Linking Greenery Visibility Analysis and Urban Tree Planting Decisions by Quantifying the Visible Greenery Provision of Individual Street Trees

Source abstract

Visible greenery, an important contribution of urban street trees, has been shown to correlate with the spatial quality of streets, as well as with people's health and well-being. However, existing approaches provide limited support for quantifying the site-specific visible greenery contribution of individual trees, thereby constraining the evaluation of specific trees and the comparison of alternative planting locations and spatial configurations. To address this research gap, this study proposes Tree-based Visible Greenery Provision (tVGP), a metric that quantifies the visible greenery contribution of individual trees across selected viewpoints, and develops a 3D visibility analysis-based tool for its calculation. The tool comprises four main steps: data preparation, simulation of the 3D visibility of trees, classification of sightlines by tree ID, and calculation of tVGP. It was applied to a study area near the center of Munich, Germany, to test the feasibility of calculating tVGP for existing street trees and compare hypothetical planting configurations. A preliminary comparison with panoramic photographs showed that the simulated results captured relative differences in visible greenery at the individual-tree level. The applications further demonstrated that the tool can identify site-specific variation among existing trees, distinguish the contributions of individual trees to viewpoint-level visible greenery, and compare planting alternatives under different tree numbers and spatial configurations. Within the evaluated scenario space, the analysis of planting configurations showed nonlinear increases and diminishing gains in the highest tVGP as tree number increased, together with substantial variation among configurations containing the same number of trees. The proposed tool provides a site-specific framework for linking visible greenery analysis with individual-tree assessment and the relative comparison of alternative street-tree planting options under consistent spatial and simulation settings.