Study On The Shading Effect Of Common Sidewalk Trees On Pavements In Guangzhou

In this study,7 common sidewalk trees in Guangzhou were selected as the research objects,and 6 comprehensive shading effect indexes and 9 tree structure indexes were measured,calculated,and analyzed.Established the relationship between comprehensive shading effect index and tree structure index through correlation analysis and stepwise multiple linear regression analysis.The strategy to improve the shading effect are proposed.The main findings are as follows:(1)The influence of 7 street trees on 6 comprehensive shading effect indicators.The maximum cooling rate Mangifera indica reaches 7.81% at 14:00,the maximum shading rate Ficus microcarpa reaches 90.44% at 13:00,and the maximum humidification rate Michelia × alba reaches 20.84% at 17:00.The whole-day average cooling rate from high to low is: F.microcarpa,Mangifera indica,Michelia × alba,Bischofia javanica,Dracontomelon duperreanum,Terminalia neotaliala,Delonix regia;the whole-day average shading rate from high to low is: F.microcarpa,D.duperreanum,B.javanica,Michelia ×alba,Mangifera indica,D.regia,T.neotaliala;The whole-day average humidification rate from high to low is: Mangifera indica,Michelia × alba,F.microcarpa,D.duperreanum,B.javanica,T.neotaliala,D.regia;the whole-day average shading area from high to low is:Mangifera indica,D.duperreanum,Michelia × alba,F.microcarpa,B.javanica,D.regia,T.neotaliala;The average shading quality of the whole day is from high to low: F.microcarpa,Michelia × alba,Mangifera indica,D.duperreanum,B.javanica,T.neotaliala,D.regia;The average comprehensive shading effect of the whole day is from high to low:Mangifera indica,F.microcarpa,D.duperreanum,Michelia × alba,B.javanica,D.regia,T.neotaliala.At 14:00,the cooling rate from high to low is: Mangifera indica,Michelia ×alba,F.microcarpa,D.duperreanum,B.javanica,D.regia,T.neotaliala.At 14:00,the shading rate from high to low is: D.duperreanum,F.microcarpa,B.javanica,Michelia ×alba,Mangifera indica,T.neotaliala,D.regia.14:00 Humidification rate from high to low:Mangifera indica,Michelia × alba,F.microcarpa,B.javanica,D.duperreanum,T.neotaliala,D.regia.14:00 The shade quality from good to bad is: Michelia × alba,Mangifera indica,F.microcarpa,D.duperreanum,B.javanica,D.regia,T.neotaliala.At14:00,the comprehensive shading effect from good to bad is: Mangifera indica,Michelia ×alba,D.duperreanum,F.microcarpa,B.javanica,D.regia,T.neotaliala.(2)Factors affecting the comprehensive shading effect index of 7 kinds of street trees.1)The cooling effect of street trees is the greatest between 12:00-15:00 noon;F.microcarpa the cooling rate fluctuates the least,the value is the largest,the change trend is stable throughout the day,and the average daily cooling rate F.microcarpa is the best.2)The change of shading rate maintains a steady trend at 10:00-15:00,and rapidly weakens at15:00-17:00.The shading rate of D.regia fluctuates the most,followed by T.neotaliala.3)It is verified that the method of simulating sunlight by Sketch-Up to obtain the change of shade area is feasible.Although the tree height,crown height,crown width and leaf growth height of Mangifera indica are not ranked well,the shade area is the largest.From 15:00 to17:00,the shading area of D.duperreanum and F.microcarpa increased the most,followed by Mangifera indica,Michelia × alba,and B.javanica,and the smallest increase was T.neotaliala and D.regia.4)The smallest fluctuation of shade quality in F.microcarpa is due to the optimal and stable cooling rate and shading rate of F.microcarpa.The shade quality of Mangifera indica and Michelia × alba reached the maximum at 14:00.(3)There is a very significant positive correlation between the comprehensive shading effect and the index.The cooling rate,shading rate,humidification rate,shading quality,shading area and comprehensive shading effect were all significantly positively correlated;The change of cooling rate had the greatest influence on the comprehensive shading effect,followed by shading area and shading rate.The higher the humidification rate of street trees,the better the cooling rate,shading rate,shade quality,shade area,and comprehensive shading effect.(4)There is a close relationship between the tree structure index and the comprehensive shading effect index.Tree height,diameter at breast height,crown width,crown height,leaf height,leaf thickness,leaf area,leaf area index are highly correlated with cooling rate,among which crown height,leaf growth height,diameter at breast height have the greatest influence on cooling rate.,leaf thickness;tree height,diameter at breast height,crown width,crown height,leaf growth height,leaf thickness,leaf area index and shading rate are highly correlated,among which leaf area index and crown height have the greatest influence on shading rate in order;Tree height,diameter at breast height,crown height,leaf growth height,leaf area are highly correlated with humidification rate,among which diameter at breast height and leaf area have the greatest influence on humidification rate;tree height,diameter at breast height,crown width,crown height,Leaf height,leaf thickness,leaf area,leaf area index were highly correlated with shade area;tree height,DBH,crown width,crown height,leaf height,leaf thickness,leaf area,leaf area index were correlated with shade quality tree height,diameter at breast height,crown height and comprehensive shading effect were highly correlated,among which crown height,leaf growth height,diameter at breast height,leaf area index and leaf area had the greatest influence on comprehensive shading effect.(5)Improve the shading effect of street trees through tree species selection and pruning.According to the influence of different tree species on the comprehensive shading effect,combined with the tree structure factors,it is recommended to select the tree species with good cooling rate and shading rate,high crown height,and low leaf growth height as street trees.Adequate growth space and avoid building shading and excessive canopy reduction to maintain a symmetrical leaf distribution and tree canopy shape.In addition,replant the existing less-shading tree species to improve the shading effect of street trees.