黄土高原土地利用变化的生态环境效应

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

黄土高原是典型的生态脆弱区,随着我国退耕还林还草等一系列生态恢复和治理工程的开展,土地利用发生巨大变化.格局-过程-服务综合研究方法为理解土地利用变化的生态环境效应、科学指导生态恢复实践提供了途径.相关研究系统阐明了黄土高原土地利用格局对土壤水分、养分和土壤侵蚀过程的影响;揭示了植被恢复过程中固碳与产水服务的权衡关系及其时空变异规律,发现目前植被恢复已接近区域水资源承载力阈值;研发了区域生态系统服务综合评估与优化模型系统,提出了土地利用优化配置方案.上述成果推动自然地理学从定性结构分析向定量过程研究发展,引领生态系统服务研究深入到过程机制和综合集成,为黄土高原生态恢复提供了关键科学依据.

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 60 years.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.