黄土高原退耕还林的土壤水分效应研究

发布时间：2018-02-27 19:46

本文关键词： 退耕还林土壤水消耗尺度林下植被疏伐　出处：《中国科学院教育部水土保持与生态环境研究中心》2017年博士论文　论文类型：学位论文

【摘要】：近年来黄土高原大规模的退耕还林使得该区成为我国植被变化最剧烈的地区。然而,造林后土壤水分供给负反馈导致土壤干层在黄土高原广泛出现。同时气候暖干化更加剧了森林需水与土壤供水之间的矛盾,危及区域水资源供给安全。如何利用有限水资源维持黄土高原人工林生态系统持续发展是目前该区生态建设的重要目标,而其核心就是土壤水分。因此,研究退耕还林的土壤水分效应,在理论上有助于揭示人工林生态系统水源涵养机理,在实践上对于该区有限水资源利用,以及对人工林管理具有重要的现实意义。本论文以黄土高原人工林生态系统为研究对象,对人工林0~5.0 m土层的土壤水分进行了大面积调查研究,定量分析了不同土层影响土壤水分分布及主要因素,研究了南北样带土壤干燥化效应及影响因素,动态监测并分析了林下植被和去除林下植被小区尺度土壤储水量的变化特征及其影响因素,通过分析小区尺度上层林木降水再分配过程土壤水分净输入(指除去冠层截留净输入土壤的水分)、地表径流和生长期剖面土壤储水量变化的基础上,根据水量平衡原理对林下植被的蒸散耗水特征及其影响因素进行了研究,同时结合生态疏伐管理研究了不同疏伐处理下人工林土壤水分平衡,所取得主要结论如下:1.评估黄土高原退耕还林的土壤水分效应。人工林土壤含水量普遍低于农地,土壤储水量平均减少169.6 mm。3.0~4.0和4.0~5.0m土层土壤储水量比1.0~2.0、2.0~3.0 m浅土层要损失量最大,土壤储水量消耗随着土层深度增加而增加。不同降雨区土壤储水量消耗不同。降雨量550mm区域,土壤储水量损失的最高,为214.7 mm,450~550 mm区域土壤储水量损失195.7mm,450 mm区域土壤储水量减少的最少,仅为36.0 mm。土壤水分消耗与退耕前土壤水分、降雨量、气温和坡度呈显著正相关。2.评估不同土层土壤水分空间格局的主导因素。不同类型人工林地土壤水分分布不同。土壤含水量表现为经济林生态林灌木,深层土壤水分变异性较大。降雨量和粘粒含量对不同土层土壤水分分布格局影响最大。随着土层深度增加,局地因素对生态林土壤水分影响较大,气象因素对经济林土壤水分影响较大,而在灌木地局地影响和气象因素差异不大。3.南北样带土壤干燥化效应及影响因素。在垂直方向上,剖面土壤含水量逐渐减小,土壤水分亏缺严重,形成土壤干层。土壤干层平均厚度为289.1 cm,干层平均含水量为7.7%,干层起始平均深度为151.9 cm。不同降雨区土壤干层有较大的变异性,由湿润区到干旱区,土壤干层水分先减小后增加。环境因子解释的变异性对土壤干层总变异性的比例为38.0%。局地因素单独解释变异性比例(16.5%)大于气候因素单独解释的变异性比例(4.2%)4.坡面尺度退耕还林的土壤水分效应。距边坡越远土壤储水量愈高,300 cm处样点可代表测定尺度下土壤储水量的平均值。在垂直方向上,边坡增大了土壤水分的变异性。不同植被类型下,土壤水分空间分布格局受植被类型主导,沟道、坡位、微地形等因素处于次要地位。5.黄土区人工林林下植被对土壤水平衡的影响。人工刺槐林地,穿透雨占林外降雨量比例约87.3%,其次为冠层截留占林外降雨量比例约为10.4%,茎干流最小约占林外降雨量比例的2.3%。观测期内上层林木蒸腾耗水量约为265.0mm,林下植被蒸散耗水量约为120.5 mm,林下植被蒸散耗水量约占生长期森林耗水量的31.3%。6.生态疏伐对人工林土壤水平衡的影响。整个观测期内,疏伐40%和90%处理土壤水分分别亏缺82.4 mm和38.5 mm。随疏伐程度增加土壤水分消耗减小。同时随着疏伐增加到90%时,林下植被蒸腾耗水增加52.5 mm。林下植被蒸腾的增加抵消了疏伐林分的水分蒸腾部分。综上所述,黄土高原大规模退耕还林消耗了深层土壤水分,土壤水分严重亏缺形成持久的土壤干层,对区域人工林生态系统产生深刻影响,同时林下植被蒸散耗水是人工林生态系统不可忽视的水分耗损项,对该区进行生态疏伐可以显著改变土壤水分循环过程。
[Abstract]:In recent years, large-scale farmland in the loess plateau forest makes the area has become the area of vegetation in China the most dramatic changes. However, after afforestation, soil water supply leads to negative feedback of dried soil layer in the Loess Plateau appeared widely. At the same time, climate warming has intensified the contradiction of forest water and soil water supply between the endanger of regional water resources supply security. How to use the limited water resources in forest ecosystems of the Loess Plateau is the important goal of maintaining the sustainable development of the ecological construction in this area, and its core is the soil moisture. Therefore, study on the effect of returning farmland to forest soil moisture, helps to reveal the mechanism of water conservation plantation ecosystem in theory and in practice for the use of limited water resources, and has important practical significance for plantation management. In this paper, the Loess Plateau artificial forest ecosystem as the research object, the 0~5.0 m plantation soil layer The soil moisture was investigated in large area, the quantitative analysis and the main factors influence the distribution of soil moisture in different soil layers, the factors in NSTEC soil desiccation and influencing factors are analyzed, the dynamic monitoring of forest vegetation and removal of understory vegetation soil storage water district scale change characteristic and its influence, through the analysis of community the upper scale forest rainfall redistribution of soil water net input (refers to the removal of canopy interception net input soil moisture), basic profile of surface runoff and soil water storage period of growth, according to the water balance principle of evapotranspiration under forest vegetation water consumption characteristics and its influencing factors were studied, combined with ecological thinning management research the different thinning treatments of soil under artificial forest water balance, the main conclusions are as follows: 1. to evaluate the effect of soil moisture in the Loess Plateau is artificial forest. Forest soil moisture is lower than that of farmland, reduce the average soil water storage of 169.6 mm.3.0~4.0 and 4.0~5.0m soil water storage capacity than 1.0~2.0,2.0~3.0 m in shallow soil loss to the largest amount of soil water consumption increased with the increase of soil depth. The soil water of different water consumption of different rainfall area. Rainfall area of 550mm, the highest soil water loss, 214.7 mm 450~550 mm, regional soil water loss 195.7mm, reducing 450 mm soil storage area water at least, only 36 mm. soil water consumption and before returning farmland to soil moisture, rainfall, and temperature gradient was positively related to.2. evaluation factors of soil moisture in different soil spatial pattern. Different types of artificial forest soil water distribution is different. Soil moisture is economic forest shrub forest, deep soil moisture variability of rainfall. And the clay content of different soil layer Effect of water distribution pattern. With the increase of soil depth, local factors have great influence on forest soil moisture and meteorological factors have great influence on the economic forest soil moisture, and the influence factors in the shrub and local meteorological factors had little difference.3. NSTEC soil desiccation and influence. In the vertical direction, the soil water content decreased gradually soil water deficit, serious, the formation of dry soil layer. The soil dry layer thickness is 289.1 cm, the dry layer average moisture content is 7.7%, the average depth of soil dry layer initial 151.9 cm. different rainfall area dry layer variability is large, the humid to arid area, dry layer of soil moisture decreased first and then increased the proportion of variability. Environmental factors explain the total variability of soil dry layer for 38.0%. local factors alone explain the variability of the proportion (16.5%) proportion of climate variability than single factor explanation (4.2%) 4. slope The surface scale effect of soil moisture in returning farmland to forests. The farther from the slope of soil water is higher, 300 cm samples can represent the determination of average soil water storage scale value. In the vertical direction, the slope increases. The variation of soil moisture under different vegetation types, soil moisture spatial distribution pattern of vegetation the dominant type, channel, slope position, micro topography and other factors in the influence of the secondary position of artificial forest in loess area.5. under vegetation on soil water balance. Robinia pseudoacacia plantation, throughfall percentage of rainfall outside the forest was about 87.3%, followed by the rainfall outside the forest canopy interception accounted for about 10.4% of the 2.3%. observation period of minimum stem Yuezhanlin rainfall ratio in the upper layer of transpiration water consumption is about 265.0mm, the understory vegetation transpiration is about 120.5 mm, understory vegetation evapotranspiration accounted for about 31.3%.6. of ecological water consumption of forest thinning during the growth period of cutting on Plantation Soil Effect of soil water balance. The whole observation period, thinning 40% and 90% soil moisture deficit were 82.4 mm and 38.5 mm. with thinning increased soil water consumption decreased. At the same time as the thinning increased to 90%, the understory vegetation transpiration water consumption increased 52.5 mm. understory vegetation transpiration increase offset by transpiration part of the thinning stands. In summary, the Loess Plateau large-scale farmland to forest consumption of deep soil moisture, soil moisture deficit form lasting dried soil layer, have a profound impact on the regional plantation ecosystem, and understory vegetation evapotranspiration is artificial forest ecosystem water loss can not be ignored, in this area ecological thinning can significantly change the soil water cycle process.

【学位授予单位】：中国科学院教育部水土保持与生态环境研究中心
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S714

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