Ecological and environmental effects of land-use changes in the Loess Plateau of China

Abstract

<p indent="0mm">The Loess Plateau (LP) is a typical ecologically fragile area in China, with severe water shortage and soil erosion. Understanding the interactions between land use structure and ecological processes is the basis for effective soil and water conservation. Since the implementation of large-scale vegetation restoration programs, changes in carbon and water services, as well as trade-offs in these services have become a new scientific challenge in this region. A comprehensive analytical paradigm of “pattern–process–service” was developed by our research group to determine the ecological and environmental effects of land-use changes and support ecological restoration practices. First, by combining landscape pattern, ecological process, and scale, we studied the effects of land-use changes on soil moisture, nutrients, and erosion at multiple spatial scales of plot, transect, catchment, and region, and illustrated the mechanisms of the interactions between land-use structure and ecological processes in the LP systematically. These works have revealed the relationships among ecosystem structure, land-use structure, vegetation functional traits, vegetation biomass, ecological processes (e.g., hydrological processes and nutrient cycling) and ecosystem services. They have also identified the key roles of soil water content and understory plant diversity in ecosystem service maintenance in dryland ecosystems. Second, by linking ecological processes and ecosystem services, we studied the formation and interaction mechanisms of ecosystem services. A sediment attribution diagnostic method focusing on soil retention services was developed to diagnose the contributions of multiple factors to changes in the sediment loads of rivers. Application of this method quantitatively revealed the drivers (climate change, vegetation restoration, and ecological engineering) and mechanisms underlying the drastic reduction in the sediment load of the Yellow River over the past <sc>60 years.</sc> The trade-off between carbon sequestration and water yield was quantitatively revealed, and its temporal and spatial variations during vegetation restoration were detected. The threshold of forest restoration potential within the limit of annual precipitation, as well as the turning point from soil carbon source to soil carbon sink following farmland abandonment, was identified. By considering water consumption for both vegetation growth and socioeconomic uses, a quantitative coupling analysis framework for the sustainable use of water resources in the natural–social–economic system of the LP was constructed, and regional water-resource carrying capacities for vegetation restoration in the region under various scenarios were determined; the results suggest that current vegetation restoration is approaching sustainable water resource limits. Third, on the basis of an understanding of the relationships between ecosystem processes and services at multiple scales, a spatially explicit assessment and optimization tool for regional ecosystem services was developed to reveal the spatiotemporal dynamics of ecosystem services on the LP, including water yield, soil retention, carbon sequestration, and grain production. By combining scenario analysis and ecosystem service quantification models with a spatial optimization algorithm, this new decision-supporting tool is capable of spatially optimizing multiple ecosystem services. This has contributed crucially to the advancement of integrated research into regional ecosystem services with the aim of quantifying, modeling, and supporting the rational planning and effective implementation of ecological projects. These findings have promoted the development of physical geography from qualitative structure description to quantitative process research. They have also led ecosystem services research into ecological processes and mechanisms and their comprehensive integration and have provided a key scientific basis for ecological restoration of the LP.