水保所知识产出(1956---)知识库

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 265.0
mm，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。
关键词：退耕还林；土壤水消耗；尺度；林下植被；疏伐

In recent years, the dramatic changes in vegetation has been made by large-scale
farmland to forest on the Loess Plateau of China. However, the negative feedback
between vegetation growth and soil water capacity has been developed due to
irrational vegetation construction, which makes the formation of dried soil layers
(DSL), the emergence of vegetation degradation and other ecological problems.
Meanwhile, warming-drying trend exacerbated the contradiction between water use of
forest and soil water supply, and caused safe supply of water resources in the region.
To use the limited-water resources maintaining the sustainable development of
artificial forest ecosystem on the Loess Plateau becomes an important goal of
ecological environment construction in the region, and the core of the goal is soil
water. Therefore, studying soil water effects of returning farmland to forest on the
Loess Plateau of China, it is helpful to study the mechanism of soil-water
conservation of artificial forest ecosystem in theory, and it is of great practical
significance for the limited-water resources utilization and the management of forest
in practice.
In this paper, the soil water content (SWC) of 0 ~ 5.0 m soil layer was studied for
the artificial forest on the Loess Plateau at large scale. The factors affecting the
distribution of soil water in different soil layers were quantitatively analyzed. The
characteristics of DSL and its influencing factors were analyzed along the transect
scale. The characteristics and influencing factors of soil water storage (SWS) for
understory vegetation and understory vegetation removal were dynamically monitored
and analyzed at plot scale. Based on the analysis of the change of SWC in the process  of redistribution of overstory (refer to the net input of soil water without canopy
intercept), surface runoff and changes in SWS in the growing season, the
characteristics of understory evapotranspiration (E u ) and its influencing factors were
studied according to the principle of water balance. At the same time, the soil water
balance of artificial forest ecosystem was studied under different thinning treatments.
The main conclusions are as follows:
1. Evaluation of soil water effects of returning cropland to forest on the Loess
Plateau. SWC in artificial forest is generally lower than the agricultural land, SWS
decreased by an average of 169.6 mm. The SWS capacity of 3.0 ~ 4.0 and 4.0 ~ 5.0 m
soil layer is larger than 1.0 ~ 2.0, 2.0 ~ 3.0 m soil layer, and the losses of soil water
increases with the depth of soil layer. SWS in different rainfall areas is different.
Rainfall in the area of > 550 mm, the highest loss of soil water is 214.7 mm, the loss
of soil water in the area of 450-550 mm is 195.7 mm, and in the area <450 mm is the
least, only 36.0 mm. There was a significant positive correlation between soil water
losses and initial SWS, rainfall, temperature and slope.
2. Evaluating the dominant factors affecting the spatial pattern of soil water in
different soil layers. SWC has great variation in different types of artificial forest
different. The results showed economic forest (ENF)> ecological forest (ELF)> shrub
land (SL), variability of deep SWC was great. Rainfall and clay content had the
greatest influence on soil water distribution in different soil layers. With the increase
of soil depth, the local factors had a great influence on the soil water distribution of
ELF, while the meteorological factors had a great influence on the soil water
distribution of ENF, but there was no significant difference between the local
influence and the meteorological factors for SL.
3. Spatial pattern and influencing factors of DSL along a south-north transect
scale. SWC gradually reduced in the vertical direction, soil desiccation serious. The
average thickness of DSL was 289.1 cm, the average water content of DSL was 7.7%,
and the formed depth of DSL was 151.9 cm. There was a large variation of DSL in
different rainfall areas. From dry area to arid area, SWC in DSL decreased and then
increased. The contribution of environmental factors explained variability to DSL  variation was 38.0%. Local factors alone explained the percentage of variability
(16.5%) was greater than the climatic factors alone (4.2%).
4. Soil water effects of returning cropland to forest at hill-slope scale. The more
distance to the gully, the greater SWS. The soil sampling site at distance of 300 cm
could represent the average of the SWS at the measured scale. In the vertical direction,
SWC had a great variability, which controlled by gully. Under the different vegetation
types, spatial distribution pattern of SWC was dominated by vegetation types, gully,
however, slope position, micro-terrain and other factors had a lesser influence.
5. The effects of undergrowth vegetation on soil water balance in artificial forest
on the Loess Plateau. In the artificial forest of Robinia pseudoacacia, the percentage
of throughfall accounted for about 87.3% of the rainfall outside the forest,
interception by the canopy was followed, which accounted for about 10.4% of the
rainfall, the percentage of stemflow accounted for about 2.3% of the rainfall. During
the observation period, water use of E o was about 265.0 mm, the water use of E u was
about 120.5 mm, and the percentage of the E u was about 31.3% accounted for the
water use of whole forest during the growing season.
6. The effect of ecological thinning on soil water balance in artificial forest.
During the observation period, soil water deficit were 82.4 mm and 38.5 mm for
thinning 40% and 90%, respectively. Soil water deficit was less with increased
thinning. With the increasing of the thinning for artificial forest, the transpiration of
understory vegetation increased by 52.5 mm. The increased in transpiration of
understory vegetation offset the increased part of evapotranspiration of the thinning.
In summary, extensive afforestation on the Chinese Loess Plateau has led to
decreases in deep SWC, and formed a persistent DSL due to soil water deficit, which
has a profound effect on the artificial forest ecosystem, while the E u couldn‘t be
neglected, which is a great water loss part of artificial forest ecosystem. The
ecological thinning for artificial forest can significantly change soil hydrological cycle
process.
Key words: Afforestation, Soil water loss, Scale, Understory vegetation, Thinning,
Loess Plateau