关中平原城市群扩张对生态用地的多尺度影响

城市扩张与生态空间保护的矛盾是新型城镇化和国土空间规划过程中急需解决的问题之一。作为黄河流域生态保护与高质量发展的核心区域，关中平原城市群面临更加严峻的生态和资源胁迫。但相关研究主要对研究区整体的生态环境变化进行测度，少有研究分析城市群发展对生态用地的多尺度影响，且忽略了城市群中土地变化最剧烈，生态受胁迫最严重的城市边缘区。因此，基于土地利用数据，结合土地利用转移矩阵、景观指数、估算城市扩张间接影响的生态用地面积等方法，研究从城市群、重点城市和主要城市边缘区3个尺度分析1990-2018年城镇扩张对生态用地的直接和间接影响。结果表明：（1）关中平原城市群土地利用类型以半生态用地（耕地）为主，面积占比超过40%。而城市边缘区主要以半生态用地和建设用地为主。1990-2018年城市群建设用地面积比例由3.67%增长至5.93%，耕地面积共计减少3032.11 km²，自然生态用地的面积增加628.03 km²。受耕地占补、退耕还林等多重政策的影响，半生态用地和自然生态用地的变化呈现为"拉锯式"发展特征。（2）城市扩张对半生态用地的直接影响大于对自然生态用地的直接影响，各尺度土地利用转移变化大同小异，新增建设用地的主要来源均为耕地，其中城市边缘区的耕地受城镇扩张的挤占最为突出。（3）城市扩张对自然生态用地的间接影响大于直接影响，且不同城市建设用地对自然生态用地的间接影响因耕地补偿机制的不同而有所差异。因此，对关中平原城市群实施"一刀切"的耕地补偿政策实际上并不合理，应当因地制宜，考虑地区土地资源条件，适当调整发展和约束政策，更有利于城市群的可持续发展。

The multi-scale direct and indirect effects of urban expansion of Guanzhong Plain Urban Agglomeration on ecological land

The contradiction between urban expansion and ecological spatial protection is one of the urgent problems to be solved in the process of new urbanization and national territory spatial planning. As the core area for ecological protection and high-quality development in the Yellow River Basin, the Guanzhong Plain Urban Agglomeration is facing more severe ecological and resource stresses. However, relevant studies have mainly measured the ecological changes in the study area as a whole, and few studies have analyzed the multi-scale impacts of urban agglomeration development on ecological land, and neglected the urban fringe areas in urban agglomerations with the most drastic land changes and the most severe ecological stresses. Therefore, based on the land use data, combined with the land use transfer matrix, landscape index, and methods to estimate the area of ecological land indirectly affected by urban expansion, this article selects three scales (urban agglomerations, prefecture-level cities, and urban fringe areas) to analyze the direct and indirect impacts of urban expansion on ecological land from 1990 to 2018. The results show that:(1) the land use type of the urban agglomeration in the Guanzhong Plain is dominated by semi-ecological land (farmland), with an area accounting for more than 40%. The urban fringe areas are mainly semi-ecological land and built-up land. The proportion of built-up land in urban agglomerations increased from 3.67% in 1990 to 5.93% in 2018. The area of farmland decreased by 3,032.11 km², while the area of natural ecological land increased by 628.03 km². Affected by multiple policies such as the requisition-compensation balance of farmland and grain for green, the semi-ecological land and natural ecological land compensate for each other. (2) The direct impact of urban expansion on semi-ecological land is greater than that on natural ecological land, and the changes in land use transfer are similar at all scales, with the main source of new built-up land being farmland. The farmland in urban fringe areas is most prominently occupied by built-up land. (3) The indirect impact of urban expansion on the natural ecological land is greater than the direct impact and the indirect impact is different due to the different compensation mechanisms for farmland. Therefore, it is unreasonable to implement a unified farmland compensation policy for the urban agglomeration. It is necessary to consider the regional land resource and conditions and appropriately adjust the development and restraint policies, which is conducive to the sustainable development of the urban agglomeration.