| Urban forests are an important component of the urban ecological infrastructure and play an important role in improving human welfare and providing ecological services.The health of urban forests relates to the ecological security and sustainable development of the city.Ensuring urban forest health is an important way to establish ecological livable cities.The study of urban forest health has attracted more and more attention under the background of rapid urbanization.This study investigated the urban forests in Shanghai,and established the urban forest health evaluation index system from the sustainable development perspective.Through community survey and environment factors analysis,this research expounded the characteristics of urban forest regeneration and soil quality,and revealed the relationship between plants and environmental factors.Lastly,this study evaluated the health status of urban forest in Shanghai,and explored the potential influence factors.It is expected to provide a theoretical reference for the rational construction of urban forests within a limited urban space,and achieve the healthy and sustainable development of urban forests ultimately.The main conclusions of the study are as follows:1.Evaluation of community structure health of urban forest in ShanghaiThe community structure of urban forest in Shanghai is irrational and the overall health of the community structure is low.A few tree species occupied dominance,such as Cinnamomum camphora,Metasequoia glyptostroboides and Ligustrum lucidum.The species richness,Shannon-wiener index?Simpson index and Pielou index was 2.5?0.39?0.22 and 0.38 respectively.The 172 communities were clustered to 49 types;evergreen broad-leaved forest was the main vegetation type,Frequency of occurrence,with the frequency of occurrence 41.3%.The vertical structure of the community with“tree&shrub&herb”multilayer type accounted to 6.4%,community just exist tree layer accounted to 77.9%.The distribution pattern of tree species was mainly disperse,and urban forests in Shanghai were mostly young and middle age forest.The evaluation results of community structure health showed that:About 33.1%of urban forest community structure health was poor,about 27.3%was very poor,community structure health with excellent,good and middle grade was 1.7%,18.0%and 19.8%respectively.The correlation analysis showed that increasing the species diversity and reducing the impact of human disturbance on the undergrowth plants is an important way to improve the community structure health of urban forest in Shanghai.2.Diagnosing the urban forest regeneration capacity and development trend in ShanghaiThe regeneration capacity of urban forest in Shanghai was low overall;just 25.3%communities could realize self-regeneration.There were 19 families?23 genera,23arbor species?in tree layer,19 families?24 genera,23 arbor species?in shrub layer,and 15 families?19 genera,19 arbor species?in herb layer.Cinnamomum camphora,Metasequoia glyptostroboides and Ligustrum lucidum was high frequency species in tree layer,with frequency of 26.8%,14.8%and 10.6%.Ligustrum lucidum,Cinnamomum camphora,and Broussonetia papyrifera was high frequency species in shrub layer,with frequency of 45.6%,45.6%and 40.5%.Ligustrum lucidum,Cinnamomum camphora,and Morus alba was high frequency species in herb layer,with frequency of 41.8%,35.4%and 24.1%.The results of nonparametric independent test showed that there was no significant difference in shrub layer and herb layer regeneration density among different vegetation types and ages?p<0.05?.Diagnosing the urban forest regeneration capacity in Shanghai,revealed that 62.0%of sample plots have very poor regeneration ability,regeneration capacity with excellent,good,middle and poor was 24.1%,2.5%,6.3%and 5.1%.The paper further analyzed the development trends of urban forest.The results showed that 25.3%of the communities could achieve self-regeneration.27.8%of the communities will be replaced by other community types with retaining the original tree species.Community types without the original tree species will be replace other 32.9%of the communities,and 13.9%of the communities will face degeneration or even die-out without regeneration.Increasing shrub layer and herb layer coverage and species diversity can increase the regeneration capacity of understory species.The effects of limited seed sources and human disturbance on community regeneration ability may be more significant compared with the characteristics of urbanization,3.Comprehensive assessment of Soil quality of urban forest in ShanghaiGenerally,there were no excellent quality soil,the quality of the urban forest soils in Shanghai was poor.Soil density in 0-10 cm layer(1.37 g·cm-3)was significantly lower than that in 10-30 cm(1.46 g·cm-3)and 30-100 cm layers(1.46 g·cm-3).Soil pH increased with the increase of soil depth?7.63,7.84 and 8.01?.The soil electrical conductivity(0.10-0.12 mS·cm-1)was lower than requirement of greening and planting(0.15-0.9 mS·cm-1).Soil total nitrogen,total phosphorous,organic matters and available nitrogen decreased with the increase of soil depth,and their contents in 0-10cm were significantly higher than those in 30-100 cm layer?p<0.05?.Content of Cu,Pb and Zn exceeded the background values of Shanghai?BVs?,and decreased with the increase of soil depth,there were no significant difference among different layers?p<0.05?.The results of nonparametric independent test showed that soil physical and chemical properties and heavy metal contents among different vegetation types and ages have no significant difference?p<0.05?.Assessment results of soil quality showed that:none of the urban forest soil obtained an‘excellent'grade,62.1%of the urban forest soil was poor,34.8%of the urban forest soil was middle,and soil quality with good and very poor grade was both1.5%.The assessment results of geo-accumulation index(Igeo)showed that:when the BVs of Shanghai was taken as the reference,Cu pollution was shown in very few forest soil;when the national soil quality standard?grade II??GBs?was used as the reference,there was no polluted forest soil.The results of potential ecological risk assessment showed that Cu,Pb and Zn in urban forest soil in Shanghai were at low ecological risk level when BVs and GBs values were taken as the reference respectively.Correlation analysis showed that soil organic matter and total nitrogen deficiency were the key factors limiting urban forest soil quality in Shanghai.The increase of urbanization may lead to the increase of soil pH and the decrease of soil nitrogen content.Cu may have a common source of total nitrogen,organic matter,available nitrogen and rapid available phosphorus in soil.We should pay more attention to the potential heavy metal hazards while increasing the content of soil nutrients.4.Comprehensive assessment of urban forest health in ShanghaiThe health status of urban forest in Shanghai was poor.The comprehensive evaluation index system of Shanghai urban forest health was set up using principal component analysis to determine index weights,which covered community structure,community regeneration and soil quality as the criteria layers with 15 indicators.Weight of community structure,community regeneration ability and soil quality was 0.27,0.26and 0.47.The comprehensive evaluation results showed that there was no excellent and health urban forest.The proportion of unhealthy community accounted for 65.2%.Proportion of sub-healthy and bad healthy community accounted for 21.2%and 13.6%.Comprehensive and principal component analysis results of 11 Metasequoia metasequoia communities and 12 Cinnamomum camphora communities showed that more than 50.0%communities were unhealthy respectively.Simple community vertical structure pattern,low regeneration density and lack of total phosphorous were the common limiting factors of the health of Metasequoia glyptostroboides and Cinnamomum camphora communities.At the same time,the high soil pH restricted the health of the Metasequoia glyptostroboides community,and the lack soil electrical conductivity and rapidly available phosphorous restricted the health of the Cinnamomum camphora community.As a whole,in order to improve the healthy and sustainable development of urban forests,their construction and management should apply a“near-nature”method.We should put forward management measures according to community characteristics and the specific demand of soil quality.In addition,we should form the concept of sustainable development and risk prevention awareness from the perspective of ideology,in order to achieve the healthy and sustainable development of urban forests ultimately. |
PDF Full Text Request