Evolution and improvement options of ecological environmental quality in the world's largest emerging urban green heart as revealed by a new assessment framework

Abstract

Large ecological green spaces in cities are often designated as Urban Green Hearts (GHs) to support the ecological and recreational needs of urbanites. While GHs protection and sustainable development have been a high priority for urban planning and management, ecological environment quality (EEQ) of GHs has rarely been monitored and assessed. Here, we proposed a comprehensive assessment framework for EEQ based on entropy weights and rank-sum ratios methods, and applied the framework to the world's largest GH, Changsha-Zhuzhou-Xiangtan urban agglomeration Green Heart (CZT-GH), and its 5 km and 10 km buffer zones to examine the spatial-temporal dynamics of its EEQ from 2000 to 2019. Compared with the buffer zones, the EEQ in the CZT-GH was the best, with an annual average of 44.92 % of the area being High-grades EEQ. The restoration trend of EEQ was most conspicuous in only 8.4 % of CZT-GH, a small fraction compared with 25.1 % and 66.5 % of the CZT-GH showing deterioration trend and no change, respectively. Five factors were identified that calls for management attention: land use and cover change, spatial heterogeneity in vegetation restoration, temporal fluctuation in air quality improvement, comprehensive EEQ assessment and restoration, and capacity to cope with ecological risks. The approach, issues identified, and management measures proposed in this study should be applicable to GHs in general. The generic EEQ assessment framework and approaches developed in this study are generic and objective and therefore can be easily adapted to other regions; the procedures used to quantify the spatial and temporal changes of EEQ and identify underlying management issues provide essential information for formulating adaptive management measures of EEQ in general. SynopsisTaking the largest urban Green Heart as a case study, we established and applied a new general ecological environment quality (EEQ) evaluation system to monitor EEQ changes, identify issues, and propose management options.