Wenwu Zhao

Ecosystem service trade-offs and their influencing factors: A case study in the Loess Plateau of China

Soil erosion control (SEC), carbon sequestration (CAS), and soil moisture (SMO) strongly interact in the semi-arid Loess Plateau. Since SMO has supportive effects on SEC and CAS, it can be considered as ecosystem service (ES), and there is an immediate need to coordinate the relationships among these ecosystem services (ESs) to promote the sustainability of vegetation recovery. In this study, we quantified the ESs, ES trade-offs, and the environmental factors in 151 sample plots in the Ansai watershed, and we used a redundancy analysis (RDA) to clarify the effects of environmental factors on these ESs and their trade-offs. The results were as follows: (1) the general trend in the SEC of vegetation types was Robinia pseudoacacia (CH)>native grass (NG)>small arbor (ST)>Hippophae rhamnoides (SJ)>artificial grass (AG)>Caragana korshinskii (NT)>apple orchard (GY)>crop (CP); the CAS trend was CH>SJ>NT>AG>CP>ST>GY>NG; and the SMO trend was CP>NG>GY>AG>SJ>ST>CH>NT. (2) For SEC-SMO trade-offs, the influence of vegetation type, altitude, silt and sand composition was dominant. The arrangement of NG, AG, and SJ could decrease the extent of the trade-offs. (3) For CAS-SMO trade-offs, vegetation coverage and types were the dominant factors, but the effects were not complex. The extent of these trade-offs was lowest for NT, and that for SJ was the second lowest. (4) Considering the relationships among the three ESs, SJ was the most appropriate afforestation plant. Combing the vegetation types, slope position, slope gradient, and soil properties could regulate these ES relationships. The dominant factors influencing ES trade-offs varied among the different soil layers, so we must consider the corresponding influencing factors to regulate ESs. Moreover, manual management measures were also important for coordinating the ES relationships. Our research provides a better understanding of the mechanisms influencing the relationships among ESs.

Landscape service capability, landscape service flow and landscape service demand: A new framework for landscape services and its use for landscape sustainability assessment

Creating methods to achieve sustainable development is a global challenge faced by civilization in the 21st century. As an operational element of sustainability science, landscape sustainability science (LSS) plays an important role in the development of methods for sustainable development. Landscape services (LS) is a newly emerging concept associated with ecosystem services (ES) that exhibits great potential for promoting landscape sustainability research despite its nascent stage of development. In this article, the historical development of the LS concept is reviewed, and the special implications and advantages of LS relative to ES for landscape practices are further expanded. Furthermore, a sustainability-oriented LS conceptual framework specifically developed for the integration of LS and landscape sustainability research is proposed. We refer to this framework as the landscape service capability-flow-demand (LSCFD) framework. Finally, the prospects for the application of the new framework in landscape sustainability assessments are explored. By using LSCFD, we suggest that a distinction be made between landscape service capacity (LSC), landscape service flow (LSF), and landscape service demand (LSD). LSC refers to the long-term potential of a landscape for producing various types of materials, energy, information, conditions, and effectiveness that are valued by people. LSF refers to the transmission process for material, energy, information, conditions and effectiveness from a landscape to benefit people that occur either within or across the landscape. LSD is the societal dimension of LS and refers to the types and volume of material, energy, information, conditions, and effectiveness that a landscape’s inhabitants need to satisfy their existence, livelihood, and development. Based on the LSCFD framework, landscape sustainability assessments can be performed by considering the following four areas: LSC sustainability, LSF sustainability, LSD sustainability, and the dynamic equilibrium relationships among the other three areas. Thus, various types of LS capabilities, integrated services capabilities, and the diversity and balance of LS demands should be evaluated. Additionally, analyzing the supplying regions of LS flow, spatial orientation of the population that benefits, transmission media, transmission mechanism, and transmission limiting factors is essential to explore the dynamic equilibrium relationships between LS capability, flow, and demand. The LSCFD concept framework of LS provides a method for implementing LSS into actual practice. In the context of global environmental changes and sustainable development, the LSCFD framework of LS will definitely contribute to future research.

Driving forces and their contribution to the recent decrease in sediment flux to ocean of major rivers in China

Understanding the mechanisms behind land-ocean sediment transport processes is crucial, due to the resulting impacts on the sustainable management of water and soil resources. This study investigated temporal trends and historical phases of sediment flux delivered to the sea by nine major rivers in China, while also quantifying the contribution of key anthropogenic and natural driving forces. During the past six decades, sediment flux from these nine major rivers exhibited a statistically significant negative trend, decreasing from 1.92Gtyr-1 during 1954-1968 to 1.39Gtyr-1, 0.861Gtyr-1 and 0.335Gtyr-1 during 1969-1985, 1986-1999 and 2000-2016, respectively. We used a recently developed Sediment Identity approach and found that the sharp decrease in sediment load observed across China was mainly (~95%) caused by a reduction in sediment concentration. Reservoir construction exerted the strongest influence on land-ocean sediment fluxes, while soil conservation measures represented a secondary driver. Before 1999, soil erosion was not controlled effectively in China and reservoirs, especially large ones, played a dominant role in reducing riverine sediments. After 1999, soil erosion has gradually been brought under control across China, so that conservation measures directly accounted for ~40% of the observed decrease in riverine sediments. With intensifying human activities, it is predicted that the total sediment flux delivered to the sea by the nine major rivers will continue to decrease in the coming decades, although at a slower rate, resulting in severe challenges for the sustainable management of drainage basins and river deltas.

Influence of land use change on the ecosystem service trade-offs in the ecological restoration area: Dynamics and scenarios in the Yanhe watershed, China

Land use change can result in variations in ecosystem services (ESs) and their relationships. Studying the temporal dynamics of ESs and their relationships can support scenario analyses that provide the theoretical basis for policy decisions and regional ecosystem management. Previous studies have revealed the trade-offs between two ESs on multiple scales, while the trade-offs between multiple ESs require further analysis. Furthermore, trade-offs are rarely considered in scenario constructions, which weakens the ability of scenarios to inform land use policy. In this study, the InVEST model was applied to assess carbon sequestration, habitat quality, nutrient retention, sediment retention and seasonal water yield at five-year intervals from 1990 to 2015 and to construct five simulated scenarios that represented different ecological restoration and land reclamation policies. The results indicated that the Grain for Green Project (GFGP) increased all ESs, with seasonal water yield increasing by approximately 1.29 times above the initial stage. However, decreasing cropland area reduced the correlations between ESs both in trade-offs and synergies. Among all scenarios studied, the Returning Cropland to Grassland trade-off scenario had the maximum effect, while the natural succession to shrubland scenario had a minimum effect at the pixel level. Except for the land reclamation scenario, the overall ES benefits in the other scenarios exceeded the benefits received in 2015. Given the extent of watershed areas impacted by different overall ES benefit and trade-off situations, the Returning Cropland to Grassland scenario appears to best reduce the impacts of the worst situation compared to 2015, reducing the negative impacts by 22.6%. We suggest that scenarios that combine both overall ESs values and their trade-offs can support more effective and efficient land use decisions.

Deviation of land-use data from quickbird and TM remote sensing imagery: A case study of the Tanjiaying small watershed in the loess hilly-gully area of China

Land-use maps provide important data and basic information for accomplishing the optimal allocation of resources and for ensuring sustainable development. However, the land-use data interpreted from various sources of remotely sensed, low-resolution imagery are highly variable. Therefore, an analysis of these deviations in land-use data is imperative for correcting the accuracy of the land-use maps derived from such low-resolution, remote sensing imagery. With ArcGIS 9.3 software, we derived the land-use maps with different accuracies for the Tanjiaying small watershed in the loess hilly-gully area of China by interpreting Landsat 5 Thematic Mapper (TM) and QuickBird images acquired in 2010. We compared the maps derived from these two sources of imagery data and analyzed the resulting deviation distribution with respect to the slope, aspect, and elevation of the land.

Evaluating the use of fire to control shrub encroachment in global drylands: A synthesis based on ecosystem service perspective

With the proliferation of woody plant species in much of the worlds grasslands, human has manipulated landscape fire to return their forage provisioning service. Yet other ecosystem services (e.g., carbon sequestration, biodiversity conservation, erosion control) in the post-managed areas compared to those previously available in the shrub-encroached area are largely unknown, including trade-offs between ecosystem services. Using data from previous publications, we quantitatively synthesized the sustainability of fire as shrub management practice, expressed as its efficacy to control shrubs and its capacity to maintain different ecosystem services. A simple indicator (δ), defined as the ratio of an observed ecological attribute between area experiencing shrub management and untreated control, was used to quantify the changes. Our results showed that fire could be an effective strategy to control shrubs and to increase forage provisioning service (δherbaceous biomass = 1.39). However, there are possible trade-offs with other ecosystem services (e.g., erosion control, nutrient cycling) when a 54% increase in bare soil cover (δbare soil = 1.54) and ~74% loss of biological soil crusts cover (δbiological crust = 0.26) were found. Because increasing forage provisioning at the cost of other ecosystem services might not be sustainable, management should focus on strategies to minimize such trade-offs, which may include but not limited to rotational grazing, adjustment in stocking rate, or supplementary external inputs (e.g., fertilizer). Unless those measures are employed, there is possible emergence of a novel crash (i.e., vegetation- and resource-poor scabland) resulting from a combination of soil erosion and high vulnerability of burnt landscape to exotic species invasion.

Effects of reforestation on plant species diversity on the Loess Plateau of China: A case study in Danangou catchment

Large-scale vegetation restoration has important impacts on plant species diversity, which then influences plant community stability and resilience. The purpose of this paper is to compare the diversity of plantations as well as the diversity of artificially restored and naturally restored grasslands under different years of recovery and to identify the plots with the highest species diversity by vegetation type and restoration duration to determine strategies for vegetation restoration in hilly and gully regions of the Loess Plateau. Stands of Robinia pseudoacacia and Caragana korshinskii of different ages (10, 20, 30 and 40 years old) in the Danangou catchment on the Loess Plateau of China were selected as a case study to analysis effects of afforestation on the structure and function of ecosystems. The results showed that (1) under different numbers of years of recovery, the species diversity of woodland changes with changes in the coverage of woody plants, and the species diversity of R. pseudoacacia plantations planted on sunny slopes and R. pseudoacacia and C. korshinskii plantations planted on shady slopes reaches its maximum when coverage reaches a minimum value after 20 and 30 years of recovery, respectively; (2) soil moisture (in both shallow and deep layers) is the key factor controlling species diversity in woodlands, as the soil moisture changes with the coverage of woody plants following different numbers of years of recovery, which then influences the species diversity; (3) compared to the woodlands, the natural grassland exhibited higher species diversity under all recovery duration. Therefore, natural recovery is recommended if only species diversity is considered rather than human demand for wood, but if demand for materials is considered, we recommend thinning R. pseudoacacia on sunny and shady slopes at the ages of 10-20 and 10-30 years, respectively.

Relationship between soil water content and soil particle size on typical slopes of the Loess Plateau during a drought year

In the context of global climate change as well as local climate warming and drying on the Loess Plateau of China, understanding the relationship between soil particle size and soil water distribution during years of atypical precipitation is important. In this study, fractal geometry theory is used to describe the mechanical composition and texture of soils to improve our understanding of hydropedology and ecohydrology in the critical zone on the Loess Plateau. One grassland slope and two shrubland slopes were selected in the hilly and gully region of the Loess Plateau, and soils were sampled along hillslope transects at depths of 0-500 cm. Fractal theory and redundancy analysis (RDA) were used to identify relationships between the fractal dimension of soil particle-size distributions and the corresponding van Genuchten parameters for the soil-water-characteristic curves. The oven-drying method was used to measure soil water content, and the high-speed centrifugation method was used to generate soil-water-characteristic curves. The results show that (1) the soil water that can be used by Caragana korshinskii during a drought year is distributed below 2 m from the surface, whereas the soil water that can be used by grass is below 1.2 m; (2) Caragana korshinskii promotes the conservation of fine soil particles more than does natural restored grass, and the soil particle-size distribution fractal dimension changes with depth and position; and (3) soil hydraulic properties correlate strongly with soil pedological properties such as bulk density and the soil particle-size distribution fractal dimension. These results provide a case study of the relationships among soil distributions, hydrologic and geomorphic processes for vegetation restoration in drylands with a thick vadose zone. More studies on soil property changes are needed to provide case studies and empirical support for ecological restoration in the Loess Plateau of China.

Distribution of Shrubland and Grassland Soil Erodibility on the Loess Plateau

Soil erosion is one of the most severe problems facing environments and has increased throughout the 20th century. Soil erodibility (K-factor) is one of the important indicators of land degradation, and many models have been used to estimate K values. Although soil erodibility has been estimated, the comparison of different models and their usage at a regional scale and, in particular, for different land use types, need more research. Four of the most widely distributed land use types were selected to analyze, including introduced and natural grassland, as well as introduced and natural shrubland. Soil particle size, soil organic matter and other relevant soil properties were measured to estimate soil erodibility in the Loess Plateau. The results show that: (1) the erosion productivity impact calculator (EPIC) model and SHIRAZI model are both suitable for the Loess Plateau, while the SHIRAZI model has the advantage of fewer parameters; (2) introduced grassland has better ability to protect both the 0–5 cm soils and 5–20 cm soils, while the differences between introduced and natural shrubland are not obvious at a catchment scale; (3) the K values of introduced grassland, natural grassland, introduced shrubland and natural shrubland in the 0–5 cm layer vary from 0.008 to 0.037, 0.031 to 0.046, 0.012 to 0.041 and 0.008 to 0.045 (t·hm2·h/(MJ·mm·hm2)), while the values vary from 0.009 to 0.039, 0.032 to 0.046, 0.012 to 0.042 and 0.008 to 0.048 (t·hm2·h/(MJ·mm·hm2)) in the 5–20 cm layer. The areas with a mean multiyear precipitation of 370–440 mm are the most important places for vegetation restoration construction management at a regional scale. A comprehensive balance between water conservation and soil conservation is needed and important when selecting the species used to vegetation restoration. This study provides suggestions for ecological restoration and provides a case study for the estimate of soil erodibility in arid and semiarid areas.