Cities have been identified as key actors in climate change mitigation. Nature based carbon sinks have been suggested as a means of mitigating the greenhouse gas emissions of cities. Although there are several studies on the carbon storage and sequestration (CSS) of urban green, the role of residential sites is not fully understood. In addition, the carbon storage of soils is often excluded. Also the implications for planning require more attention. This study estimates the CSS potential of trees and biochar in urban residential yards and identifies effective means to enhance it. Moreover, the study discusses the results at the city scale. The research is based on a case study in Helsinki, Finland, and applies i-Tree planting tool to assess the current and potential life cycle CSS of the case area. The results reveal that trees and the mixing of biochar into growing medium can increase the CSS considerably. The CSS potential of the case area is 520 kg CO₂ per resident during 50 years. The added biochar accounts for 65% of the capacity and the biomass of trees accounts for 35%. At the city scale, it would lead to 330 000 t CO₂ being stored during 50 years. The findings suggest that green planning could contribute more strongly to climate change mitigation by encouraging the use of biochar and the planting of trees, in addition to ensuring favourable growing conditions.

人们已将城市确定为缓解气候变化的主要参与者。已经提出了基于自然的碳汇，以减轻城市的温室气体排放。尽管对城市绿色的碳储存和封存（CSS）进行了多项研究，但住宅用地的作用尚未完全了解。另外，土壤的碳储量经常被排除在外。同样，计划的含义需要更多的关注。这项研究估算了城市居民区树木和生物炭的CSS潜力，并确定了提高其潜力的有效方法。此外，研究讨论了城市规模的结果。该研究基于芬兰赫尔辛基的一个案例研究，并应用i-Tree种植工具来评估该案例区域当前和潜在的生命周期CSS。结果表明，树木和生物炭在生长介质中的混合可以显着提高CSS。案例区域的CSS潜力为520千克二氧化碳50年内每个居民₂个。增加的生物炭占容量的65％，树木的生物量占35％。在城市规模上，这将导致330万吨的CO ₂在50年内被存储。研究结果表明，绿色规划除鼓励确保生物生长条件外，还可通过鼓励使用生物炭和植树来为减缓气候变化做出更大贡献。