Objective The construction of high-carbon-sequestration urban green space has become a key component of high-quality built environment development under the carbon neutrality strategy. Systematic quantitative analysis and digital mapping of carbon sequestration efficiency provide essential scientific and practical guidance for enhancing urban green space quality and ecological resource management. As a primary natural carbon sink, urban green space mitigates carbon emissions and improves human settlement quality. Carbon sequestration efficiency—per unit time or area—captures the spatio-temporal dynamics of carbon sequestration and serves as an integrated indicator for evaluating multi-path carbon cycle performance in landscape green spaces. Rapid urbanization and fragmented, heterogeneous green space patterns increasingly constrain urban carbon sequestration. Therefore, quantitative assessment of carbon sequestration efficiency is crucial for identifying enhancement strategies. However, traditional measurement methods often suffer from unstructured consideration of carbon paths, incomplete analytical frameworks, low accuracy, and unclear strategy guidance, highlighting the urgent need for landscape architecture oriented, layered carbon sequestration path based, fine grained, quantitative approaches to improve reliability, validity, and spatial precision in carbon sequestration analysis and visualization.

Methods Grounded in urban green space development and layered carbon sequestration principles, this study establishes a quantitative framework for evaluating urban green space carbon sequestration efficiency and integrates the layered carbon sequestration path method into measurement modeling. The framework is applied to the Yanziji Blocks, Nanjing, under both original and redevelopment conditions. The workflow includes: 1) constructing the carbon sequestration efficiency analysis system; 2) identifying and classifying urban green spaces; 3) layered sampling and field surveys; 4) efficiency measurement using the layered carbon sequestration path algorithm; and 5) digital mapping and spatial analysis. Carbon sequestration mechanisms—including carbon fixation, biomass accumulation, soil carbon storage, litter decomposition, and rhizosphere cycling—were examined to guide model development. Landscape green spaces were extracted and categorized based on carbon sequestration characteristics, forming hierarchical geospatial datasets. Layered sampling plots for vegetation, soil, and micro-habitats, supplemented by literature data, created a comprehensive plot database. Carbon sequestration coefficients were calculated using layered path formulas and combined with terrain and vegetation data to construct efficiency measurement models, supporting multi-dimensional spatial analysis. Using Yanziji Blocks as a case, grid-based spatial quantification, visual mapping, and statistical evaluation were conducted, focusing on composition, spatial distribution, contribution proportion, improvement potential, and hotspot identification.

Results The empirical results indicate the following three aspects: 1) The layered-path-based carbon sequestration efficiency measurement model demonstrates strong applicability for urban block-scale analysis. It enables accurate quantification of carbon sequestration characteristic coefficients, total carbon sequestration, and multi-dimensional carbon sequestration efficiency under both the original conditions and the redevelopment plan. 2) Comparative digital mapping showed that the redevelopment plan substantially improved overall carbon sequestration efficiency relative to the original conditions, transforming the spatial pattern from an uneven distribution into a more balanced and optimized one. Multiple hotspot regions emerged, reflecting enhanced spatial clustering of high-efficiency areas. Meanwhile, carbon sequestration improvement potential decreased significantly and tended toward theoretical saturation, suggesting that the redevelopment plan achieved nearly optimal carbon sequestration levels. 3) The results further demonstrate that reasonable planning—such as increasing the green space ratio, optimizing vegetation structure through multi-layered canopy configuration (tree−shrub−groundcover), and integrating vertical greening (e.g., roof gardens)—effectively enhances carbon sequestration efficiency under new urban development scenarios.

Conclusion This study establishes a layered-path-based carbon sequestration efficiency analysis system, develops a fine-scale measurement model, and implements a digital mapping toolkit for urban green space carbon sequestration efficiency at the urban block scale. The proposed approach effectively addresses the limitations of low measurement accuracy, incomplete analytical frameworks, and insufficient spatial representation in current research. It significantly improves the reliability and validity of carbon sequestration efficiency quantification and visualization. The findings provide theoretical foundations, methodological guidance, and technical support for the organic renewal and redevelopment of the built environment under carbon neutrality objectives, and offer a replicable framework for the planning, evaluation, and design of high-carbon-sequestration urban green spaces.