Effects of Tall Buildings on Visually Morphological Traits of Urban Trees

The visual morphology of trees significantly impacts urban green micro-landscape aesthetics. Proximity to tall buildings affects tree form due to competition for space and light. The study investigates the impact of tall buildings on six visually morphological traits of eight common ornamental species in urban micro-landscapes in Beijing, with the distance and direction between trees and buildings as variables. It found that as trees grow closer to buildings, most angiosperms show increased crown asymmetry degree and crown loss, and reduced crown round degree and crown stretch degree (i.e., Sophora japonica L. and Acer truncatum Bunge saw a 52.26% and 47.62% increase in crown asymmetry degree, and a 20.35% and 21.59% decrease in crown round degree, respectively). However, the pattern of crown morphological changes in gymnosperms is poor (the closer the distance, the lower the height-to-diameter ratio of Pinus tabuliformis Carr., while the height-to-diameter ratio of Juniperus chinensis Roxb. significantly increases). In terms of orientation, gymnosperms on the west side of buildings have a greater crown asymmetry degree. It suggests that planting positions relative to buildings affect tree morphology. Recommendations include planting J. chinensis closer to buildings but keeping angiosperms like Fraxinus velutina Torr., S. japonica, and A. truncatum more than 3 m away to ensure healthy crown development.