Loess Plateau Of Central China Research Articles

Relationship between Ecosystem-Services Trade-Offs and Supply–Demand Balance along a Precipitation Gradient: A Case Study in the Central Loess Plateau of China

Although the theory of ecosystem services (ESs) is important for guiding land-use planning, knowledge of ESs trade-offs and supply–demand mechanisms is still lacking, and the characteristics of the correlation between the size of trade-offs and the balance between supply and demand along the precipitation gradient have not yet been clarified. In order to supplement this area of knowledge of ESs, we selected 30 small watersheds in high-, medium- and low-precipitation areas as study units. A biophysical model and socio-economic data were used to calculate supply and demand for carbon sequestration, soil conservation and water yield. Redundancy analysis and regression analysis were used to study the ESs trade-offs, the supply–demand dynamics, and the characteristics of their correlation. The results were as follows. (1) The supply and balance between supply and demand of the three ESs, the trade-off between carbon sequestration and water yield and the trade-off between soil conservation and water yield trended downwards from the high-precipitation area to the medium-precipitation area to the low-precipitation area. (2) The primary factors influencing balance between supply and demand with regard to carbon sequestration in high-, medium- and low-precipitation areas were population density and soil organic-matter content, and the size of the conditional effects were greater than 53%. The dominant factor affecting the balance between supply and demand with regard to soil conservation in the three precipitation areas was slope gradient, and the conditional effect was greater than 40%. The most significant determinants of balance between supply and demand with regard to water yield in the three precipitation areas were grassland area, forest area and precipitation, and the conditional effects were greater than 22%. (3) The most significant determinants of the trade-off between carbon sequestration and water yield in high-, medium- and low-precipitation areas were forest, soil organic-matter content and population density, and the conditional effects were all greater than 45%; the primary factors affecting the trade-off between soil conservation and water yield in high-, medium- and low-precipitation areas were grassland and slope gradient, and the conditional effects were all greater than 24%. (4) The relationship between the balance between supply and demand and trade-off size often followed a quadratic function; the next-most-common relationship was a monotonous nonlinear response, and a linear response relationship was relatively rare. This study revealed the factors influencing balance between supply and demand and trade-offs with regard to ESs and the characteristics of their correlations in areas with different degrees of precipitation, which provided a new idea for the synchronous regulation of ESs in the context of conflicts and supply–demand imbalance.

Afforestation Alters the Molecular Composition of Soil Organic Matter in the Central Loess Plateau of China

Many studies have been conducted on organic carbon changes under different land use patterns, but studies and data concerning changes in the molecular composition of soil organic matter (SOM) during land use conversion are scarce. In this work, we studied the chemical composition of SOM on two Robinia pseudoacacia L. plantations and their adjacent croplands in the Loess Plateau using biomarker and nuclear magnetic resonance (NMR) techniques. Experimental data on the molecular composition of SOM showed that the soil microbial biomass carbon content initially decreased and then returned to the original level gradually after afforestation, while the SOM content and stocks increased over time. At the initial stage of afforestation, the content of total solvent extracts did not change significantly but changed slowly over time in the plantations without artificial disturbance. With an increase in restoration time, the concentrations of both the microbial- and plant-derived solvent extracts increased. Moreover, the concentrations of plant-derived solvent extracts were consistently lower than those of microbial-derived solvent extracts. Afforestation also significantly increased the lignin-derived phenol content in the surface soil layer (0–10 cm). However, no obvious change was observed in the lignin-derived phenols of the two adjacent croplands. These results indicate that the accumulation of aboveground litter and underground roots has the strongest effects on the lignin-derived phenol content. In contrast to cropland, the two plantations exhibited a high degree of degradation of lignin-derived phenols in the surface soil, but this remained almost unchanged over time. Moreover, in contrast to 20 years after the establishment of the R. pseudoacacia plantation, the low alkyl/O-alkyl carbon ratio of the 8-year R. pseudoacacia plantation indicated that more easily degradable components accumulated during the initial stage of afforestation. Therefore, the proportion of the unstable carbon pool was relatively high and the SOM content may decline in the early stage of afforestation. These results provide evidence illustrating the detailed changes in the chemical composition of SOM during the ecological restoration process.

Palynological data confirm the occurrence of forest on the Loess Plateau of central China during the Middle Quaternary (MIS13)

The Loess paleosol sequence S5SS1 (top layer of S5 paleosol layers; marine isotope stage (MIS) 13) has been extensively studied because it is the most developed paleosol layer among all Quaternary soils in the China loess and represents the greatest humidity since the past 2.5 Ma. The question of whether forests occurred on the Loess Plateau tablelands when these paleosols were deposited is still a controversial scientific issue. This research provides a quantitative reconstruction of the past climate and forest cover between 544 and 480 ka based on a high-resolution pollen record together with magnetic susceptibility (χfd) and L*a*b* color parameters. Results suggest that the Luochuan area (central Loess Plateau) was sparsely covered by temperate deciduous forest under warm and humid conditions with a strong East Asian summer monsoon. The precipitation and woody cover during 544 and 531 ka were similar to those today and much greater than modern from 531 to 480 ka. Our findings are supported by paleosol profile research and modern vegetation studies. This study confirms that MIS 13 was a warm and humid period and that sparse forest developed on the tablelands of the central Loess Plateau, which provides new thinking on the ecosystem restoration program of the Loess Plateau.

Analysis of loess landslide mechanism and numerical simulation stabilization on the Loess Plateau in Central China

Loess landslides have complicated deformation mechanisms. Accurately describing the internal failure deformation of loess landslides and establishing a theoretical method of landslide instability evaluation for the prevention of subsequent landslides have become important topics in western development project construction in China. This paper presents a case study of the Zhonglou Mountain landslide in Shaanxi Province, China. Based on field investigation results, a two-dimensional stability analysis model was constructed using the finite element method. Taking the deformation characteristics of the landslide as the research basis, the distribution laws of the displacement, stress, and shear strain of this landslide were identified with the strength reduction finite element numerical simulation method. Additionally, the safety factor was evaluated under normal and storm conditions. The numerical simulation results show that the horizontal tensile stress of the landslide was mainly distributed in the middle and upper parts of the landslide under normal conditions, while the vertical tensile stress was distributed near the sliding surface. Under heavy rainfall, the sliding force increased, and the anti-sliding force and anti-sliding section decreased; the location of the maximum shear strain shifted down from the middle and upper parts of the landslide body to the area with a shear crack, and the plastic shear strain area expanded along nearly the entire the sliding surface, leading to the occurrence of a landslide. Thus, the use of anti-slide piles to stabilize the landslide was proposed and tested. Monitoring points were arranged along the sliding surface to evaluate the displacement, stress, and strain responses. The on-site observation results agreed with the modeling results. The use of anti-slide piles was demonstrated to be an effective stabilization method for the Zhonglou Mountain landslide.

One third of the abiotically-absorbed atmospheric CO2 by the loess soil is conserved in the solid phase

It has frequently been noticed that alkaline soils in arid and semiarid areas can absorb atmospheric CO2 abiotically. However, the fate of the absorbed CO2 is largely unknown, limiting our ability to accurately assess the contribution of abiotic CO2 absorption to carbon sequestration. The hypothesis that some abiotically-absorbed carbon could be fixed in the soil solid phase is yet to be explicitly tested. From April to November 2016, we added 13CO2 to the natural alkaline loess soil at a depth of 0–17 cm and quantified the proportion of 13CO2 conserved in the soil solid phase on the central Loess Plateau of China. The results showed that natural surface soil absorbed 13CO2 at a rate of 475.9 mg m−2 d−1. Of the absorbed 13CO2, 33.2% was conserved in the soil solid phase. The rate of added 13CO2 conserved in the solid phase was positively correlated with mean monthly soil water content but negatively correlated with mean monthly soil temperature. Our results indicated that, loess soil can absorb CO2 from the atmosphere through abiotic processes, and part of the abiotically-absorbed CO2 is stably fixed in the soil solid phase. Soil with a higher water content and lower temperature may promote the abiotic CO2 fixation. The rate of CO2 fixation through abiotic processes at the surface soil accounted for approximately 10%-20% of the reported local annual net ecosystem exchange, implying that the abiotic CO2 uptake by loess soil may play an important role in assessing the capacity of CO2 sequestration in these areas.

Effects of Robinia pseudoacacia afforestation on aggregate size distribution and organic C dynamics in the central Loess Plateau of China: A chronosequence approach

Afforestation has been proven to have enormous potential for carbon (C) sequestration; however, the dynamics of aggregate-associated organic carbon (OC) following afforestation and their contribution to changes in bulk soil OC are not well understood in regions with serious soil erosion. Therefore, we investigated the dynamics of OC associated with aggregates along a Robinia pseudoacacia (RP) afforestation chronosequence in the Loess Plateau. Soil aggregate size distribution and OC dynamics in bulk soil were analyzed 10, 18, 28, and 42 years after RP afforestation at depths of 0–20 cm and 20–40 cm. Results showed that total macroaggregates (>0.25 mm), mean weight diameter, and geometric mean diameter increased significantly with stand age, after 42 years of afforestation, increased by 433.5%, 437.2%, 302.1% in the 0–20 cm depth, respectively, while microaggregate amounts decreased by 52.9%, and the proportions of silt + clay fraction showed no obvious changes. Long-term afforestation increased OC content and stock, both in bulk soil (245.6% and 222.9% in the 0–20 cm depth, respectively) and soil aggregates. The improvement of soil structure and enrichment of OC stocks were greater at the 0–20 cm depth than the 20–40 cm depth. In addition, small macroaggregates (2–0.25 mm) contained the highest OC content and microaggregates (<0.025 mm) had the highest OC stocks regardless of soil depth and stand age. Across the afforestation chronosequence, OC content and stock in bulk soil positively correlated with large macroaggregate (>2 mm) amounts and small macroaggregate (2–0.25 mm) associated OC dynamics (P < 0.01). These results indicated that changes in bulk soil OC dynamics mainly depend on changes in the proportion of large macroaggregates and in the OC dynamics associated with small macroaggregates after RP afforestation.

A quantitative model to simulate the vertical errors of SRTM3 DEM V4 data at the pixel level in the Shanbei Plateau of China

ABSTRACT The Shanbei Plateau is located in the central Loess Plateau of China, which exhibits typical loess geomorphology and suffers serious soil and water erosion. Numerous studies are conducted here using digital topographic analysis methods based on digital elevation model (DEM) datasets. Most of these topographic analyses are conducted at the pixel level; thus, it is meaningful to determine the vertical error distributions of the DEM datasets at that scale. Taking the 14th product of the Geoscience Laser Altimeter System on the Ice, Cloud, and land Elevation Satellite (ICESat/GLA14) as the benchmark, the aim of this research is to construct a quantitative model to simulate the vertical error distributions of SRTM3 (Shuttle Radar Topography Mission with a spatial resolution of 3”) DEM V4 data for the Shanbei Plateau. Through comparison, the multiple linear regression (MLR) model is chosen and the vertical error surface is determined based on the MLR model and the land surface factor data. Moreover, the rectified SRTM3 DEM V4 data are developed based on the original data version and the vertical error surface. Through accuracy assessment, the root mean squared error (RMSE) value for the rectified version is found to be 9.6 m. Compared to 20.6 m for the original version, this is a clear improvement. Meanwhile, the MLR model has an R 2 (the coefficient of determination) value of 0.484, which shows that it is able to represent the relationships between the vertical error distributions and the land surface factors. This research is not only meaningful for digital topographic analysis and its relevant fields of application but also provides a reference for accuracy assessments of other DEM datasets in different regions.

Changes in maximum daily runoff depth and suspended sediment yield on the Loess Plateau, China

The maximum river flow is of important reference significance to flood disaster prevention on the Loess Plateau of central China. However, due to the lack of hydrological data, previous studies have rarely explored spatiotemporal changes in the annual maximum daily runoff depth (Hmax) and annual maximum daily suspended sediment yield (SSYmax) of rivers in this region. This study uses daily discharge data and daily sediment concentration data from 104 hydrological stations on the plateau to compare the Hmax and the SSYmax during period P1 (1971–1987) and period P2 (2008–2016). The results show that 66% of stations exhibited a significant decline in multi-year mean Hmax from P1 to P2 (p < 0.05). However, the multi-year mean SSYmax showed more widespread changes, with 77% of stations seeing a significant decline (p < 0.05). And on average, the runoff on the day of Hmax contributed 6.6% and 5.8% of the annual runoff during P1 and P2, respectively; by contrast, SSYmax contributed 27.9% and 33.5%, respectively, to the total annual suspended sediment yield in P1 and P2. Analyses using Spearman’s rank correlation coefficient indicate that the spatial distribution of Hmax has larger variability than SSYmax during both P1 and P2 and that the spatial distribution pattern of SSYmax during P2 is more unstable than during P1. We found that the suspended sediment concentration (SSC) on the day that Hmax occurs (SSChmax) remained relatively stable for most stations studied within the loess gullied-hilly area across the Loess Plateau, but the stable SSChmax value during P1 differed from the value during P2. We conclude that human activities (e.g., afforestation, terracing, and construction of check dams) may be the cause of the differing SSC values during peak discharge between the two periods. We also found that the average percentage of years in which Hmax and SSYmax occurred on the same day on the plateau was 55%. Many factors can lead to Hmax and SSYmax happening asynchronously, such as heavy runoff events lasting several consecutive days, the characteristics of a particular basin, and the influence of human activities. These results provide information that will be useful for understanding how to manage extreme hydrological events on the Loess Plateau.

黄土高原林下草地对模拟增温的短期响应

气候变暖在高海拔山地更为明显，山地植被对气候变暖响应的空间格局将成为山地研究新的热点。在黄土高原东部沿纬度梯度选择北段管涔山、中段关帝山和南段五鹿山，分别划分高、中、低3个海拔梯度，每一梯度用开顶式生长室设置对照（CK）、低度增温（LW）、高度增温（HW）3种模拟增温样地，于增温1年后植被生长季调查山地林下草本群落的生长特征及水热因子，探究黄土高原林下草地对气候变暖的短期响应及其随纬度、海拔的变化格局。结果表明：在LW和HW处理下，（1）空气温度增加0.47℃和1.00℃，空气湿度增加1.37%和1.94%，其中空气温度增幅随海拔增加显著增大（P=0.012）；（2）土壤水分减小0.32%和0.64%，土壤温度减小0.07℃和增加0.06℃，其中土壤温度增幅随纬度增加显著减小（P=0.003）；（3）植物密度增加41.27株/m²和78.53株/m²，植物高度增加0.04 m和0.03 m，植物频度增加5.47%和3.47%，而植物盖度显著增加5.32%和0.88%（P=0.042）；（4）植被与温度关系的相关系数绝对值增加31.49%和56.82%，与水分关系的相关系数绝对值增加38.67%和62.89%。因此，山地温度对增温响应更大，且空气温度具正向海拔依赖性，土壤温度具负向纬度依赖性；增温加强植被与水分的关系，促进植物对水的依赖性，进而显著影响植物盖度。然而，增温的短期效应易受到降雨条件的影响，使结果出现误差，故在类似的研究中建议加强试验的时间尺度。;Climate warming is more obvious in high-altitude mountains, and as a result, investigating the spatial patterns of mountainous vegetation responses to climate warming is becoming a new hot spot of mountain research. The Luliang Mountain Range lies on the east side of the Loess Plateau in central China and is characterized by an extremely fragile environment due to the lack of precipitation. Based on latitudinal gradients from north to south in the Luliang Mountain Range, the affiliated Guancen Mountain in its northern section, Guandi Mountain in its central section, and Wulu Mountain in its southern section were selected as study area. Each of these mountains was divided into three gradients: high altitude, medium altitude, and low altitude. The corresponding elevations for the high, medium, and low altitudes were 2571.3 m, 2395.0 m, and 2222.4 m for Guancen Mountain, 2179.1 m, 2000.7 m, and 1899.7 m for Guandi Mountain, and 1602.0 m, 1458.6 m, and 1318.0 m for Wulu Mountain, respectively. Three experimental plots heated by open-top chambers (OTCs) were placed within each altitudinal gradient. Treatments were implemented using completely randomized block design and including control (CK), low temperature increase (LW), and high temperature increase (HW). During the growing season in 2017, the growth characteristics and hydrothermal factors of the herbaceous communities in mountainous forests were surveyed in order to explore the responses of herbaceous communities to climate warming as well as the spatial pattern changes of these responses with latitudinal and altitudinal gradients. The results revealed the following under the LW and HW treatments: (1) air temperature increased by 0.47℃ and 1.00℃, respectively. The atmospheric relative humidity increased by 1.37% and 1.94%, respectively. The increasing amplitude of air temperature grew significantly with altitude (P = 0.012). (2) Corresponding soil moisture decreased by 0.32% and 0.64%, respectively. The soil temperature decreased by 0.07℃ and increased by 0.06℃. The increasing amplitude of soil temperature diminished significantly with latitude (P = 0.003). (3) The respective vegetation density increased by 41.27 plants/m² and 78.53 plants/m², but vegetation height increased by 0.04 m and 0.03 m. The vegetation frequency increased by 5.47% and 3.47%, while vegetation coverage significantly increased by 5.32% and 0.88% (P = 0.042). (4) The relationships among vegetation indices, temperature factors, and moisture factors using RDA ordination analysis indicated that the absolute value of the correlation coefficient between vegetation and temperature increased by 31.49% and 56.82%, as well as that between vegetation and moisture correspondingly increased by 38.67% and 62.89%, respectively. Therefore, in the Luliang Mountain Range, temperature factors were more responsive to warming, with air temperature being positively correlated with altitude and soil temperature being negatively correlated with latitude. However, the warming effects from the OTCs strengthened the relationship between vegetation and moisture, which promoted the dependence of plants on moisture, thereby significantly affecting vegetation coverage. Warming should be controlled in terms of amplitude, which will then have positive effects on vegetation. When precipitation occurred during the experiment, however, the associated moisture enhancement could weaken the warming effects on the soil. Thus the soil temperature decreased during warming treatments, indicating that precipitation had a greater influence on warming effects in regions where precipitation dominated the environmental factors. Therefore, the effects of short-term warming were affected largely by rainfall, which introduced errors into the results. We strongly suggest that the experimental duration should be prolonged in similar studies on warming effects in order to reduce these errors.

Soil Water Availability Drives Changes in Community Traits Along a Hydrothermal Gradient in Loess Plateau Grasslands

Plant functional traits can be used to predict ecosystem responses to climate gradients, yet precipitation explains very little variation for most traits. Soil water availability directly influences plant water uptake and thus may assist with the improvement of plant trait–water relationships. However, this promise remains poorly realized due to rare tests. Here, we provide the first study that attempts to link climate factors, vertical soil water availability, and community composition at a regional scale. Our study paired field-measured vertical soil available water (0–300 cm) and community functional composition at 46 herbaceous grassland sites along a steep hydrothermal gradient in the Loess Plateau of Central China. Community functional composition was expressed via community-weighted means of eight traits. Structural equation modeling was employed to evaluate the role of vertical soil available water content, controlled by precipitation and air temperature, in affecting plant community-weighted traits. We found that soil available water content at depths of 20–100 cm was typically responsible for mediating the effects of precipitation and air temperature on plant community composition. This emerged as the predominant factor to explain variations in grassland response traits, including leaf area, specific leaf area, and leaf dry matter content. These traits exhibited clear drought-induced shifts along soil desiccation gradients and responded to drier conditions by reducing leaf area/specific leaf area and increasing leaf dry matter content. Our findings rehighlighted soil water availability as the core driver that needs to be considered in the restoration and management of dryland ecosystems.

Interactive Effects of Climatic Factors on Seasonal Vegetation Dynamics in the Central Loess Plateau, China

The interactive effects of climatic factors (precipitation and temperature) on vegetation growth can be characterized by their effect on vegetation seasonal dynamics. The interactive effects, seasonal trend of vegetation growth, and its future consistency (potential for future trend) have not been adequately studied in the literature. In this work, using the Enhanced Vegetation Index (EVI) and gridded climate data at a resolution of 250 m in the central Loess Plateau region, we examined seasonal vegetation dynamics with climate changes and the interactive effects of climatic factors on vegetation growth at the pixel and regional scales from the period 2000 to 2015. Vegetation cover in the Central Loess Plateau in China has dramatically changed due to the Grain-for-Green (GFG) ecological restoration program, which was designed to convert cropland to forestland or grassland since 1999. Our results show that the EVI increased significantly during the 16 year period and is likely to continue to increase in the near future. Relatively small Hurst exponents for forestland suggests that the potential for a future increased trend will be weak for the forest. Large Hurst exponents for grassland indicate its strong potential of further increase. Significant increases in spring precipitation have promoted vegetation growth, while significant decreases in summer temperature have had negative effects on vegetation growth. For temperatures between 10 to 20 °C, the impact of temperature on vegetation growth has a clear positive relationship with the moderator variable precipitation. For precipitation &lt; 200 mm in the growing season, the impact of precipitation on vegetation growth has a clearly positive relationship with the moderator variable temperature. Results of this study will provide useful and important guidelines for designing forestland and grassland restoration plans in arid, semiarid and sub-humid regions.

Carbon Storage Dynamics of Secondary Forest Succession in the Central Loess Plateau of China

Research Highlights: This study comprehensively revealed the carbon sequestration characteristics of secondary forests in the central Loess Plateau during vegetation succession. Background and Objectives: The secondary succession of Loess Plateau forests is of great significance in global climate change, but their carbon storage dynamics are poorly understood. The study objectives were to clarify the pattern of changes and contribution level of carbon stocks in various components of ecosystem during succession. Materials and Methods: We selected 18 plots for Pinus tabuliformis Carr. forest at the early stage of succession, 19 for pine-broadleaved mixed forest at the middle stage, and 12 for Quercus-broadleaved mixed forest at the climax stage to determine the tree, shrub, herb, fine root, litter, coarse wood debris (CWD), and soil carbon stocks. Results: Ecosystem carbon stocks increased from 160.73 to 231.14 Mg·ha−1 with the succession stages. Vegetation (including tree, shrub and herb) and soil were the two largest carbon pools, and carbon was mainly sequestrated in tree biomass and shallow soil (0–50 cm). In the early stage, soil contributed more carbon stocks to the ecosystem than vegetation, but with succession, the soil contribution decreased while vegetation contribution increased, finally reaching a balance (46.78% each) at the climax stage. Fine root, litter, and CWD contributed little (average 6.59%) to ecosystem carbon stocks and were mainly involved in the turnover of vegetation biomass to soil carbon. Conclusions: Our results provide direct evidence for carbon sequestration of secondary forests on the Loess Plateau. The dynamic results of carbon storage provide an important basis for forest restoration management under climate change.

Effects of Stand Age on Biomass Allocation and Allometry of Quercus Acutissima in the Central Loess Plateau of China

We studied the effects of stand age on allocation and equation fitting of aboveground and below-ground biomass in four Quercus acutissima stands (14, 31, 46, and 63 years old) in the Central Loess Plateau of China. The stem wood, stem bark, branch, foliage, and belowground biomass of each of the 20 destructive harvesting trees were quantified. The mean total biomass of each tree was 28.8, 106.8, 380.6, and 603.4 kg/tree in the 14-, 31-, 46-, and 63-year-old stands, respectively. Aboveground biomass accounted for 72.25%, 73.05%, 76.14%, and 80.37% of the total tree biomass in the 14-, 31-, 46-, and 63-year-old stands, respectively, and stem wood was the major component of tree biomass. The proportion of stem (with bark) biomass to total tree biomass increased with stand age while the proportions of branch, foliage, and belowground biomass to total tree biomass decreased with stand age. The ratio of belowground biomass to aboveground biomass decreased from 0.39 in the 14-year-old stand to 0.37, 0.31, and 0.24 in the 31-, 46-, and 63-year-old stands, respectively. Age-specific biomass equations in each stand were developed for stem wood, stem bark, aboveground, and total tree. The inclusion of tree height as a second variable improved the total tree biomass equation fitting for middle-aged (31-year-old and 46-year-old) stands but not young (14 years old) and mature (63 years old) stands. Moreover, biomass conversion and expansion factors (BCEFs) varied with stand age, showing a decreasing trend with increasing stand age. These results indicate that stand age alters the biomass allocation of Q. acutissima and results in age-specific allometric biomass equations and BCEFs. Therefore, to obtain accurate estimates of Q. acutissima forest biomass and carbon stocks, age-specific changes need to be considered.

Measurement of the connectivity of runoff source areas on a bare soil surface in a laboratory experiment

As soil erosion has been severely constraining agricultural production and economic sustainability in the Loess Plateau in central China, study of hydrologic connectivity of tilled slope surfaces based on higher accuracy has major implications for prevention of soil erosion. This study explores the properties of hydrologic connectivity of microtopographic slope surfaces (contour tilled, at gradients of 15°, 20°, and 25° in respective events) under artificial rainfall (at 90 mm h⁻¹) produced in laboratory experiments. A spatial metric, flowlength, was acquired and tested to quantify the connectivity of runoff source areas and was calculated as the average lengths of the runoff pathways. The grid cells, which measured lengths of flow paths (6 to 10 mm) in runoff source areas at different slopes, accounted for over 46% of the total grid cells on the raster-based map. Flow path lengths increased when the slope gradient was steeper and decreased when the surface roughness increased. The ratio of the surface area connected to the outlet to the total surface area of the soil tank (C, %), which equals the parameter C, or the ratio of the surface runoff area connected to the downstream outlet to the total surface area of the study area, peaked quickly and then became stable under accumulative rainfall. The steeper the slope, the shorter amount of time it took for C to reach its peak; the greater the average C, the better hydrologic connectivity. Flowlength could be an important index for characterizing the structural properties of the hydrologic connectivity of a slope surface, and also simplified hydrograph and relative surface connection function can be used to characterize the runoff generation process and the mechanism of the soil surface and the properties of its hydrologic connectivity. These results are instrumental in providing guidelines on and insight into the role of hydrologic connectivity at a microtopographic scale.

Vegetation variation of loess deposits in the southeastern Inner Mongolia, NE China over the past ∼1.08 million years

The stable carbon isotopic composition of organic matter of aeolian silt deposits is regarded as an appropriate proxy index of paleovegetation, especially in the Chinese Loess Plateau in central China. In this study, a loess–paleosol sequence in the southeastern Inner Mongolia Autonomous Region in northeastern (NE) China, which is located outside the Chinese Loess Plateau, is chosen to reconstruct the vegetation history since ∼1.08 Ma. Temperature exhibits a threshold value, which determines the growth of C4 plants in this study area. The organic matter of the samples is derived from two different vegetation types, namely, the mixed C3 and C4 plants and the pure C3 plants. The δ13C of the organic matter shows negative values in loess units and higher values in paleosol units. This finding reflects the influence of temperature and summer monsoon intensity on the vegetation dynamics over glacial–interglacial cycles. On a longer time scale, the δ13C values are higher between ∼1.1 and ∼0.9 Ma and after ∼0.35 Ma, and lower between ∼0.9 and ∼0.35 Ma, which may be attributed to a long-term temperature variation. Our analysis shows that regional temperature is the most important limiting factor that forces vegetation changes at the glacial–interglacial time scale in NE China.

Holocene erosion triggered by climate change in the central Loess Plateau of China

Understanding changes in Holocene erosion is essential for predicting soil erosion in the future. However, the quantitative response of natural erosion to Holocene climate change is limited for the Loess Plateau of China. In this study, two soil profiles were investigated on the Luochuan and Yanchang sites in the central Loess Plateau of China; and four climate indicators, i.e. magnetic susceptibility, calcium carbonate content, total organic carbon content, and clay content (<0.005mm), were analyzed to describe climate change. The equations fitted using modern pedogenic susceptibility, precipitation, and temperature were used to quantitatively reconstruct paleoprecipitation and paleotemperature in the Holocene. The current relationship between soil erosion intensity and precipitation was determined and used to estimate historical erosion. Results indicated that climate was coldest and driest between 12,000 and 8500cal.yrBP, and became warmer and wetter during 8500 to 5500cal.yrBP. The warmest and wettest climate was from 5500 to 3000cal.yrBP and was getting colder and dryer over the last 3000years. Holocene erosion intensity changed with fluctuation of mean annual precipitation, and these changes were different on both sites. The peak erosion values were 20,966t·km−2·yr−1 in 7500cal.yrBP and 21,148t·km−2·yr−1 in 3300cal.yrBP on the Luochuan and Yanchang sites, respectively. Furthermore, more severe soil erosion with a faster increase was estimated on the Yanchang site than Luochuan site with a range between 6547 and 11,177t·km−2·yr−1 during the last 1800years. This study proposed a new method to quantify historical soil erosion triggered by climate change, which not only can derive detailed soil erosion intensity change with variation of climate, but also provide a way to compare soil losses between different areas.

Temporal variation and spatial scale dependency of ecosystem service interactions: a case study on the central Loess Plateau of China

An important feature of ecosystem service interaction is that it changes over time and across spatial scales. This research aims to find which ecosystem service interactions temporally vary and depend on spatial scale. We calculated six ecosystem services of the Baota District on the central Loess Plateau of China for 2000, 2005, and 2010. Furthermore, we quantified the interactions among these services at the beginning and after the end of the first phase of the Grain for Green Program in this area, and across the pixel scale of 1 km2 and the town scale. Water yield decreased significantly, and habitat quality, net primary productivity, and evapotranspiration increased significantly across different land use types from 2000 to 2005. The synergy between food productivity and water yield, and the trade-off between water yield and evapotranspiration, greatly reduced from 2000 to 2010 at the pixel scale. Water yield was a trade-off to habitat quality, NPP, and recreation capacity in 2000 at the pixel scale while a synergy to the three services in 2010. The synergies between habitat quality and NPP, evapotranspiration, and recreation capacity at the pixel scale were enhanced from 2000 to 2010. Changes in the direction or significance of correlations among ecosystem services were observed across the pixel and town scales in 2000 and 2010. This study contributes to increasing the understanding of the temporal variation of ecosystem service interactions caused by regional ecological restoration programs, and the spatial scale dependency of the interactions.

Effect of Microbial Carbon, Nitrogen, and Phosphorus Stoichiometry on Soil Carbon Fractions under a Black Locust Forest within the Central Loess Plateau of China

Core Ideas Soil C fractions were significantly correlated with microbial C/P and N/P ratios. Soil C fractions were extremely affected by microbial C/P and N/P ratios. Microbial C, N, and P stoichiometry have the potential to affect C storage. Microbial C/N/P stoichiometry ratios are of interest because of important ecosystem fluxes of C, N, and P, such as mineralization and immobilization, and they can help to characterize the cycling of soil elements, especially regarding soil C sequestration. However, it is not clear how soil microbial C/N/P stoichiometry influences C cycling. In this study, the concentrations of microbial biomass C, microbial biomass N, microbial biomass P, and soil C fractions were measured in 45‐, 40‐, and 25‐yr‐old black locust (Robinia pseudoacacia L.) forest soils and a sloped cropland. The results showed that soil organic C (SOC) concentrations or stocks and the percentage increment of the SOC stocks were highest under 45‐yr‐old black locust (RP45a). The concentrations of each C fraction in the black locust forest soils (45a, 40a, and 25a) were higher than that of sloped cropland in the 0‐ to 30‐cm soil profile. The concentrations of microbial C, N, and P in RP45a were also higher by an average of 29.6 to 232.9, 9.2 to 17.9, and 0.6 to 1.1 mg kg−1, respectively, compared with the same concentrations in sloped cropland at the 0‐ to 30‐cm soil depth. Redundancy analysis indicated that soil C fractions, especially for particulate organic C (53–2000 and &gt;2000 μm), were significantly correlated with the microbial C/P and N/P ratios, and the “best” model selection indicated that the microbial N/P and C/P ratios significantly changed with soil C fractions with regard to stand age and soil depth in the black locust forests. Therefore, the present study demonstrated that C fractions respond to microbial C, N, and P stoichiometry after farmland‐to‐forest conversion and hence have the potential to affect C storage in the loess hilly region.

Changes in vegetation carbon stocks between 1978 and 2007 in central Loess Plateau, China

To control soil and water loss and environmental degradation, shelter/protective forests were established in the Loess Plateau as a component of the Three-North Shelter Forest Program (TNSFP). With the development of the TNSFP in this region, the effects of shelter forests in the Loess Plateau on carbon (C) stock have been investigated. To assess the effects of shelter forests in the Loess Plateau on the C stock, we utilized the data obtained from field investigations and Landsat ETM+ images to assess the C stocks (aboveground and belowground carbon) of shelter forests in the central Loess Plateau in China (11.94 × 106 ha) during the TNSFP construction period (from 1978 to 2007). We also performed an uncertainty analysis up-scaling from field plots to the study area. The total vegetation C stocks increased significantly from 144 Tg in 1978, to 269 Tg in 2007, and shelter forests accounted for 80 % of total C stocks. The annual mean C sink was 4.28 Tg year−1 for the vegetation. Shelter forests were estimated to have sequestered 2.55 Tg year−1 biomass C and conserved 3.35 Tg year−1 soil C. These results suggest that the shelter forests in the central Loess Plateau have acted as a C sink since the initiation of the TNSFP in 1978. Furthermore, afforestation and reforestation have a significant effect on C sequestration.

Managing landscape heterogeneity in different socio-ecological contexts: contrasting cases from central Loess Plateau of China and southern Finland

Landscape transition drives environmental change across the globe. However, landscape and its change are complex with high spatial heterogeneity, which challenges strategic decision-making. This paper aims to derive management meaningful units based on landscape status and change analysis and the generalization of landscape spatial heterogeneity. Based on contrasting cases from Finland (Vanajavesi) and China (Baota District), this paper analyzed the landscape attributes and change since 2000. A k-means clustering approach was used to generalize the landscape types based on indicators of landscape composition and its change, spatial pattern, population, and income. Most significant change in land covers was the expansion of artificial surfaces, and the bi-directional transitions between agricultural areas and forests and semi-natural areas in Vanajavesi, while the expansion of artificial land and shrinkage of cropland were most significant in Baota District. Larger changes in landscape metrics were also observed in Baota District. Finally, three landscape clusters were generalized in both of the case areas. For each cluster, the landscapes and their change characteristics were interpreted as pertinent to the average land cover pattern and its change and socioeconomic conditions. Brief landscape management recommendations were also given for the resulting clusters. This paper contributes to enriching the understanding of the analysis and management of landscape spatial heterogeneity based on the information from both landscape status and change. The contrasting case analyses from an international perspective indicate the usefulness of clustering approach in accommodating spatial heterogeneity, which imply a regionalized need for landscape monitoring, assessment, and management.