Construction and application of comprehensive evaluation system for urban green space garden plants based on group decision-making and analytic hierarchy process: a case study of Chengdu main urban area

Carrying out the evaluation of urban green space plants, scientifically and rationally selecting garden plants to enable them to give full play to their multiple functions and benefits such as ecology, society, and landscape, is of great significance to the construction of urban ecological civilization. How to select more comprehensive evaluation indicators and construct a comprehensive evaluation system for urban green space plants is particularly necessary. This study proposed a set of methods for indicator screening and comprehensive evaluation system construction, and applied them to 290 species of green space garden plants in 5 main urban districts of Chengdu (including 116 arbor species, 88 shrub species (including vines), and 86 herb species (including bamboos)). The results were as follows: (1) In terms of indicator selection, this study first preliminarily selected 6 criteria (biological characteristics, landscape value, ecological function, ecological adaptability, cultural and economic functions, afforestation and management costs) and 50 indicators through literature review, expert consultation, and the "brainstorming method". Then, 20 experts were invited to screen the preliminary indicators through three rounds of the Delphi method, and finally 35 indicators were selected to construct the evaluation indicator system for urban green space garden plants. (2) For the construction of the comprehensive evaluation model, this study adopt a combination of group decision-making and analytic hierarchy process (AHP). ① 18 experts were invited to score the importance of the 6 criteria layers and 35 indicators respectively. The AHP was used to construct judgment matrices, and the individual weight of each expert was calculated. ② The individual weights of experts were taken as the standard for systematic clustering, and the weight coefficients were calculated according to the number of experts in the category where different experts belong. The individual weights were linearly weighted with the expert weight coefficients to obtain the group weights of the evaluation objects. ③ Based on relevant research and expert consultation results, a 1-5 point graded evaluation standard was established for each indicator. According to the graded evaluation standards, the score of each indicator for each evaluated object was obtained by consulting relevant references and seeking expert opinions. Finally, the group weights and the scores of the evaluation objects were weighted and summed to obtain the comprehensive evaluation score of the evaluation objects. (3) The evaluation results of green space garden plants in the 5 main urban districts of Chengdu were as follows: among arbors, 52.59% had a comprehensive score of 3.5 or above; among shrubs (including vines), 68.18% had a comprehensive score of 3.0 or above; among herbs (including bamboos), 80.23% had a comprehensive score of 2.8 or above. The comprehensive evaluation scores of the 5 main urban districts ranged from 70.48 to 71.04 points, indicating that the application of green space garden plants in Chengdu was at an above-average level. The results of this study can provide methodological reference for the construction of a comprehensive evaluation system for urban green space plants, and also offer scientific basis and practical reference for the selection of garden plants and the construction of landscape in the process of building "Park City Demonstration Zone" in Chengdu.