Evaluation of Carbon Storage and Carbon Sequestration Functions of Urban Street Trees: A Case Study of Jinju City

Background and objective: Urban street trees contribute to climate change mitigation by storing carbon in biomass and sequestering atmospheric CO₂ through growth. However, quantitative assessments of carbon storage and annual carbon uptake by street trees are still limited in many Korean cities. This study evaluated the carbon storage and carbon sequestration functions of street trees in Jinju City, South Korea, and examined how these functions differed according to district-level tree structure, species composition, and mean diameter at breast height (DBH).Methods: Street-tree inventory data for Jinju City were obtained from a public dataset and reorganized into 10 districts (A–J). Trees were classified into needleleaf and broadleaf groups, and carbon storage and annual carbon uptake were estimated using DBH-based coefficients derived from existing urban tree carbon estimation equations. District-level comparisons were conducted for tree abundance, mean DBH, total carbon storage, annual carbon uptake, and the relationship among broadleaf proportion, mean DBH, and mean CO₂ uptake per tree.Results: Tree structure and carbon functions differed markedly among districts. Total carbon storage was highest in district H (1,605 tCO₂), indicating that mature stands with large DBH acted as major carbon reservoirs. In contrast, annual carbon uptake was greatest in district C (68.5 tCO₂ yr⁻¹), suggesting that districts dominated by younger and actively growing trees can contribute more strongly to current carbon sequestration. Under the functional-group-specific equations applied in this study, broadleaf trees generally showed higher model-estimated carbon storage and annual carbon uptake per tree than needleleaf trees in mixed-tree districts. Broadleaf trees exhibited carbon storage of 242.14–1458.40 kg CO₂ tree⁻¹ and annual carbon uptake of 21.14–47.42 kg CO₂ tree⁻¹ yr⁻¹, whereas needleleaf trees showed 92.08–438.14 kg CO₂ tree⁻¹ and 3.87–6.54 kg CO₂ tree⁻¹ yr⁻¹, respectively. In addition, descriptive comparisons showed differences in model-estimated mean CO₂ uptake per tree according to district-level broadleaf proportion and mean DBH.Conclusion: The carbon storage and sequestration functions of street trees in Jinju City were strongly influenced by district-level tree structure, species composition, and mean DBH. Mature tree-dominated districts contributed more to total carbon storage, whereas districts with higher broadleaf representation and active growth contributed more to annual carbon uptake. These findings suggest that future street-tree management should move beyond conventional landscape maintenance and adopt carbon-oriented strategies, including suitable species selection, expansion of broadleaf planting, securing adequate growing space, and minimizing excessive pruning.