降水梯度下集水区尺度生态系统服务权衡与协同研究——以黄土高原中部为例

On the Loess Plateau, the ecosystem services (ESs) are undergoing significant change, where soil conservation service of local ecosystems was enhanced but water yield and crop production were decreased. Although the relationships among ESs were already discovered and explained in this region, change of such relationships along the precipitation gradient was yet to be revealed and proved, and also the approach for managing trade-offs of ESs was not presented before. The proposed study will focus on several catchments along the precipitation gradient across the central Loess Plateau. The geographic database will be constructed by data collection, image interpretation and field survey. ESs related to crop production, water yield and soil conservation will be estimated by GIS and InVEST model before and after Grain for Green Project. Trade-offs among ESs will be quantified at integral catchment and grid cell level respectively, by introducing a novel quantitative method. The differentiation of such trade-offs and synergies at integral catchment level along the precipitation gradient will be clarified. A relation function between such trade-offs and vegetation coverage will be established. The spatial pattern of such trade-offs will be analyzed to identify the key areas where trade-offs among ESs are severe by hotpot analysis. Therefore, a regulation scheme for trade-offs among ESs will be proposed based on vegetation coverage adjustment in different precipitation zone. This study will contribute to the theories related to trade-offs and synergies among ESs, and will develop an effective method for scientific management of ESs.

黄土高原生态系统服务经历着深刻变化，土壤保持服务增强的同时却面临着粮食与淡水供给服务减弱。目前，三者之间权衡或协同关系已经明确，但其沿降水梯度的分异规律尚不清楚，生态系统服务权衡管理尚缺乏有效途径。本研究针对黄土高原中部不同降水梯度带的集水区，通过资料收集、遥感解译与野外调查建立研究区地理数据集；基于GIS与InVEST模型对研究区退耕还林前后土壤保持、粮食与淡水供给服务进行评估；引入定量化方法，在集水区整体与栅格水平上量化生态系统服务权衡与协同强度；厘清集水区整体生态系统服务权衡与协同关系沿降水梯度分异规律；分析集水区内权衡与协同的空间格局，构建权衡对植被覆盖的响应关系函数；通过热点分析识别生态系统服务权衡的重点区域，针对不同降水梯度带，提出基于植被覆盖调整的生态系统服务权衡调控方案。本研究有助于生态系统服务权衡与协同理论的深化，期望为生态系统服务科学管理提供有效途径。

退耕还林（草）工程使黄土高原土壤保持与碳储量增加但产水量与土壤含水量下降，如何协调不同降水区域生态系统服务关系是重要的科学问题。本项目针对产水量、土壤保持、碳储量等典型生态系统服务，以野外实测与InVEST模型评估为手段，开展了如下研究：（1）集水区整体生态系统服务权衡与协同关系沿降水梯度分异规律；（2）样地生态系统服务权衡及其影响因素；（3）集水区内生态系统服务权衡与协同空间格局；（4）生态系统服务权衡重点区域识别与调控。本项目主要取得如下认识：（1）土壤保持、产水量与碳储量均表现为随降水量降低而降低，植被覆盖是生态系统服务变化的主要原因；三个降水区域生态系统服务均表现为倾向于土壤保持与碳储量的趋势；针对不同降水区域提出了不同植被类型配置比例的建议。（2）土壤保持与土壤水分权衡的主控因素为植被类型、粉粒与砂粒含量，其次为海拔、坡度与坡位，天然草地、人工草地、沙棘能够降低生态系统服务权衡强度；植被碳储量与土壤水分权衡的主控因素是植被盖度与植被类型，其中柠条与沙棘权衡强度最低。综合来看，沙棘是较好的植被恢复物种。（3）安塞集水区土壤保持与产水服务权衡、碳储量与产水服务权衡表现为从东南到西北逐渐降低。（4）土壤保持与产水服务权衡的主控因素是坡度与草地比例；增加草地能够抑制权衡。碳储量与产水服务权衡的主控因素是乔木林地与草地比例、植被盖度与土壤有机质含量；权衡强度与主控因素为二次函数关系，前3项主控因素占比分别控制在22%、59%、52%，能够实现权衡最小化。重点调控土壤干燥化与高权衡强度区域，建议生态恢复模式为：以集中连片草地为基质，在其中镶嵌面积较小但多边缘的乔木林斑块，耕地不再做大规模调整。