农牧交错带禁牧草地生态系统服务空间权衡与协同关系

为明确农牧交错带禁牧草地生态系统主要服务间的相互作用关系，以宁夏盐池县草地为研究对象，借助本地化的InVEST模型，对禁牧以来（2000－2015年）草地碳储存、水源涵养、土壤保持3项关键服务进行精准测度，明确其时空变化特征，以此为基础，通过逐像元相关系数法对3种服务间的权衡作用进行定量可视化表达，分析乡镇尺度各服务间的空间权衡与协同关系。结果表明：1）禁牧以来，草地生态系统碳储存、水源涵养和土壤保持功能显著增加，但增加过程存在一个显著的“N”型波动，碳储存总量及单位面积均值由217.46万t、5.78 t/hm2增加到263.12万t、6.19 t/hm2；水源涵养总量及单位面积均值由2 884万t、76.69 t/hm2增加到6 118万t、143.92 t/hm2；土壤保持总量及单位面积均值由1 383万t、36.78 t/hm2增加到3 474万t、81.71 t/hm2。碳储存功能与草地覆被关系密切，年际波动小、增长稳定，水源涵养和土壤保持功能受降水和地形显著影响，年际波动大、空间差异显著。2）草地土壤保持与水源涵养功能呈显著的空间协同关系（面积占86.34%），碳储存与水源涵养功能关系复杂，空间权衡与协同关系不显著（面积分别占47.66%和52.34%），碳储存与土壤保持功能呈空间协同关系（面积占69.55%）。通过定量可视化评估草地生态系统各服务间的空间权衡与协同关系，可为草地生态系统优化提供科学依据，为草地资源管理提供参考。

Spatial trade-offs and synergies of ecosystem services for grazing-prohibited grassland in agro-pasture ecotone

Sustainable management of landscapes determines the relationship between each ecosystem service on different spatial scales. Taking Yanchi County of Ningxia in China as the research area, this paper aims to clarify the interaction between the main ecosystem services of grazing-prohibited grassland in agro-pasture ecotone, using various techniques, such as data extraction of grassland, remote sensing inversion, and spatial analysis. After local correction to InVEST model, three key ecosystem services, including the carbon storage, the water conservation and soil conservation after grazing prohibition (2000a, 2004a, 2007a, 2010a, and 2015a), were measured to define the features of their spatial-temporal changes. The spatial trade-offs were represented quantitatively for three services, and the partial correlation analysis at a pixel scale was used to analyze the spatial synergies at the township scale. The results show that three indicators of grassland ecosystem, including the functions of carbon storage, water and soil conservation, were significantly enhanced since the grazing prohibition. Specifically, the total carbon storage and density increased from 2 174 600 tons and 5.78 t/hm2 to 2 631 200 tons and 6.19 t/hm2, respectively; the quantity and density of water conservation increased from 28.84 million tons and 76.69 t/hm2 to 61.18 million tons and 143.92 t/hm2, respectively; and the total quantity and density of soil conservation increased from 13.83 million tons and 36.78 t/hm2 to 34.74 million tons and 81.71 t/hm2, respectively. However, there was a significant "N" type fluctuation in the increasing process. During the whole period, the range of carbon storage in grassland ecosystem varied slowly with continuous increase or decrease; while the water and soil conservation showed a remarkable increase or decrease. In terms of regional differences, the increases of carbon storage and water conservation in the north were higher than that in the south, whereas, the increase of soil conservation in the south was higher than that in the north. The function of carbon storage was closely related to the grassland type, indicating small interannual fluctuation and stable growth. The water and soil conservation can depend significantly on precipitation and terrain, leading to large interannual fluctuations and significant spatial differences. There was a spatial synergistic relationship between the soil and water conservation (86.34%) of grassland. The relationship between carbon storage and water conservation was complex, where the spatial trade-off and synergetic relationship were not correlation (47.66% and 52.34% respectively), while the carbon storage and soil conservation showed a spatial synergistic relationship (69.55%). Terrains dominated the synergies and trade-offs relationship between the carbon storage and water conservation, as well the carbon storage and soil conservation. Specifically, the synergetic relationship in areas revealed a large topographic relief, while there was most trade-offs relationship in flat areas. Therefore, the quantitative visualization can be used to evaluate the spatial trade-offs and synergies among the services of grassland ecosystem. The proposed method can further provide a scientific basis for the optimization of the grassland ecosystem, and thereby serve as a sound support for the sustainable management of grassland resources.