Stand Density and Summer Thermal Environment: The Impact of Different Forest Types on Human Thermal Comfort

As urbanization accelerates, the urban heat island effect has significantly impacted the ecological environment and public health.Plant communities, particularly different types of forests, play a crucial role in mitigating the heat island effect through transpiration and shading effects. This study explores the thermal environment regulation characteristics of evergreen forests, deciduous forests, and mixed forests across different seasons, with a particular focus on cooling benefits during the summer. The study also analyzes the influence of vegetation density and sky visibility factors on the thermal environment. The results show that the daytime temperature of evergreen forest (EF1) and mixed forest (MF1) ranged from 36°C to 38°C, whereas the temperature of the lawn (LA) rose to nearly 39°C. At night, the temperature of the lawn dropped sharply to 26°C, exhibiting a large diurnal temperature variation. The black globe temperature (from 14:00 to 16:00) showed smaller fluctuations in the evergreen forest and deciduous forest, with temperatures of 45°C and 47°C, respectively, while the black globe temperature of the lawn and control point reached 52°C and 50°C, respectively, demonstrating more dramatic temperature variations. Physiologically equivalent temperature (PET) values revealed that the lawn (LA) and control point (RP) had PET values of 44°C and 42°C during the day, which fell within the "hot" or "very hot" range, whereas the PET value of the evergreen forest (EF1) remained relatively low, in the "comfortable" range (around 35°C). The study suggests that urban green space design should prioritize the planting of evergreen and mixed forests, optimize canopy density, enhance ecological diversity, and avoid excessive exposure from lawns and open areas. Additionally, integrating techniques such as rooftop greening, vertical greening, and water body design can further improve the thermal comfort of urban green spaces and promote the development of livable green cities.