Study On Carbon Storage Of Urban Forests In The Context Of Cognitive Preference

The urban forest plays a decisive role in adjusting the climate and improving the city atmosphere environment,and is the important foundation condition that a city relies for existence and develops.And studies have shown that more than 80 percent of global carbon dioxide emissions are mainly come from urban areas,although the city areas are account for 2.4 percent of the global land areas.Therefore,the study on carbon cycle of urban forest has been being the focus both at home and abroad.And the current researches on urban forest are mainly focus on the aspects of its planning,designing and ecological benefits.while the researches about the current situation of the urban forests'planning and using are still little,and the design of the current urban forests are mainly by the designers,and little consideration is given to the users.Therefore,it is very important to optimize the community structure of the urban forests by giving full play to the multiple subjects,and it also plays an important role in improving the urban forests'ecological benefits.Based on the survey of the"city-suburb"sample in 2017,and refers to some analysis of the vegetation about the same area.and makes a further comparative analysis about the structural factors of the urban forest.And finally,three groups of characteristics which are relatively different were selected.and based on those characteristics,we produced a questionnaire,which is designed to explore the urban residents'cognitive preference and participation consciousness of the existing urban forests.And then a discussion about urban forests'high carbon storage models is given,which is based on residents'cognitive preference.Combining the data of questionnaire survey and field survey,the conclusions are as follows:(1)Based on the questionnaire survey,it can be seen that urban residents are mainly tend to a form,which is composed of evergreen forest,low density and multi-layer structure.(2)Based on the structural analysis of three groups of plant communities in the"city-suburb"transect of Shanghai,we can see that the composition and structure of species in urban and suburban within study area showed some differences:there are62 species of trees in the urban area,which are belongs to 49 genera,35 families;and there are 58 species of shrubs belonging to 53 genera and 39 families in suburban areas.The number of species and the proportion of trees and shrubs in urban,and suburban regions have significant differences.Cinnamomum camphora has an absolute advantage in urban and suburban regions,Metasequoia glyptostroboides ranked second;and shrubs are mainly consist by Chimonanthus praecox,Buxus sinica ssp.sinica var.parvifolia,etc.In terms of the composition of vegetation types in the"city-suburb"transect in Shanghai,the study area is dominated by evergreen broad-leaved forest.From the comparison of the vegetation types between the city and the suburbs,we know that the urban area is mainly composed of evergreen broad-leaved forests,and the suburban is mainly composed of deciduous forest.In terms of the hierarchical structure of plant community,based on the survey of the"city-suburb"transect,the distribution of the compound forest is more than that of the single-layer forest.what's more,the species diversity and the combination of the trees,irrigations and grasses are better than that of the single-layer forest.The urban area is mainly composed of double-layer forest and the suburb is mainly single-layer forest.Based on the analysis of the community density characteristics of the transect zone,the low-density communities are dominant,and the vegetation density of the urban areas is lower than that of the suburban areas.But the vegetation coverage in the suburbs is greater than that in the urban areas.(3)The analysis of the carbon sequestration benefits,which is based on the residents'cognitive preference,shows that,The evergreen forests(150.01Mg C)>The deciduous forests(74.57Mg C).The multiple layer forests(143.91 Mg C)>the single layer forests(80.67 Mg C).In terms of density,low density(91.46 Mg C)>high density(73.78 Mg C)>medium density(59.34 Mg C).And based on the average carbon density of each scene,the results showed that:the evergreen forests(33.83 Mg C/hm~2)>the deciduous forests(30.65 Mg C/hm~2);The single-layer forests(35.77 Mg C/hm~2)>the multi-layer forests(28.71 Mg C/hm~2).The high-density forests(54.35 Mg C/hm~2)>the medium-density forests(30.49 Mg C/hm~2)>the low-density forests(11.87 Mg C/hm~2).Based on the residents'cognitive preferences,the combined analysis shows that the scenario 6's proportion of carbon storage is the largest,because it is the most numerous.However,if we based on the average carbon storage and the carbon density of the scenarios,we find that,the values of the low-density forests are lower than that of other combinations.Under the same vegetation composition and community density,the average carbon storage and the carbon density of the multi-layer forests are higher than that of the single-layer forest,which is on the premise of the low-density forests or the medium-density forests.And if we under the same community density and the same layered structure,the average carbon storage and the carbon density of the evergreen forests are higher than that of the deciduous forests;what's more,if we under the same vegetation types and the same layered structure,the average carbon storage and the carbon density are positively correlated with the vegetation density.