Preferences for street configuration and street tree planting in urban Hong Kong

This study aimed to explore people's perception of tree planting in street canyons and the perceived tree impacts through a questionnaire survey. Also, by using a discrete choice experiment, it aimed to reveal how people performed tradeoffs among three streetscape attributes: namely permeability (i.e. spacing between buildings), aspect ratio (i.e. ratio of street width to building height), and tree planting. A secondary aim was to determine respondent's willingness to pay for streetscape features and tree planting. Despite published research results that indicate tree planting can have a negative impact on air quality, the survey results from 509 respondents in Hong Kong indicated that the majority of them held positive views of tree planting in street canyons. The probability of having an overall positive view was found to be higher if an individual perceived that trees could improve air quality, provide shading or did not obstruct footpaths. The preferred streetscape was high permeability, regardless of whether respondents thought that trees could or could not contribute to improving air quality. However respondents who perceived that trees could improve air quality preferred tree planting at both sides of the street over lower aspect ratio whereas those who perceived that trees did not improve air quality preferred low aspect ratio over tree planting at both sides of the street. Both sets of respondents did however agree on the preferred order of tree planting options, namely planting on both sides of the street was preferred to planting at the center of the street which in turn was preferable to no tree planting at all. The overall willingness to pay was estimated to be HK$163.4, HK$132.4 and HK$121.1 per month for high permeability, street-level tree planting and low aspect ratio, respectively. The study clearly identifies high permeability as the most preferred planning option. However, the perception held by the majority of respondents that trees can improve air quality is contrary to recent research findings. This poses a dilemma for urban planners in that schemes that may be more beneficial, i.e. low aspect ratio, may face more public opposition than less beneficial schemes involving tree planting. Although the study was conducted in Hong Kong the findings should be applicable to other modern metropolises characterized by high rise buildings.