Cooling and humidifying effect of plant communities in subtropical urban parks

Urban vegetation has been proved to play an important role in mitigating the heat island effect. However, it is not clear how independent small-scale plant communities affected the microclimate. In this paper, the effects of fifteen plant communities on temperature and relative humidity were investigated from November 2010 to October 2011 in urban parks in subtropical Shenzhen City, China. The canopy density, canopy area, tree height and the background climate conditions under plant communities were measured. The effects of small-scale plant communities on temperature and relative humidity were the most significant at 1400–1500 h during the day. The temperature reduction and relative humidity increase due to small-scale plant communities were higher in summer, followed by autumn, spring and winter. As compared to the control open sites, the temperature reduction due to plant communities ranged from 2.14 °C to 5.15 °C, and the relative humidity increase ranged from 6.21% to 8.30%. We found that multilayer plant communities were the most effective in terms of their cooling and humidifying effect, while bamboo groves were the least effective. Regression results revealed that four factors, namely canopy density, canopy area, tree height and solar radiation, had significant influence on temperature reduction and relative humidity increase.