ZONG Hua, YANG Zhenru, LI He, CHEN Mingkun, YAO Yining, ZHANG Qingyan, LI Qiuyue
Street trees are both the backbone of the street greening system and an important component of the streetscape,with important ecosystem service values. However,there is growing evidence that the pollen released by street trees poses an allergenic risk to public health. The work aims to explore the impact of the species composition and α-diversity characteristics of street trees in the central urban area of the Park City on their pollen allergy risk. Based on field surveys of street trees in two central urban districts of Chengdu,the Pollen Allergy Index (Iugza) is employed to assess the pollen allergy risk and quantify its association with species richness and α-diversity. There are 52 606 street trees in 467 streets in Jinjiang District,belonging to 25 families,32 genera and 35 species. There are 67 121 street trees in 548 streets in Chenghua District,belonging to 26 families,49 genera and 53 species. Ginkgo biloba,Cinnamomum camphora,Ficus concinna,and Cinnamomum japonicum are the dominant tree species of the both districts. In the streets of Jinjiang and Chenghua Districts,young adult trees (Diameter at Breast Height=15.2~30.3 cm) account for the highest proportion at 71.59% and 65.02%,respectively,followed by juvenile trees (Diameter at Breast Height ≤15.1 cm) at 13.32% and 20.97%. After the streets are divided into 5 levels according to width,it is found that the average crown width of street trees in both level 5 and level 4 streets (community roads) is much higher than the cultivation spacing,and there is a serious phenomenon of stacked crowns. The Shannon Wiener Index (Sd) values of streets at all street levels in Jinjiang District and Chenghua District range from 0.64 to 2.58 and 0 to 2.75,respectively,while the Pielou index (Pe) ranges from 0.66 to 0.93 and 0.29 to 0.72,respectively. The proportion of streets with allergy risk between 0.3 and 0.6 is the lowest,7.92% and 7.48%,respectively,while the proportion of streets with Iugza values higher than 0.6 is the highest,76.87% and 81.73%,respectively. In addition,the proportion of streets with high Iugza values (>0.6) is more than 83% in both districts in street level 5,showing a very high risk of pollen allergy. Pearson correlation analysis reveals that the Iugza values of Chengdu's streets exhibit a positive linear correlation with Sd values and a highly significant positive correlation with tree species richness. To reduce allergen production,a series of green management strategies are finally targeted to enhance the health and well-being of Park City residents.
