Constraints to urban trees and their remedies in the built environment

Low-density urban areas have ample above- and below-ground room for trees. This study is focused on high-density or compact urban areas where the competition for space is intense, and where the grey infrastructure prevails to suppress the urban green infrastructure (UGI) (Urban et al., 1988; McPherson et al., 2001). Under these challenging circumstances, trees can grow physically restricted and physiologically stressed (Jim, 1998; Jim and Chen, 2008; Jim and Zhang, 2013).