Aboveground Carbon Storage and Functional Diversity in Istanbul’s Historical Urban Squares

İstanbul is one of the most densely urbanized and ecologically degraded metropolitan areas in Türkiye, and its limited urban forest resources increase the importance of urban biodiversity and ecosystem services for resilience. This study aimed to evaluate the relationship between aboveground carbon storage, species richness, and functional diversity in tree communities of 10 historical squares in Istanbul. A total of 55 plant species representing 27 families were recorded. Aboveground carbon storage was estimated for each site, and associations with species richness and multiple components of functional diversity were assessed using trait-based analyses. Estimated aboveground carbon storage ranged from 8.6 to 194.3 kg C m−2, with an average of 60.4 kg C m−2. Diameter at breast height, tree height, and crown size were positively associated with aboveground carbon storage. This relationship is especially important in historical squares, where limited opportunities for new planting and spatial redesign make the retention of large, mature trees central to maintaining existing carbon stocks. Site-level patterns further suggest that carbon storage is more closely related to functional structure and biomass-related traits than to species richness alone. Cite this article as: Başaran, N., Yılmaz, H. Ö., & Eroğlu, E. (2026). Aboveground carbon storage and functional diversity in Istanbul’s historical urban squares. Forestist, 76, 0038, doi: 10.5152/ forestist.2026.26038.