Study On Structural Characteristics And Health Assessment Of Urban Riparian Forests In Beijing

The urban riparian forest is an artificial plant community.As an important part of urban forest,it has distinct environmental effects.This paper researched on urban rivers within the Sixth Ring Road of Beijing and carried out field investigations of the growth structure and health factors of riparian forests along 29 rivers.And the paper preliminarily discussed the structural characteristics and diversity changing rules of the urban riparian forest species and their undergrowth shrubs in different grades of rivers,different hardening river banks and different road gradients.On this basis,individual and group scales were used to build a forest health assessment model to evaluate the health status of forests,with an aim to provide a reference for the construction and healthy management of urban riparian closing to nature plant community.The main results were as follows:1、There are 119 species,75 genera,40 families of urban riparian forest in Beijing,including 82 species,49 genera,31 families of arbors,37 species,28 genera,14families of shrubs.Ratio of arbor to shrub was 1.9∶1.2、The top 12 tree species with higher frequency of urban riparian forests in Beijing were Salix babylonica,Sophora japonica,Ulmus pumila,Pinus tabuliformis,Populus X canadensis,Fraxinus chinensis,Sabina chinensis,Ginkgo biloba,Broussonetia papyrifera,Robinia pseudoacacia,Ailanthus altissima and Morus alba,among which Salix babylonica has the highest frequency,up to 64.2%.3、The relative abundance,relative significance and important values of Salix babylonica were the largest,and they were the main establishment species and dominant species.And the tree hierarchy dominant specieswere Populus X canadensis and Sophora japonica.The sum of the important values of the top 12 trees in within 2^nd ring road,2^nd-3^rd ring road,3^rd-4^th ring road,4^th-5^th ring road and 5^th-6^th ring road was 81.0%,77.7%,81.5%,83.6%and 81.8%.4、The statistical results showed that number of native species accounted for 89.6%of the total number of trees.The number of exotic species of shrubs accounted for 11.0%of the total number of shrubs.There was a certain difference between the proportion of evergreen and deciduous tree species.The general trees and shrubs showed the characteristics of fewer evergreen trees and more deciduous trees.5、The Margelf index of urban riparian arbors was ranked as 5th-6th ring road>2nd-3rd ring road>within 2nd ring road>3rd-4th ring road>4th-5th ring road,while the Margelf index of shrubs was ranked as 2nd-3rd ring road>5th-6th ring road>4th-5th ring road>within 2nd ring road>3rd-4th ring road.The Magnelf index,the Shannon Wiener index and the Pielou index of close-to-nature river bank are the largest among banks with different hardening gradients,while the diversity index（except evenness index）of shrub in the vertical dam bank is the largest.6、Individual health index of urban riparian forests in Beijing ranged from 0 to 1,and health grade showed a right-biased normal distribution.The majority of trees were sub-healthy（47.99%）and medium-healthy（40.68%）.The number of unhealthy trees was relatively small（6.79%）,which health index was between 0.0 and 0.4.The number of healthy trees accounted for 4.54%,and health index was between 0.6 and 1.0.7、The health index of 12 tree species with higher application frequency was ranked as Acer elegantulum>Fraxinus chinensis>Sophora japonica>Ailanthus altissima>Populus tomentosa>Populus X canadensis>Koelreuteria paniculat>Robinia pseudoacacia>Broussonetia papyrifera>Pinus tabuliformis>Ulmus pumila>Salix babylonica.8、Health degree of native species in different districts was higher than that of exotic species.The individual health index of deciduous species showed a trend of decreasing first and then increasing with the increase of the distance to the city center.9、The population health index of urban riparian forest in Beijing was 1.12,and the whole health level was moderate.The whole health index decreased first and then increased along the ring roads.There was no significant difference in different grades of rivers（P>0.05）,and the ranking was as follows:first-order river>third-order river>second-order river.10、There was no significant difference in the health index of Beijing urban riparian forest of different hardening riverbanks（P>0.05）.The whole health index showed a trend of decreasing first and then increasing with the decrease of river bank hardening proportion.There were significant difference in different slopes（P<0.05）.The whole health index showed a trend of increasing first and then decreasing with the increase of slope.