A Study On The Microclimate Regulation Functions Of Urban Forests In Harbin And Changchun City And Possible Association With Various Factors

Field observation on urban forests shading,cooling humidification effect and its influencing factors,is a foundation to build an urban greening engineering with better environmental effect,while a systematic large-scale study is limited.The study analyzed the 4forest types of urban forests in Harbin and Changchun city respectively(Affiliated Forests,Roadside Forests,Landscape Forests and Ecological Welfare Forests).Tree growth-related parameters and environmental factors(inside and outside the forest)were measured simultaneously.The quantitative studied of differences between 4 forests types in shading,cooling and humidifying effects and their associations with the environmental and tree growth characteristics.The aims of this study were to provide scientific basis for the evaluation and management of urban forest ecological service functions.This paper compared the differences between urban forests ecological service functions,tree size and external climatic conditions between Harbin and Changchun city,which provides the theoretical basis for the management of urban trees and the optimization of urban forests structure.This study reached the following results:(1)Urban forests produced a 77%~90%reduction of sun lights(shading effect)and 4.5%increases in relative humidity(humidifying effect).The horizontal average cooling effect was2.95 ? lower than open sites(outside forests).Soil cooling effect was about 1~2 ? lower under canopy than outside forests.But the vertical cooling was poor.Shading,cooling and humidifying effects were significant differences among 4 different forest types.The comprehensive scores for all these microclimate regulations demonstrated that LF was 19%higher than the other 3 forest types on average.Xiangfang District urban forests shading,cooling(horizontal,vertical,soil)effect was better than other administrative regions,and the best humidifying effect in Songbei District.Urban forests had much stronger regulating functions at high air temperature,low air humidity sunny days.Moreover,4 tree-growth factors[tree height,canopy area,under branch height and DBH(diameter at breast height)]had significant influences on temperature reduction and relative humidity increase,and the general patterns were that larger trees usually accompany with higher regulating functions,but its influence was less than environmental factors.Our findings highlight that different forest types in different urban regions had dramatically different ecological service functions,and comparison among forest types facilitates urban tree management for maximizing microclimate regulations functions.For the landscape forests,we should continue to maintain its high ecological service functions and strengthen the management of the forest types with low environmental regulation ability.(2)Urban forests could reduce 74%~86%of incident sun lights,3%~7%increase in air relative humidity in Changchun city.The horizontal average cooling effect was 3.5 ?;Soil cooling effect was about 1? lower under canopy than outside forests.The vertical cooling effect characterized as canopy temperature about 1? lower than under canopy temperature.Shading,cooling and humidifying effects significantly differed among the 4 forest types located at different urban regions,and comprehensive scores for all these microclimate regulations showed a peak value in AF.The overall score is expressed as AF>RF>EF>LF.The spatial distribution map showed that microclimate regulation functions of the city center was poor,the best in Chaoyang Distric.Regress analyses and redundancy analysis revealed that urban forests had much stronger regulating functions at high air temperature,low air humidity sunny days,while a general pattern of larger trees usually accompany with higher regulating function in cooling,shading and humidifying effects.(3)Urban forest trees were small and mostly in Harbin and Changchun city(<10m),which may lead to their low ecological service functions and could not give full play to their ecological benefits.Compared with the two cities,the trees size of Harbin was significantly higher than that of the Changchun 21cm,and the canopy size was significantly larger than that of Changchun 25m~2,and the DBH was significantly higher than that of about 25cm.The external climate of Changchun was hotter than Harbin.Changchun city light radiation was1.45-fold higher than Harbin,the temperature was 1.1? higher than Harbin.The shading of Harbin urban forests was significantly higher than that of Changchun,but it was lower than that of Changchun in terms of cooling(horizontal and vertical)and humidifying effects.