Abstract: [Objective] It is of significance to investigate the temporal variations of microclimate and the extent of human comfort in forests for developing rational management strategies, assessing the ecological benefit of urban recreational forests, and providing guidance for local residents to choose befitting time and clothing for recreation in the forests.[Method] Three typical plantation forests for recreational purposes nearby the highest peak of Huishan National Forest Park in Wuxi City were selected to compare the differences of microclimate and the extent of comfort between forests and open area with no forest. The three forests planted in the 1980s and 1990s were respectively of Cinnamomum camphora, Pinus elliotii on the southern slope, and Quercus variabilis on the northern slope. A site on a cement road on the mountain ridge was taken as the control. The air temperature, air relative humidity and wind velocity were measured in the field during the day time (5:00 am-19:00 pm) on calm sunny days in the spring, summer, autumn and winter, respectively. Comfort index and weather index for clothing thickness were calculated to quantify the seasonal and diurnal variations of microclimate and extent of human comfort.[Result] The results showed that seasonal variations of temperature in all forests exhibited a greater extent in summer than in spring, autumn, and winter while the air relative humidity in summer and autumn were greater than that in spring and winter. The highest wind speed in the C. camphora stand and P. elliotii stand occurred in summer but Q. variabilis stand and the control site were in autumn. There was no significant difference in the extent of human comfort among different forests in the same season and the most comfortable season for all forests were in spring. Single-peak diurnal variation of air temperature was found in all forests with temperature peak from 11:00am to 15:00pm and troughs from 5:00am to 7:00am in all the four seasons. However, the daily variation of air relative humidity exhibited an opposite trend. Large fluctuations in wind speed demonstrated by peaks and troughs respectively occurring during 5:00am-9:00am and 13:00pm-15:00pm, The daily extent of human comfort peaked in spring, autumn and winter during 11:00am-15:00pm while dropped to the lowest values in summer. The extent of human comfort of the three forests was improved significantly in summer but not in winter. The longest period of climate reached the comfort level in each forest was in spring (11:00-17:00), followed by autumn (11:00-15:00) and summer (5:00-7:00), yet the weather was extremely uncomfortable in winter. The weather index for clothing thickness (WICT) of all forest stands was 1 in summer and 7 in winter. In spring, the WICTs were different among the forest stands, with 5 for C. camphora stand, 4 for both P. elliotii and Q. variabilis stand, and 3 for the control site. In autumn, the WICT was 4 for the control site and Q.variabilis stand, and 5 for C. camphora and P.elliotii stand.[Conclusion] The three mature plantation stands all played a cooling and humidifying effect in spring, while the P. elliotii stand showed an effect of wind speed reduction in all seasons. The seasonal and diurnal variation trends of microclimate factors and the extent of human comfort among three recreational forests indicated that microclimate was biophysically regulated in summer, and the climate in spring was the most comfortable for human.

Key words: microclimatic effect, extent of human comfort, urban recreational forest, temporal variation