Abstract: As China's economy and society step into a new normal state with the process of urban renewal, attention is increasingly shifting to the high-efficiency utilization of inventory resources. In this, green space construction is facing many challenges. In particular, the contradiction between residents' high demands for green space and the finite amount of available green space is becoming increasingly prominent in high-density cities. Thus, there is an urgent need to find an effective way to solve the contradiction between land scarcity and green space demand. Several studies have demonstrated that informal green land can be well adapted to the built environment in cities and can effectively solve several social and ecological problems in cities. As such, it has great development potential. However, research on informal green land is still in the exploration stage. Existing studies have mainly focused on the overall research framework; there is a lack of deep empirical research and discussion of specific implementation.
　　Based on the imbalance between the supply and demand of green space in cities, a case study of Gutai Central District in Fuzhou City was carried out. The supply and demand levels of green space in 13 control planning units of the study area were evaluated. Specifically, there were five evaluation indices of supply, including the park green space area ratio, park green space area per capita, park green space accessibility, landscape pattern index, and overlapping rate of park green space service area. There were two evaluation indices for demand, including dynamic population distribution and point-of-interest (POI) distribution. Following this evaluation, the green space balance level of each unit was judged by introducing locational entropy. Hence, the units with the most serious green space imbalance were identified and their informal green spaces were studied.
　　Unit 08 was chosen as the research sample. Through a field survey and screening, 76 informal green blocks that were viewed as imbalanced were identified. An evaluation system for informal green space updating potential was established to evaluate the updating potential of each site. With full consideration of the dynamic characteristics of informal green spaces, this study viewed time available potential and space available potential as the core decision variables in order to improve the public living environment quality in high-density old urban districts and the integration efficiency of informal green spaces. After evaluation of the time available potential and space available potential of each informal green space, the updating potentials of different sites were finally assessed by introducing the Pareto optimal solution set. The non-dominated sorting genetic algorithm (NSGA-II) was employed in Matlab for these calculations. The prior levels of several solution sets for the renewal and reconstruction of informal green space in the study area were solved, thus obtaining an updated time sequence of informal green spaces. Further, the green space supply-demand matching condition of imbalanced units was recalculated after adding in the informal green space with the highest potential. The findings verified that the renewal of informal green spaces can relieve supply-demand imbalances in urban green spaces and further meet residents' demands for green spaces. 
　　Finally, three renewal strategies for informal green spaces were proposed, including grouped construction and gradual implementation; adjusting measures to local conditions by adopting strengths and avoiding shortages; and building a governance platform and carefully implementing paths. For the three types of informal green spaces, the development directions for the various fields and paths for the renewal and utilization of informal green spaces were discussed. These research results provide a reference for the renewal and development of green spaces in high-density old urban districts.

Key words: supply-demand imbalance, informal green space, Pareto optimal solution set, renewal strategy

摘要： 我国经济社会发展步入新常态，城市发展开启存量更新模式。居民绿地需求与绿地空间不足之间的矛盾日益凸显，已有研究证明，非正式绿地在城市建成环境中具有良好适应性，能够有效解决城市面临的一系列社会和生态问题，具备较大发展潜力。聚焦于绿地低供高需的城市区域，以福州市鼓台中心区为例，通过实地调研挖掘供需失衡区范围内可利用的非正式绿地资源。从时、空间可用潜力两个维度确定影响非正式绿地发展潜力的评价指标，建立多目标优化模型；引入帕累托前沿理论，利用Matlab中非支配排序遗传算法求解得出调研区域内对非正式绿地进行更新改造的多个解集的优先层级。最后基于综合评估结果和三种不同的场地类型提出非正式绿地的更新策略，为高密度老旧城区绿地的存量更新发展提供借鉴。

关键词: 供需失衡, 非正式绿地, 帕累托最优解集, 更新策略