Abstract
Mitigating extreme heat in urban areas is beneficial and sometimes critical to human health. Thriving plant communities in community parks play an important role in mitigating extreme heat through providing cooling effect, while inevitably affecting how people perceive the benefits of using community parks for recreation. Thus, the impacts of plant communities on the thermal environment should be quantified to determine the optimal structure of the plant community. The goal would be to harmonize the functions of improving the thermal environment with the preferences people have related to the recreational benefits of plant communities with various levels of vegetation density. In this paper, the correlations between the structural characteristics of plant communities and their function in mitigating the thermal environment were investigated on calm summer days in Xincheng Central Park, Minhang District, Shanghai, China. In addition to analyzing the plant communities present and their effects on the park microclimate, a questionnaire was employed to determine the plant community preferences of recreational park users. The results showed that plant communities could reduce the air temperature by 1.23–2.42 °C and increase the relative humidity by 2.4–4.2% during the daytime. The microclimate conditions in plant communities with varying vegetation densities were significantly different. The canopy density and leaf area index primarily controlled the temperature reduction, while the canopy density and total canopy cover ratio primarily controlled the increase in humidity; meanwhile, these correlations varied at different times of the day. Moreover, most of the park users preferred a moderately dense plant community which met their environmental perceptions for recreation in parks. Age or education level variables of park users would also predict preferences for different plant community densities. Ultimately, one plant community pattern with appropriate canopy density (60%), leaf area index (≥3) and canopy cover ratio (total 0.80–1.20, with 0.6–0.75 for trees and 0.20–0.45 for shrubs/woodland area) was recommended, which would harmonize the functions of the mitigation of the thermal environment with most people’s perception of a desirable vegetation density.
Highlights
As urban populations grow and expand, the creation of urban heat islands (UHIs) have been aggravated mainly by the creation of impervious ground surfaces, the loss of vegetation, and generation of anthropogenic heat that is released from industrial and of human activities [1,2,3,4]
Many studies have been conducted, confirming that in addition to increasing air and surface temperatures in urban areas, UHIs can result in increased water and energy consumption for air conditioning as well as an increase in the concentration of ground level pollutants; these changes influence the habitability of cities and can even lead to direct or indirect harm to human health [5,6,7,8]
We aimed to 1) find whether there was a significant difference in the microclimate conditions of plant communities varying in vegetation density; 2) quantify the ability of vegetation structure features on diurnal variation in cooling and humidifying effects; 3) survey the plant community scenes that most respondents preferred for outdoor recreation in urban parks; 4) recommend a plant community structure with high cooling ecosystem service on hot summer days that could meet most respondents’ environmental perceptions of a desirable vegetation density for outdoor recreation
Summary
As urban populations grow and expand, the creation of urban heat islands (UHIs) have been aggravated mainly by the creation of impervious ground surfaces, the loss of vegetation, and generation of anthropogenic heat that is released from industrial and of human activities [1,2,3,4]. Numerous studies have been conducted to measure and evaluate the ability of vegetation to regulate the microclimate of urban areas [12, 16, 17], to adapt to patterns of climate change [13], to reduce energy use [18], and to improve the comfort of the urban population [19, 20]. Zhang et al (2013) investigated the interrelations between the structural characteristics of plant community and microclimate conditions, which testified canopy density, canopy area, tree height and solar radiation as the main factors influencing the cooling and humidifying effects from plant communities significantly [22]
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