Exploring the ecosystem services delivered by urban woody plants at Çankırı Castle

Urban green spaces are becoming more widely acknowledged for their capacity to offer a variety of ecosystem services, such as supporting, regulating, and cultural roles, all of which enhance the general sustainability of urban settings. Trees and vegetation have been added to many planned cities to improve air quality and slow down climate change, but little is known about the traits and patterns of urban nature and ecosystem services in smaller cities. Smaller cities like Çankırı, particularly the historically and environmentally significant Çankırı Castle, remain understudied despite their unique ecological and climatic conditions; its selection as a case study highlights the crucial role of urban vegetation in mitigating climate challenges and enhancing sustainability in semi-arid environments. The purpose of this study was to assess the woody plant species in Çankırı Castle, to identify 10 tree species with the highest importance values, to estimate the removal of pollutants (CO, O₃, NO₂, SO₂, PM₁₀, and PM_2.5), to evaluate carbon storage, carbon sequestration, oxygen production, and avoided runoff using the i-Tree Eco model, and to reveal the relationships of diameter at breast height with these ecosystem services. The study showed that O₃ ranked first for pollution removal (31.2738 kg/yr) and second for economic value ($18.0735/yr), while PM₁₀ had the highest economic value for removal ($318.0080/yr) but ranked second in quantity (11.1354 kg/yr). The total carbon storage, sequestration, oxygen production, and avoided runoff of the 10 highest-ranking species were 71,300 kg/yr, 3,040 kg/yr, 8,048 kg/yr, and 32,370 mm/yr, respectively. This study highlights the key role of urban green spaces in providing essential ecosystem services, with species like Pinus sylvestris, Fraxinus excelsior, and Cedrus libani significantly contributing to carbon storage, sequestration, oxygen production, and runoff mitigation. However, species such as Pinus nigra and Prunus mahaleb, despite being abundant, have limited ecological contributions, emphasizing the importance of strategic species selection. The study also reveals that while diameter at breast height is crucial for carbon sequestration, factors like tree density and leaf area play significant roles in mitigating runoff, underscoring the need for a comprehensive approach to urban forestry.