Influence of Street Tree Density on Transpiration in a Subtropical Climate

Abstract

In order to alleviate the urban HI (Heat Island) effect, green belt planning has recently been considered one of the priorities in the urban environment greening. This study discusses the influence on microclimate which may be brought by boulevards consisting of different tree species and their allocations. Combining the results of Sap Flow Measurement with the analyses on dense and open canopy, four findings were concluded: (1)Street trees have a critical influence on easing urban HI effect. (2)The amount of tree transpiration in open canopy is larger than that of in dense canopy due to heated ground. (3)The variations of humidity in both dense and open canopy have little difference. (4)In order to lower the surrounding temperature, boulevards of dense canopy in cities appear to be more effective than that of open canopy. The results point out that allocation of street trees plays a critical role in cooling down the surrounding environment. Hence, improving urban roads’ environment through planning planting allocations is feasible and effective. In this study we have proposed several allocation designs of street trees that could serve as a reference for planning the planting of urban street trees.