Localized assessment of urban forest structures with 3D indicators

Urban trees, as nature-based solutions, are crucial for climate change adaptation, biodiversity, and human well-being. Although heterogeneous vertical structures are inherent to urban spaces, decisions on tree preservation and planting often rely on 2D assessments, not accounting for the vertical dimension. This study evaluates the added value of 3D data in informing such decisions. A comprehensive analysis of localized differences between 2D and 3D urban forest structure and morphology was conducted for the cities of Amsterdam (Netherlands) and Berlin (Germany) on a 100 × 100 m grid, using spatially explicit indicators. The relationship between horizontal and vertical forest structure was assessed by analyzing mean canopy height relative to canopy coverage. While canopy height generally increased with canopy coverage, high vertical heterogeneity was observed across all urban forest structures. A quadratic regression of canopy coverage against the canopy 3D index revealed a complex, non-linear relationship, indicating vertical structure cannot be reliably predicted from horizontal data alone. Furthermore, evaluating the impact of vertical structures on the spatial relationship between trees and buildings revealed patterns linked to urban morphology. Although significant variation was observed, 2D assessments tended to indicate tree proportions up to 25 % higher than volume-based measurements in building-dominated areas, while indicating lower proportions in tree-dominated areas. Overall, the study revealed large local and site-specific differences in vertical structures that could not be inferred from 2D data. By explicitly accounting for data resolution, spatial scale and context, the added value of 3D assessments for managing the ecosystem services provided by urban trees was demonstrated. • Localized 2D-3D analysis of urban tree structure and morphology across two cities. • Vertical complexity captured by 3D indicators exceeds 2D prediction capabilities. • In urban centers 2D tree-to-building ratios indicate higher values than 3D. • Higher tree-to-building ratio in urban centers indicated by 2D methods. • 3D assessments provide a more comprehensive understanding of urban forest structure.