Attribution analysis based on Budyko hypothesis for land evapotranspiration change in the Loess Plateau,China

Land evapotranspiration (ET) is an important process connecting soil, vegetation and the atmosphere, especially in regions that experience shortage in precipitation. Since 1999, the implementation of a large-scale vegetation restoration project has significantly improved the ecological environment of the Loess Plateau in China. However, the quantitative assessment of the contribution of vegetation restoration projects to long-term ET is still in its infancy. In this study, we investigated changes in land ET and associated driving factors from 1982to 2014 in the Loess Plateau using Budyko-based partial differential methods. Overall, annual ET slightly increased by 0.28 mm/a and there were no large fluctuations after project implementation. An attribution analysis showed that precipitation was the driving factor of inter-annual variability of land ET throughout the study period; the average impacts of precipitation, potential evapotranspiration, and vegetation restoration on ET change were 61.5%, 11.5% and 26.9%, respectively. These results provide an improved understanding of the relationship between vegetation condition change and climate variation on terrestrial ET in the study area and can support future decision-making regarding water resource availability.     

Soil hydraulic conductivity as affected by vegetation restoration age on the Loess Plateau,China

The Loess Plateau of China has experienced extensive vegetation restoration in the past several decades,which leads to great changes in soil properties such as soil bulk,porosity,and organic matter with the vegetation restoration age.And these soil properties have great effect on the soil infiltration and soil hydraulic conductivity.However,the potential changes in soil hydraulic conductivity caused by vegetation restoration age have not been well understood.This study was conducted to investigate the changes in soil hydraulic conductivity under five grasslands with different vegetation restoration ages(3,10,18,28 and 37 years)compared to a slope farmland,and further to identify the factors responsible for these changes on the Loess Plateau of China.At each site,accumulative infiltration amount and soil hydraulic conductivity were determined using a disc permeameter with a water supply pressure of –20 mm.Soil properties were measured for analyzing their potential factors influencing soil hydraulic conductivity.The results showed that the soil bulk had no significant changes over the initial 20 years of restoration(P0.05);the total porosity,capillary porosity and field capacity decreased significantly in the grass land with 28 and 37 restoration ages compared to the slope farmland;accumulative infiltration amount and soil hydraulic conductivity were significantly enhanced after 18 years of vegetation restoration.However,accumulative infiltration amount and soil hydraulic conductivity fluctuated over the initial 10 years of restoration.The increase in soil hydraulic conductivity with vegetation restoration was closely related to the changes in soil texture and structure.Soil sand and clay contents were the most influential factors on soil hydraulic conductivity,followed by bulk density,soil porosity,root density and crust thickness.The Pearson correlation coefficients indicated that the soil hydraulic conductivity was affected by multiply factors.These results are helpful to understand the changes in hydrological and erosion processes response to vegetation succession on the Loess Plateau.     

红砂植被盖度对土壤不同形态碳、氮及细菌多样性的影响

以自然恢复的红砂群落为研究对象,探讨黄土高原红砂植被不同盖度对土壤不同形态碳、氮及细菌多样性的影响,为该地区的人工生态恢复措施提供理论支撑.在兰州市南北两山植被恢复技术研究与示范基地,按照5级盖度分类法设置红砂植被盖度梯度,重点对土壤养分碳氮、微生物量碳氮和细菌多样性开展研究.结果表明:随着植被恢复,土壤有机碳 (SOC)和全氮(TN)、土壤微生物碳 (MBC)和微生物氮(MBN)逐渐提高,并且增加比较快 ,但是当总盖度达到48.73%之后,增加比较缓慢,而且增加的差异不显著.相同的植被盖度对土壤有机碳、全氮和土壤微生物碳、氮的影响趋于一致.土壤细菌多样性随植被盖度有所增加,在植被盖度达到48.73%后多样性维持在彼此接近的水平,尽管微生物多样性群落结构有差异 .在植被稀疏、物种多样性较低的干旱坡地,红砂植被盖度增加明显改善了土壤生态功能, 但是片面追求植被盖度的增加,对土壤特性改善有限.     

Land cover change and eco-environmental quality response of different geomorphic units on the Chinese Loess Plateau

Land cover in the Chinese Loess Plateau has undergone dramatic changes since the late 1980s.Revealing the trend in land cover change and eco-environmental quality response of different geomorphic units in this stage is a realistic requirement for promoting sustainable development of the Chinese Loess Plateau.Based on the data of geomorphic units and land cover in 1990,2000,2010 and 2018 of the Chinese Loess Plateau,we studied the trend of land cover change and eco-environmental quality response of different geomorphic units by using a significance index of land cover change,a proportion index of land cover change and an eco-environmental response model.The results indicated that from 1990 to 2018,the areas of forestland and construction land substantially increased,whereas those of cropland,grassland,wetland and unused land considerably decreased.Land cover change exhibited large geomorphic differences,and the main conversion of land cover was from cropland into other land types.Unstable trend of land cover change in the loess tablelands and sandy loess hills declined,whereas the unstable trends in the other geomorphic units enhanced.Eco-environmental quality varied among different geomorphic units.The expansion of construction land and degradation of forestland,grassland and wetland resulted in the deterioration of eco-environmental quality.The conversion of cropland and unused land into forestland and grassland,and the conversion of grassland into forestland were the main factors that drove the improvement of eco-environmental quality.The findings of this study may provide theoretical reference and support decision making for the optimization of land use structure and the improvement of eco-environmental quality on the Chinese Loess Plateau.     

Dynamics of ecosystem carbon stocks during vegetation restoration on the Loess Plateau of China

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil(0–100 cm), plant biomass and the ecosystem(plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation(natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0–100 cm. Moreover, there was a time lag of about 15–30 years between biomass production and soil carbon sequestration in 0–100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.     

Changes in diversity,composition and assembly processes of soil microbial communities during Robinia pseudoacacia L. restoration on the Loess Plateau,China

Robinia pseudoacacia L. (RP) restoration has increased vegetation cover in semi-arid regions on the Loess Plateau of China, but ecological problems have also occurred due to RP restoration, such as reduced soil moisture. Further, it is still uncertain how microbial diversity, composition and assembly processes change with RP restoration in semi-arid regions. Therefore, amplicon sequencing of small subunit ribosomal ribonucleic acid (16S rRNA) and internal transcribed spacer (ITS) genes was performed to study soil bacterial and fungal diversity, composition and assembly processes at four study sites with different stand ages of RP plantations (Y10, RP plantation with stand ages less than 10 a; Y15, RP plantation with stand ages approximately 15 a; Y25, RP plantation with stand ages approximately 25 a; and Y40, RP plantation with stand ages approximately 40 a) along a 40-a chronosequence on the Loess Plateau. The diversity of soil bacteria and fungi increased significantly during the restoration period from 10 to 15 a (P<0.05). However, compared with Y15, bacterial diversity was lower at Y25 and Y40, and fungal diversity remained stable during the restoration period between 25 and 40 a. The relative abundances of Proteobacteria and Ascomycota increased during the restoration period from 10 to 15 a. Conversely, after 15 a of restoration, they both decreased, whereas the relative abundances of Actinomycetes, Acidobacteria and Basidiomycota gradually increased. The variations in soil bacterial communities were mainly related to changes in soil total nitrogen, nitrate nitrogen and moisture contents, while soil fungal communities were mainly shaped by soil organic carbon and nitrate nitrogen contents. Bacterial communities were structured by the heterogeneous selection and stochastic process, while fungal communities were structured primarily by the stochastic process. The RP restoration induced an increase in the relative importance of heterogeneous selection on bacterial communities. Overall, this study reveals the changes in microbial diversity, community composition and assembly processes with RP restoration on the Loess Plateau and provides a new perspective on the effects of vegetation restoration on soil microbial communities in semi-arid regions.     

关于黄土高原退耕还林(草)问题

论述了退耕还林 (草 )是黄土高原水土保持、生态环境建设中一项战略性措施 ,分析了在满足农村人口粮食的基本需求情况下 ,退耕坡地仍有很大潜力 ,以及从自然环境特点、历史时期植被分布来看 ,黄土高原广大地区种树种草是可行的 ;并提出了退耕还林 (草 )必须重视的有关问题     

黄土高原城郊区植被生产有机物价值的时空差异

选取受人类活动影响深刻的生态脆弱区陕北黄土高原城郊区为研究区,利用研究区太阳辐射、降水量、日照率、地面长波辐射、土地利用等数据和区域生态服务价值测算模型测算了研究区植被净生产力、生产有机物价值的时空差异.结果表明:陕北黄土高原城郊区各类植被净生产力年际间变化大;陕北黄土高原城郊区植被净生产力空间差异显著,而且同一区域不同植被类型净生产力也不相同;陕北黄土高原城郊区植被生产有机物总价值随时间变化明显,其中榆林市城郊区年际间变化最大.     

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau,China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types(5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics(including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process(8–50 years).     

Effects of agriculture,climate, and policy on NDVI change in a semi-arid river basin of the Chinese Loess Plateau

In 1999, the Grain for Green Project was implemented by the Chinese government. Since then, the vegetation of Zuli River Basin, a semi-arid river basin of the Chinese Loess Plateau, has been greatly changed. Clearly understanding the impact of natural and artificial factors on vegetation change is important for policy making and ecosystem management. In this study, spatio-temporal variations in vegetation cover in Chinese Zuli River Basin during 1999–2016 were investigated using Landsat normalized difference vegetation index (NDVI) data. Analyses of several indicators, including changes in NDVI in different slopes and land use changes and the relationships between climatic factors and NDVI change, were presented to quantitatively evaluate the effects of agriculture, climate, and policy on NDVI change. The NDVI in the Zuli River Basin increased during the study period, and the main contributors to this change were forest in 1999–2011, cropland, abandoned farmland, and grassland in 2009–2016, and land with slopes ≤ 15°. Land with slope > 15°, where the “Project” was implemented, slightly contributed to the increase in regional NDVI. In 1999–2011, the project (?98.16%) combined with climate change (?68.18%) showed negative effects on the increase in NDVI in the Zuli River Basin, but agriculture (22.28%) played a positive role in increasing this index. In 2009–2016 and 1999–2016, the project (38.45% and 35.25%, respectively), the project combined with climate change (49.83% and 46.30%, respectively), agriculture (18.61% and 23.30%, respectively), promoted increases in NDVI in the basin.     

近300年来黄土高原耕地变化及时空格局分析

以黄土高原过去300年来的耕地栅格数据为基础,运用ESDA(探索性空间分析方法)对黄土高原近300年来各县(旗)区的耕地变化情况进行了动态实证分析。结果表明:1)在过去的300年中,黄土高原耕地面积呈现出从增加到减少,然后又到增加的趋势;2)黄土高原各县(旗)域耕地面积存在着显著的空间集聚效应,并且各县(旗)域Moran's I指数都为正;3)黄土高原各县(旗)耕地面积的两种集聚类型("高高"低低")在时空上存在着明显的分带现象,且变化规律存在着显著的空间分异特征。     

Human induced dryland degradation in Ordos Plateau,China, revealed by multilevel statistical modeling of normalized difference vegetation index and rainfall time-series

Land degradation causes serious environmental problems in many regions of the world,and although it can be effectively assessed and monitored using a time series of rainfall and a normalized difference vegetation index(NDVI)from remotely-sensed imagery,dividing human-induced land degradation from vegetation dynamics due to climate change is not a trivial task.This paper presented a multilevel statistical modeling of the NDVI-rainfall relationship to detect human-induced land degradation at local and landscape scales in the Ordos Plateau of Inner Mongolia,China,and recognized that anthropogenic activities result in either positive(land restoration and re-vegetation)or negative(degradation)trends.Linear regressions were used to assess the accuracy of the multilevel statistical model.The results show that:(1)land restoration was the dominant process in the Ordos Plateau between 1998 and 2012;(2)the effect of the statistical removal of precipitation revealed areas of human-induced land degradation and improvement,the latter reflecting successful restoration projects and changes in land management in many parts of the Ordos;(3)compared to a simple linear regression,multilevel statistical modeling could be used to analyze the relationship between the NDVI and rainfall and improve the accuracy of detecting the effect of human activities.Additional factors should be included when analyzing the NDVI-rainfall relationship and detecting human-induced loss of vegetation cover in drylands to improve the accuracy of the approach and eliminate some observed non-significant residual trends.     

黄土高原历史时期植被变化

研究黄土高原历史时期植被变化是认识其环境演变的基础。文章在文献研究的基础上分析了黄土高原历史时期的植被变化。得出:西周以前及西周战国时期黄土高原植被保持着天然状态;秦汉时期天然植被仍占较大比重,人类活动尚没有改变黄土高原的植被面貌;唐宋时期河谷、平原地区已无天然森林,丘陵、山地植被也遭到破坏,北部沙漠开始扩张,自然环境处在恶化之中;明清时期植被遭到毁灭性破坏。造成黄土高原历史时期植被变化的根本原因是人为开垦土地,采伐森林和过度放牧。据推算春秋战国时期黄河中游森林覆盖率为53%;秦汉时期下降为42%;唐宋时期下降至32%;明清时期下降至4%。黄土高原濯濯童山主要是近600多年来人类活动对植被破坏的结果。     

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau,China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term(2004―2016) experimental data in the northern Loess Plateau region, China. Soil bulk density(BD), saturated soil hydraulic conductivity(Ks), field capacity(FC) and soil organic carbon(SOC) in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland(korshinsk peashrub), artificial grassland(alfalfa), fallow land and cropland(millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage(SWS) significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland(alfalfa) and shrubland(peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.     

陇东黄土高原土地利用、覆盖变化及驱动力分析

从土地利用和土地覆被的角度出发，利用RS和GIS技术，分析了20世纪最后15a该区土地利用和土地覆被变化在数量、结构和类型上的特点，并进一步分析了该区土地利用／土地覆被变化的驱动力，得出以下结论。15a间除建设用地和草地面积增加外，其他土地利用类型都呈现出不同程度减少。其中耕地减少了20691hm^2，主要转变为建设用地，且减少的耕地多为位置相对优越。产量较高的优质良田；林地减少了12269hm^2，主要转变为草地、早地和建设用地；草地的面积增加了33488hm^2，主要源自干林地和耕地的变化；交通建设用地高速增长，15a间增加了9278．8hm^2。该区土地利用和土地覆被变化的驱动力主要为自然因素、人口压力、经济因素及宏观政策等。     

黄土高原退耕还林措施对深层土壤含水率的影响

深层土壤水分分布状况对于黄土高原植被恢复和农业可持续发展意义重大。对陕北黄土区不同退耕还林措施(1979年种植的侧柏林、油松林和苹果林)及农地(对照)20 m深土壤剖面的土壤水分、根系分布状况及土壤粘粒含量进行了取样分析。结果表明:退耕还林措施显著降低了土壤含水率,总体表现为农地(11.30%)苹果林(6.66%)≈油松林(6.48%)≈侧柏林(5.92%)。深层土壤含水率同时受植物根系和土壤质地的影响,植物根系是影响4~10 m土壤含水率的主要因素,根系通过吸水作用降低了土壤含水率,但随着深度的增加,根系对土壤含水率的影响逐渐减弱,土壤质地对土壤含水率的影响逐渐增强,土壤含水率与土壤粘粒含量之间呈正相关关系。侧柏人工林根系影响土壤水分深度可达18 m,油松林的影响深度为16 m,35 a树龄的苹果林耗水深度为19 m左右。     

Scenario simulation of water retention services under land use/cover and climate changes: a case study of the Loess Plateau,China

Comprehensive assessments of ecosystem services in environments under the influences of human activities and climate change are critical for sustainable regional ecosystem management. Therefore, integrated interdisciplinary modelling has become a major focus of ecosystem service assessment. In this study, we established a model that integrates land use/cover change (LUCC), climate change, and water retention services to evaluate the spatial and temporal variations of water retention services in the Loess Plateau of China in the historical period (2000-2015) and in the future (2020-2050). An improved Markov-Cellular Automata (Markov-CA) model was used to simulate land use/land cover patterns, and ArcGIS 10.2 software was used to simulate and assess water retention services from 2000 to 2050 under six combined scenarios, including three land use/land cover scenarios (historical scenario (HS), ecological protection scenario (EPS), and urban expansion scenario (UES)) and two climate change scenarios (RCP4.5 and RCP8.5, where RCP is the representative concentration pathway). LUCCs in the historical period (2000-2015) and in the future (2020-2050) are dominated by transformations among agricultural land, urban land and grassland. Urban land under UES increased significantly by 0.63×10³ km²/a, which was higher than the increase of urban land under HS and EPS. In the Loess Plateau, water yield decreased by 17.20×10⁶ mm and water retention increased by 0.09×10⁶ mm in the historical period (2000-2015), especially in the Interior drainage zone and its surrounding areas. In the future (2020-2050), the pixel means of water yield is higher under RCP4.5 scenario (96.63 mm) than under RCP8.5 scenario (95.46 mm), and the pixel means of water retention is higher under RCP4.5 scenario (1.95 mm) than under RCP8.5 scenario (1.38 mm). RCP4.5-EPS shows the highest total water retention capacity on the plateau scale among the six combined scenarios, with the value of 1.27×10⁶ mm. Ecological restoration projects in the Loess Plateau have enhanced soil and water retention. However, more attention needs to be paid not only to the simultaneous increase in water retention services and evapotranspiration but also to the type and layout of restored vegetation. Furthermore, urbanization needs to be controlled to prevent uncontrollable LUCCs and climate change. Our findings provide reference data for the regional water and land resources management and the sustainable development of socio-ecological systems in the Loess Plateau under LUCC and climate change scenarios.     

黄土高原气候变迁、植被演替与土壤干层的形成

2 .5Ma B.P.以来 ,受地球轨道要素周期性变化和青藏高原阶段性强烈隆升的影响 ,黄土高原地区气候存在着干期与湿润交替出现的现象 ,但总的趋势是向干旱化方向演化。黄土高原第四纪以来草本植物一直较为繁茂 ,木本植物仅在少数几个时期处于优势地位。现代黄土高原人工林草植被普遍存在着土壤干层问题。土壤干层的形成是气候干旱化过程中必然出现的现象 ,它是导致植被演替的直接原因之一。人工植被激发并强化了土壤干层的形成。土壤干层的形成是气候干旱化和人工植被选择不当两个方面综合作用的结果 ,但有望通过有关人工措施使其危害得到缓解     

黄土高原乡村生态建设模式及效应分析--以延川县刘马家圪塔村为例

在实际调研的基础上,评价了陕北黄土高原延川县刘马家圪塔村现行生态建设模式,并利用对比分析法、相关分析法及趋势线分析法,分析该模式带来的经济效应,特别运用土地利用结构特征指数、土地利用动态变化模型及垦殖指数等分析了土地利用结构变化过程,对建设进程中出现的问题提出调控对策。     

黄土高原土壤水分与植被生产力的关系

土壤水分生态条件的恶化愈来愈成为黄土高原植被建设和生态环境建设的限制因素，我们在对黄土高原土壤水分生态因素分析的基础上，探讨了黄土高原土壤水分的季节性变化、土壤剖面水分变化、区域水分变异规律，分析了土壤水分与植被生产力间的相互关系，并提出了改善黄土高原土壤水分生态环境、提高植被生产力的调控技术。