Bojie Fu

The relationships between land use and soil conditions in the hilly area of the loess plateau in northern Shaanxi, China

Abstract Inappropriate land use is one of the main reasons for soil erosion and nutrient loss in the hilly loess area. In the Yangjuangou catchment, which has typical hill and gully topography, the effects of land use changes on soil erosion and the distribution of soil nutrients and moisture were studied at the three spatial scales of total catchment, transect and land use type. Between 1984 and 1996, forest and grassland increased by 36% and 5%, respectively, and slope farmland decreased by 43%. The land use changes decreased annual soil erosion by 24%. The amounts of total N, total P, available N, available P and organic matter of surface soil (0–20 cm) and of moisture in the 0–70 cm soil suggest that a farmland/grassland/forest land use structure from hill foot to hill top has a better capacity for soil conservation and retention of nutrients than other land use structures. The contents of soil nutrients are in the order forest>grassland>slope farmland, and those of soil water are forest

A Policy-Driven Large Scale Ecological Restoration: Quantifying Ecosystem Services Changes in the Loess Plateau of China

As one of the key tools for regulating human-ecosystem relations, environmental conservation policies can promote ecological rehabilitation across a variety of spatiotemporal scales. However, quantifying the ecological effects of such policies at the regional level is difficult. A case study was conducted at the regional level in the ecologically vulnerable region of the Loess Plateau, China, through the use of several methods including the Universal Soil Loss Equation (USLE), hydrological modeling and multivariate analysis. An assessment of the changes over the period of 2000-2008 in four key ecosystem services was undertaken to determine the effects of the Chinese governments ecological rehabilitation initiatives implemented in 1999. These ecosystem services included water regulation, soil conservation, carbon sequestration and grain production. Significant conversions of farmland to woodland and grassland were found to have resulted in enhanced soil conservation and carbon sequestration, but decreased regional water yield under a warming and drying climate trend. The total grain production increased in spite of a significant decline in farmland acreage. These trends have been attributed to the strong socioeconomic incentives embedded in the ecological rehabilitation policy. Although some positive policy results have been achieved over the last decade, large uncertainty remains regarding long-term policy effects on the sustainability of ecological rehabilitation performance and ecosystem service enhancement. To reduce such uncertainty, this study calls for an adaptive management approach to regional ecological rehabilitation policy to be adopted, with a focus on the dynamic interactions between people and their environments in a changing world.

Soil moisture variation in relation to topography and land use in a hillslope catchment of the Loess Plateau, China

The profile characteristics and the temporal dynamics of soil moisture variation were studied at 26 locations in Da Nangou catchment (3.5 km(2)) in the loess area of China. Soil moisture measurements were performed biweekly at five depths in the soil profile(0-5, 10-15, 20-25, 40-45 and 70-75 cm) from May to October 1998 using Delta-T theta probe. Soil moisture profile type and temporal variation type and their relationship to topography and land use were identified by detrended canonical correspondence analysis (DCCA) and correlation analysis. The profile distribution of time-averaged soil moisture content can be classified into three types i.e. decreasing-type, waving-type and increasing-type. The profile features of soil moisture (e.g. profile gradient and profile variability) are influenced by different environmental factors. The profile type of soil moisture is only attributed to land use while profile gradient and profile variability of soil moisture is mainly related to land use and topography (e.g. landform type and slope). The temporal dynamics of layer-averaged soil moisture content is grouped into three types including three-peak type, synchro-four-peak type and lagged-four-peak type. These types are controlled by topography rather than by land use. The temporal dynamic type of soil moisture shows significant correlation with relative elevation, slope, aspect, while temporal variance displays significant relation with slope shape. The mean soil moisture is related to both the profile and dynamics features of soil moisture and is controlled by both land use and topography (e.g. aspect, position, slope and relative elevation). The spatial variability of soil moisture across landscape varies with both soil depths and temporal evolution

The effects of land use on soil moisture variation in the Danangou catchment of the Loess Plateau, China

Abstract Soil moisture plays a critical role in both crop growth and vegetation restoration in semiarid environments. Its spatial and temporal variability results from topography, soils, vegetation and land uses. However, little knowledge exists about the effects of land use structure on soil moisture variability. In order to analyze soil moisture variations in relation to land use patterns, five land use structures and seven land use types were selected to monitor soil moisture. Soil moisture measurements were performed biweekly at 26 locations in a small catchment on the Loess Plateau of China from May to October 1998. The measurements were taken using a Theta-Probe at five depths of soil profile (0–5, 15–20, 25–30, 45–50 and 70–75 cm). These data were analyzed for soil moisture variations in space and time for seven land use types. Three peaks and three troughs of soil moisture variations during the growing season were found. The influence of shrubland on mean soil moisture within 0–70 cm was significantly different from that of cropland, orchard and intercropping land. Three types of soil moisture changes in profile were classified as increasing, decreasing and waving types. An analysis of the differences in soil moisture for five land use structures indicated that the influences of land use patterns on soil moisture were complex. This study provides an insight into the implications for hydrological modeling, runoff and erosion control in this area.

Effect of land use conversion on soil organic carbon sequestration in the loess hilly area, loess plateau of China

Changes in land use may alter land cover, which results in carbon stock changes in biomass as well as in the soil. In China’s loess plateau, vegetation restoration has been conducted since 1950s to control soil erosion and improve the ecosystem, with significant investment of money and manpower. Despite these efforts, soil erosion has still been severe. To reduce soil erosion and improve land quality, China initiated another state-funded project, Grain-for-Green, in 1999 in the loess plateau. However, it is not clear how effective this newly initiated project will be. In this study, we evaluated the effect of land-use conversion on soil organic carbon (SOC) and the potential effect of the current project on SOC sequestration in the Anjiapo catchment area of the loess hilly area of the loess plateau in China. This evaluation is based on SOC measurements in cropland versus in other converted land use types. We found that SOC sequestration mainly occurred in the surface soil after land use conversion took place. Land use conversion from cropland to shrubland or wild grassland (i.e. undisturbed land) was better for SOC sequestration than tree plantation in the semi-arid loess hilly area. By using the land use change in the study area as a scenario, the potential contribution of land use change on SOC sequestration due to the Grain-for-Green project was estimated. It was found that this project in the loess plateau of China would be helpful for SOC sequestration if successfully implemented.

Three Gorges Project: Efforts and challenges for the environment

The Three Gorges Project has been subject to intense debates regarding its benefits and costs. The environmental impacts of this huge project have been an important focus of these debates since the project planning stage. After the operation of the Three Gorges Dam at full capacity at the end of 2008, new environmental and ecological issues are emerging. This paper gives a brief description of the Three Gorges Project and its environmental impact assessment process, as well as major efforts to control environmental problems brought about by the project. From the long and complicated evaluation process, it is clear that there are large uncertainties and competing opinions regarding the benefits and costs, especially the ecological and environmental ones, of the project even after great research effort. Emphasis here is given to the environmental challenges including: (1) water quality control; (2) water and sediment regulation; (3) biodiversity conservation in the riparian and aquatic ecosystems; (4) environmentally friendly dam operation and regional sustainable development. Opportunities often grow out of the challenges. The Three Gorges Project provides opportunities for grand-scale experiments on the environmental, ecological, and socio-economic impacts of large dams. Local, national, and international concerted efforts and concrete actions should be directed to the mitigation and control of the negative impacts as well as securing the positive contributions of the project across scales.

How ecological restoration alters ecosystem services: an analysis of carbon sequestration in China's Loess Plateau

Restoring disturbed and over-exploited ecosystems is important to mitigate human pressures on natural ecosystems. China has launched an ambitious national ecosystem restoration program called Grain to Green Program (GTGP) over the last decade. By using remote sensing techniques and ecosystem modelling, we quantitatively evaluated the changes in ecosystem carbon sequestration since Chinas GTGP program during period of 2000–2008. It was found the NPP and NEP in this region had steadily increased after the initiative of the GTGP program, and a total of 96.1 Tg of additional carbon had been sequestered during that period. Changes in soil carbon storage were lagged behind and thus insignificant over the period, but was expected to follow in the coming decades. As a result, the Loess Plateau ecosystem had shifted from a net carbon source in 2000 to a net carbon sink in 2008. The carbon sequestration efficiency was constrained by precipitation, and appropriate choices of restoration types (trees, shrubs, and grasses) in accordance to local climate are critical for achieving the best benefit/cost efficiency.

Relationships between soil characteristics, topography and plant diversity in a heterogeneous deciduous broad-leaved forest near Beijing, China

Patterns of biodiversity affect soil properties at different scales, conversely, soil characteristics and landscape features influence biodiversity. It is important to determine these relationships for understanding ecosystem processes. Many studies have carried out during the last few years mainly concentrated on factors that influence plant diversity in grassland or shrubland. Focused on the topography and forest heterogeneity for a warm temperate-zone deciduous broad-leaved forest in the Donglingshan Mountains near Beijing, detailed plant diversity, topography and soil features of 76 plots were investigated in a small watershed. To discern the complex relationships, multivariate statistical analysis techniques (Principal Component Analysis (PCA), Cluster Analysis (CA) and Canonical Correlation Analysis (CCA)) were employed. The results of PCA and CA showed that soil organic matter (SOM) is an important indicator to soil fertility. The coverage, richness and α-diversity index of three layers of plants (tree, shrub and herb) have unique features under different soil fertilities. High fertility plots often exist on south-facing slopes, in upper slope positions, and have gentle slope gradients. The coverage, richness and α-diversity index (Shannon index) of tree and shrub layers are the highest in mid-fertility plots, which have the highest available phosphorus (AP) and potassium (AK) contents, but those same summary descriptors for herbs are the least. CCA analysis elucidated the relationships of three different index groups (topography, soil and plant). Elevation and aspect have a close relationship with shrub richness and α-diversity. Elevation is also an important factor influencing SOM. SOM and total nitrogen have the greatest effect on plant characteristics (mainly shrub coverage) among all soil factors.

The effects of land-use combinations on soil erosion: a case study in the Loess Plateau of China

Land use is one of the key factors affecting soil erosion in the Loess Plateau of China. This paper examines soil erosion under different land uses and land-use combinations using 137 Cs tracing in the Yangjuangou Catchment, a tributary of the Yan River in the Loess Plateau of Northern Shaanxi Province. The results show that the order of 137Cs activity in different land uses decreases sequentially from mature forest to grass to young forest to orchard to terrace crop, indicating that the mature forests had the lowest erosion rates while the terraced cropland produced the highest erosion amount. The majority of 137Cs is distributed in the top 0—10 cm of the soil layer. The 137Cs activity in mature forest and grass soil is significantly higher than in other land uses. Three land-use combinations on the hillslope were selected to study the relationship between land-use combination and soil erosion. The mixtures of ‘grass (6 years old) + mature forest (25 years old) + grass (25 years old)’ and ‘grass (6 years old) + young forest (6 years old) + mature forest (25 years old) + grass (25 years old)’ are better for soil erosion control, lowering soil erosion amount by 42% compared with a land-use combination of ‘grass (6 years old) and shrub (6 years old)’. The results provide an important basis for optimizing land-use combinations to control soil erosion on slopes and may also result in important ecological benefits.

Double counting in ecosystem services valuation: causes and countermeasures

Many studies have been conducted on ecosystem services and double counting is a frequent problem that causes uncertainty and poor reliability of estimating the value of ecosystem services. By referring to previous studies of ecosystem service valuation, our research has identified the basic causes of double counting. These include ambiguous definitions and inconsistent classifications of ecosystem services, poor understanding of ecosystem complexity, inadequate recognition of exclusiveness and complementarities of individual ecosystem services, spatio-temporal scale dependence of ecosystem services, and overlap and lack of cross-referencing between ecosystem service valuation methods. Measures for reducing double counting in ecosystem service valuation are proposed as follow: (1) identifying the spatio-temporal scales of ecosystem services; (2) valuing the final benefits obtained from ecosystem services; (3) establishing consistent classification systems for ecosystem services; and (4) selecting valuation methods appropriate for the study context.