Optimization Of Plant Community In Urban Parks Of Huaihua City Based On Ecological Benefits Analysis

A strategic goal of Huaihua city set in 2021 was to build it into a national ecological garden city in order to improve its ecological environment.Urban parks are playing a critical and integral part of urban green space,whose construction is one of the major tasks in creating an ecological garden city.Plant community structure can greatly influence the ecological functions of urban park green space,such as cooling and humidification,carbon fixation and oxygen release,and absorption of harmful gases.In today’s plant allocation in many urban parks in China,much importance is attached to the landscape and less to the ecology benefits.Few researches have focused on plant community structure and plant diversity in urban parks of Huaihua city.Therefore,by comparing Huaihua urban parks with scenic recreational green space there in their plant community structural features and ecological benefits,the paper figures out the main deficiencies in plant allocation and puts forward plant community optimization measures in urban parks of Huaihua,which is of great theoretical and practical significance for Huaihua and other cities in the surrounding area to allocate plants scientifically in the process of building the national ecological garden city.In this research,based on literature review and data collection,the present situation of 130 plant communities in scenic recreational green spaces and urban parks in Huaihua city were investigated by using the typical sample plot method.The general characteristics and the rationality of plant number composition of 127 plant communities were analyzed,and the species composition,quantitative characteristics,vertical structure,and plant diversity of 73 broad-leaved forests and mixed broadleaf-conifer forests were compared and analyzed.Based on the measured cooling and humidifying value of 48 plant communities during the high temperature period of 11:00-15:00 in summer,and the effect of three-dimensional green biomass on the cooling and humidification function was analyzed.Also,45 of these plant communities were selected as research objects,and a comprehensive landscape evaluation index system of park plant community was established based on their ecological function and visual effect.The author applied principal component analysis method to determine the weights of evaluation indexes,and comprehensive landscape evaluation index formula to calculate the comprehensive score and determine evaluation grade of each plant community.The ecological benefits of afforestation per unit area of plant community were measured,including dust retention,SO2 absorption,CO2 fixation,O2 release,and summer transpiration quality and value based on three-dimensional green biomass.A comprehensive ecological benefits evaluation index formula was applied to calculate the evaluation score of ecological benefit quality and determine the evaluation grade of each plant community.The deficiency of plant configuration in urban park green spaces was summarized,the main advantages of plant community in scenic recreational green spaces were extracted,a number of excellent plant communities were recommended,and suggestions for plant community optimization were put forward.The main results are as follows.(1)The comprehensive landscape evaluation grade of plant community is high and the ecological benefit is strong in scenic recreational green spaces of Huaihua city,while the comprehensive landscape evaluation grade of plant community is low and the ecological benefit is weak in urban parks.The parks built for a long time have higher comprehensive landscape evaluation grade and stronger ecological benefits than new parks.Sixteen plant communities are evaluated as grade I,including 12 in scenic recreational green spaces and 4 in urban parks.Nine plant communities are evaluated as strong in ecological benefits,including 7 in scenic recreational green spaces and 2 in urban parks.(2)Huaihua urban parks have a total of 462 plant species affiliated to 108 families and 278 genera,including 327 species of woody plants,135 species of herbaceous plants.Among the 73 broad-leaved and coniferous mixed communities,as for urban park plant communities,the average Shannon-wiener diversity indexes of tree,shrub and woody ground cover are 1.3700,0.7468,and 0.6426 respectively.As for plant communities in scenic recreational green spaces,the average Shannon-wiener diversity indexes of tree,shrub and woody ground cover are 1.8813,1.2846,and 1.3912 respectively.(3)Among the plant communities used for ecological benefits evaluation and comprehensive landscape evaluation in scenic recreational green spaces of Huaihua city,the average number of plant species is 26.The average Shannon-wiener diversity indexes of tree,shrub and woody ground cover are 1.9052,1.2866,and 1.3954 respectively.The average Simpson dominance indexes of tree,shrub and woody ground cover are 0.7716,0.6077,and 0.6212 respectively.The total three-dimensional green biomass density is 7.71 m3/m2 on average,with deciduous trees accounting for 46.00%.The average number of layers is 4.2.Among the plant communities used for ecological benefits evaluation and comprehensive landscape evaluation in urban parks of Huaihua city,the average number of plant species is 16.The average Shannon-wiener diversity indexes of tree,shrub and woody ground cover are 1.4979,0.8339,and 0.7176 respectively.The average Simpson dominance indexes of tree,shrub and woody ground cover are 0.6880,0.4285,and 0.3852 respectively.The total three-dimensional green biomass density is 3.93 m3/m2 on average,with deciduous trees accounting for 38.00%.The average number of layers is 2.91.(4)The height of plant community,the number of layers,the total three-dimensional green biomass density,and the three-dimensional green biomass density of trees and shrubs are significantly positively correlated with the cooling and humidification rate,while the three-dimensional green biomass density of ground cover plants is significantly negatively correlated with the cooling and humidification rate in the multi-layered plant communities of urban parks and scenic recreational green spaces in Huaihua city.When the community height is 18.0 m,the cooling rate reaches 20.44%.When the plant community height is 22.3 m,the humidification rate reaches 65.10%.When the total three-dimensional green density of plant community is close to 11.2 m3/m2,the cooling rate of green space reaches 23.34%.When the total three-dimensional green density is close to 12.1 m3/m2,the green space humidification rate reaches 66.83%.When the three-dimensional green density of trees is close to 9.9 m3/m2,the cooling rate of green space reaches 22.23%.When the three-dimensional green density of trees is close to 11.08 m3/m2,the humidification rate of green space reaches 65.54%.When the three-dimensional green density of shrubs is close to 0.53 m3/m2,the cooling rate of green space reaches 23.40%.When the three-dimensional green density of shrubs is close to 0.63 m3/m2,the humidification rate of green space reaches 71.49%.(5)Compared with scenic recreational green spaces,Huaihua urban parks have smaller community height and stratification number,simpler hierarchical structure,small total three-dimensional green biomass density,poor cooling and humidification ability in summer,and weak ecological benefit.With fewer plant species,lower diversity and obvious dominance,plants of certain families,genera and species accounted for an excessive proportion and the composition of plant number is unreasonable.Fewer saplings are regenerated and the degree of naturalization is low.There are small plant density,small height difference and unreasonable vertical distribution with trees and shrubs,but large density with ligneous ground covers.The cost of maintenance and management is high.Based on the deficiencies above,optimization strategies are put forward,such as controlling the excessive planting of some plants,optimizing the composition of plant quantity,enhancing the development and utilization of native plants,reasonably introducing exotic plants to enrich plant diversity,making full use of the existing plants,realizing a scientific allocation of plants,and strengthening green space conservation and management.Seven excellent plant communities are recommended,and specific optimization suggestions are put forward in view of the main problems existing in urban parks.