect of Shelterbelt has little to do with the width, which has great significance.The shelter forest in arid desert can ensure high and stable yield of farmland , and the growth rate is between 5.0%～155.71% ; The quality and properties also improve clearly with protective forest. Shelter forest with rational structure has less effect on yield of farmland. Taking corn as example, the crop yield increase rate by shelter forest is up to 3.6%.The increase of timber volume of Alamo shelter forest(23a) is descending, while function for wind break became poor, which indicates that Alamo shelter forest is come into mature stage and should be renewal.(5) Along with implementation of the "Three North" shelter forest project, regional shelter systems can effectively restrained and weakened sandstorm. The annual average of wind days blowing sand and dust storm days totally decline from 1970 to 2000. Every index descends markedly , especially in the third stage it fell by 73.0～ 94.0%, which indicates the indices (average number of days of strong wind, blowing sand and dust storm days )is linearly related to the area and timber volume of regional shelter system .Monitoring typical artificial oasis shows that shelter system can decrease significantly the harm of disastrous weather, which accords with regional shelterbelt systems. Simultaneously, shelterblet systems can efficiently reduced sand-dust, yield at certain extent.更多还原