Research On Canopy Coverage And Tree Diversity Of Urban Parks Based On UAV Visible Light Image

Based on the UAV visible light image of Bishagang Park,Renmin Park and Zijingshan Park in Zhengzhou,this study combined field surveys to delineate the functional partitions of the three parks,and explored the advantages and disadvantages of three machine learning classification algorithms,namely K-nearest neighbor,Gradient boosting decision tree and Random forest,in classifying visible light image of urban parks and the practicality of UAV visible light image in urban parks;based on the optimal classification algorithm,the tree canopy coverage of each functional zone in the urban parks was obtained and its distribution characteristics were analyzed.At the same time,the tree diversity survey was carried out based on the UAV visible light image,and the Margelef richness index,Shannon-Wiener diversity index,Simple dominance index,Pielou evenness index and tree composition characteristics(family species composition,evergreen-deciduous ratio,proportion of native species,tree density and tree diameter order)were used to comprehensively analyse the tree diversity characteristics of the three parks and each functional zone,and to propose recommendations for the conservation of tree diversity in Zhengzhou city parks.The results showed that:(1)The Kappa coefficients of the K nearest neighbor,Gradient boosting decision tree and Random forest machine learning algorithms are all about 0.8,among which the K-nearest neighbor algorithm is most applicable to the classification of UAV visible light image of urban parks.The tree canopy coverage rates of the three major parks estimated based on the K-nearest neighbor algorithm were,in descending order:Bishagang Park(CC=68.44%),Renmin Park(CC=65.34%),and Zijingshan Park(CC=61.63%).The tree canopy coverage of each functional zone of the park is greater than 30%,which can give good play to the ecological benefits of trees,among which the highest canopy coverage is 85% in the cultural and scientific area of Renmin Park and the lowest canopy coverage is 43% in the children’s play area of Zijingshan Park.(2)A total of 9243 trees were found in the three parks,belonging to 50 families,91 genera and 144 species.Among them,there are 3675 trees in Bishagang Park,belonging to 40 families,71 genera and 99 species,3119 trees in Renmin Park,belonging to 42 families,74 genera and 95 species,and 2449 trees in Zijingshan Park,belonging to 35 families,64 genera and 83 species.There is a high degree of consistency in the major families of the three parks,all of which are dominated by trees of the Rosaceae,Oleaceae,Cupressaceae,and Pinaceae families.(3)There are certain differences in the tree diversity levels in each functional zone of the three parks,the Margalef richness index was distributed between 1.69 and 11.04,the Shannon-Wiener diversity index was between 1.72 and 3.60,and the Simpson dominance index was between 0.76 and 0.96.The three indices had a close positive relationship with the area of the functional partition.There was no significant relationship between the Pielou evenness index and the area of functional zoning.In all three parks,the overall tree diversity level was higher in the ornamental tour area,quiet relaxation area and recreational activity area.(4)The evergreen deciduous ratio in Bishagang Park,Renmin Park and Zijingshan Park was 1:3.7,1:2.5 and 1:2.8,and the proportion of native tree species was 81.8%,76.8% and 75.9%.The evergreen tree species and native tree species preferred by each functional zone have some similarity,and the evergreen tree species are mainly Platycladus orientalis,Cedrus deodara and Ligustrum lucidum,among which the percentage of evergreen tree species in the quiet relaxation area,ornamental tour area and elderly activity area of Bishagang Park is relatively small,about 20%;the native tree species are preferred to Platycladus orientalis,Ligustrum lucidum,Acer buergerianum and Cedrus deodara,etc.,the proportion of native tree species in the children’s play area and cultural science area of Bishagang Park is relatively high,reaching more than 90%,while the utilization of native tree species in the elderly activity area of Zijingshan Park is low at 71.4%.(5)There are great differences in tree density among different functional zones in the three parks.The highest tree density was in the quiet recreation area of Zijingshan Park(278 trees/hm2),and the lowest was in the recreational activity area of Renmin Park(45 trees/hm2).The distribution of tree diameter in each functional zone has some similarity,and most of the functional zones are dominated by medium diameter trees and supplemented by large diameter trees,and the tree diameter at breast height is mainly distributed in the four diameter classes of 10~15cm,15~20cm,20~25cm and >40cm.