Estimating the contribution of community landscape construction to urban carbon neutrality: methodology and database construction

Green ecological communities have garnered significant interest due to their role in providing urban ecosystem services, and community greening plays a pivotal role in urban environmental enhancement. In the context of carbon neutrality-oriented goals, it is imperative to acknowledge the significance of various landscape designs in carbon sequestration within community greening initiatives. However, there is currently a lack of consideration for landscape designs that promote high carbon sequestration in community greening projects. Our research with literature research and experimental measurement data as data sources, established a database of carbon sequestration of 138 common vegetation species in Shanghai. Based on the vertical vegetation structure within landscape design, we propose seven modular planting structures that reflect the carbon sequestration potential of high-capacity plants within different community green spaces. Our findings reveal substantial variations in carbon sequestration among different tree species within arbor and shrub categories, whereas the differences in carbon sequestration among various herbaceous plants per unit area are comparatively smaller. Among the different combination patterns, the highest carbon sequestration is achieved by the vegetation configuration of the three-layer structure pattern, and the combination of arbors, shrubs and grasses can maximize the effective use of space. This study holds significant importance in optimizing the utilization of limited green spaces within communities and enhancing the carbon sequestration benefits of community landscapes. Ultimately, these efforts contribute significantly to Shanghai’s journey toward carbon neutrality.


Introduction
Community greening is an important component of urban greenery, and there is a growing body of research emphasizing the important role of community landscape vegetation in providing urban ecosystem services (Tahvonen andAiraksinen 2018, Haase et al 2019).Jaung et al (2020) found that urban green can reduce air pollution in Singapore, specifically PM 2.5 and PM 10 , by 20% and 40%, respectively.Urban street trees have also been shown to significantly reduce rain runoff (Selbig et al 2022).Furthermore, green vegetation on buildings can lead to a decrease of 1 • C to 3 • C in summer indoor temperatures due to the combined effect of shading and evapotranspiration (Oquendo-Di Cosola et al 2022).Additionally, dense vegetation can increase the absorption coefficient by 0.2-0.3(Attal et al 2021).Moreover, urban green spaces can function as carbon sinks through photosynthesis.However, the amount of carbon sequestration is closely related to the characteristics of plant communities (Liu et al 2018).As cities are striving for being carbon neutral, enhancing carbon sequestration of community landscape vegetation is becoming an emerging critical research topic.
However, there is still academic controversy about the use of community landscape vegetation to enhance carbon sequestration capacity.For example, Uwe and Kirschbaum (2009) argue that carbon storage and sequestration by urban trees is temporary in the long term because carbon storage and sequestration processes are reversible.For example, if trees are cut down or die, carbon storage in urban forests may be reduced.In that, as agreed at the World Forum on Urban Forest (in 2018) it is of paramount importance that critical urban infrastructures require an adequate planning, design, management, maintenance and continuous monitoring.The effectiveness of using temporary carbon storage and sequestration to mitigate climate change has also been questioned.But there are still studies that indicate that human settlements store 10% of the total carbon stored on their land.Of this carbon, 64% is attributed to soils, 20% to vegetation, 11% to landfills, and 5% to buildings (Churkina et al 2010).Plants and soils are natural regulators of atmospheric CO 2 .Plants fix carbon in the atmosphere and carbon is also deposited in the soil for decades (Kuittinen et al 2016).
Moreover, in addition to carbon sequestration benefits, community landscapes have additional ecological benefits that need to be considered in concert with carbon sequestration.For example, Xue and Li (2017) showed that street trees with high leaf area density reduced PM 10 concentrations by 39% on the leeward side and 89% on the windward side.Tang et al (2021) showed that vegetation cover not only regulates soil loss but also responds positively to rainfall depth and intensity.Zeng et al (2022) used an augmented regression tree model to find that vegetation landscape diversity, roughness and fragmentation have a greater effect on urban surface temperature when vegetation cover is dominant.When talking about Yilongwan community in Changzhi City, Yan and Zhao (2013) mentioned three-dimensional greening in terms of landscape construction.Enhance three-dimensional greening such as roof garden and green planting wall.Planting vine plants such as Wisteria sinensis, Campsis grandiflora and Parthenocissus tricuspidata in public areas not only reduces the carbon emission of buildings, but also achieves the effect of sound absorption, heat insulation, water conservation and air purification.Zhao and Zhao (2013) mentioned in the design of low carbon communities that more attention should be paid to the local conditions and the choice of plant configuration patterns in landscape design.In the configuration of plants, one should not just rely on planting trees and grasses to choose blindly, but should make full use of the local natural conditions and resource characteristics to reasonably match arbors and shrubs, deciduous and evergreen arbors, broad-leaved plants and conifers.In summary, vegetation plays an important role in the construction of inner-city community greenery.They play a diversified ecological service function and play an important role in the improvement of the environment.
If the planning of community green spaces ignores the different carbon sequestration capacities of trees and other green infrastructure, this will lead to a possible underestimation of the carbon sequestration potential of urban green spaces.Therefore, this study develops a framework that first quantifies the carbon sequestration and then optimize community landscape vegetation design to maximize the carbon sequestration.In response to the lack of awareness of carbon sequestration in the planning and implementation process of many urban munities, some areas of low carbon sequestration have emerged, resulting in a serious lack of carbon sequestration capacity of green areas.We will carry out specific designs to achieve high carbon sequestration in the community landscape, and through the selection of vegetation and optimization of vegetation combinations in different scenarios, we will build an urban community landscape to improve the carbon sequestration benefits of the community landscape, thus contributing to the carbon neutrality of the city of Shanghai.

Review of vegetation carbon sequestration measurement or simulation methods in community
Accurate measurement of carbon sequestration in community green spaces is instructive for research to enhance the carbon sequestration function of community green spaces and promote low carbon communities.Carbon storage in urban green spaces is commonly regarded as transient due to the vulnerability of vegetation to both natural and human disturbances.It is anticipated that urban green spaces will sequester carbon from the atmosphere over the next 30 years and subsequently release it gradually during the latter half of this century.Therefore, the measurements of vegetation carbon sequestration mentioned below are for short-term carbon sequestration.Carbon sequestration by plants is characterized by the carbon content of stems and leaves in above-ground biomass (AGB) and roots in belowground biomass (BGB).The total carbon content of above-ground and BGB is the total carbon sequestration of a plant (Zaid et al 2018).Many studies have been conducted by domestic and foreign scholars in recent years, and the overall measurement methods can be divided into Field inventory method, Remote sensing inversion, Model simulation, and Flux observation methods.Cai et al (2021) used a forest carbon sequestration model and forest field surveys to find that by implementing effective existing forest management strategies and expanding afforestation, forests have the potential to offset 14.1% of China's national anthropogenic carbon emissions over the 2010-2060 period, making a significant contribution to achieving the 2060 carbon neutrality target.Luo et al (2019) conducted a review of the Chinese 1978-2013 literature on biomass equations and developed a dataset of standardized tree biomass equations in China.Chen et al (2020) used a particle swarm optimization-back propagation algorithm to match and unify DMSP/OLS and NPP/VIIRS satellite data based on remote sensing inversion method to measure the corresponding net primary productivity in districts and counties in China from 2000-2017, and finally the amount of carbon sequestered by terrestrial vegetation was obtained with the help of the conversion coefficients of vegetation dry matter and absorbed CO 2 .Hu et al (2021) assessed the carbon sequestration benefits of red soil areas in the hills of southern China based on the InVEST (Integrated Valuation of Environmental Services and Trade-offs) model with the land use/land cover dataset from 2000 to 2015.Chen (2018) used Google Earth high-resolution imagery to more accurately match green space samples in Chengyang streets of Qingdao, improving the estimation accuracy and deriving the spatial distribution of carbon density in different green space types.Ma et al (2021) used algorithms of i-Tree and kriging interpolation to quantify and map the carbon storage and carbon sequestration capacity of trees in urban forests.Some studies have also used the CITYgreen model to assess the carbon sequestration and oxygen release benefits of urban planted forests (Longcore et al 2004).Gratani et al (2016) analyzed the CO 2 sequestration capacity of vegetation and its economic value in four parks in Rome, based on an open infrared CO 2 gas analyzer (ADC LCA4, UK) and a leaf chamber (Parkinson leaf chamber) to determine the net photosynthetic rate of vegetation.In summary, for the existing methods of calculating vegetation carbon sequestration all have their different characteristics and application scales (table 1).The field inventory method can be accurate to individual tree species and account for regional carbon sequestration through bottom-up calculation, but the workload and calculation process are large and not suitable for rapid calculation of areas with large areas.The remote sensing inversion method can achieve large scale carbon sequestration estimation quickly and in real time, but the results are influenced by the accuracy of remote sensing images and there are uncertainties.The application of the model to calculate vegetation carbon sequestration is affected by the applicability and uncertainty of the model itself and the diversity of driving data.The flux observation method can be the most direct and continuous measurement of CO 2 , which can be applied to different ecosystem carbon fluxes to form a monitoring system.However, the instrumentation is expensive and the construction of supporting facilities is demanding, while the measurement is difficult and requires professional technicians for operation and regular maintenance.In summary, each of these methods has advantages and disadvantages as well as application scales, and in practice it is necessary to combine different scenarios and purposes to choose the measurement method.

Effects of natural factors, artificial factors, and landscape design on carbon sequestration and other ecological benefits
Plant photosynthesis and respiration are not static.They are multiply regulated by vegetation type, soil conditions, climate and environmental factors, and many conditions such as climate, nutrients and water are in a dynamic process, so the carbon storage and other ecological benefits of vegetation are constantly changing.For example, Wang et al (2022) found that climate change may have an important impact on the productivity of marshland vegetation and thus on the regional carbon cycle.An increase in summer and autumn precipitation can enhance the net primary productivity of marsh vegetation, while a rise in mean summer temperature may reduce vegetation's net primary productivity.Precipitation plays a crucial role in increasing carbon sequestration in forests by promoting plant growth, productivity, and biomass (Liu et al 2015).However, in the representative concentration pathway (RCP8.5)scenario, summer precipitation decreases and extends over a longer period.Consequently, vegetation's water demand increases during the growing months, potentially leading to conflicts in water use and reduced future vegetation growth (Li et al 2021).In regions where a favorable combination of hydrothermal factors supports plant growth, there is a larger plant biomass and higher vegetation carbon density.Conversely, in drier regions, precipitation becomes the primary limiting factor for net primary plant productivity (NPP), and NPP declines with decreasing precipitation-topotential-evaporation ratios.Correspondingly, the carbon sequestration capacity of plants decreases with reduced productivity (Wei et al 2022).Yan et al (2022) designed three RCP (RCP2.6,RCP4.5, and RCP8.5) scenarios and discovered that under all If reasonable allocation is made when greening the community, not only can the economic and ecological benefits of building a low-carbon community be enhanced, but also a community with more regional characteristics can be created.Actively introducing native tree species, this method is worthy of wide application and vigorous promotion.In summary, the amount of carbon sequestered by vegetation is influenced by many factors, such as natural factors (temperature, pH, soil conditions), artificial factors (human management activities), and landscape design (age of plants, species type, adaptability).However, for the regional vegetation community landscape design involving a large number of plant species, it is not clear how to improve the overall carbon sequestration effect of community landscape greening plant application configuration.Therefore, we focus on how to combine local natural conditions and landscape characteristics in greening design to maximize the ecological benefits of vegetation, especially to achieve the maximum carbon sequestration benefits under the goal of carbon neutrality in this study.In this paper, we will compare and analyze the carbon sequestration capacity of selected vegetation for community greening of different green space types under the premise of high carbon sequestration capacity, and provide ideas for the formation of vegetation landscape with high carbon sequestration benefits.

Indirect emission reduction and other benefits of community landscape vegetation based on life cycle considerations
In considering the carbon circulation process under the whole life cycle, a large amount of green waste generated from the natural growth or management and maintenance of landscape vegetation in the community, such as: fallen leaves of trees and shrubs, branches, prunings or lawn mowings, discarded flowers and plants in gardens and flower beds, and weeds, etc, unlike forests in the natural environment, will be disposed of through landfills (Ma et al 2022), traditional composting (Xu et al 2021), and other post-processing methods.It has been found that the litter produced by vegetation contributes to the increase of organic matter in soil, which is decomposed by microorganisms over time and directly contributes to carbon sequestration (Dignac et al 2017).Hua et al (2022) also found in a study comparing the ecosystem services of natural forests with those of planted forests that natural forests are more effective than planted forests in conserving three environment-oriented ecosystem services: biodiversity and surface carbon storage, soil conservation, and water harvesting.Therefore, the disposal of vegetation waste (including prunings, litter, and dead plants) can also have an impact on the total carbon sequestration.Some studies mention that urban vegetation waste is collected and transported to landfills, where about 40% of the carbon is sequestered in the long term; whereas carbon in vegetation waste in natural ecosystems is generally largely released in 3 years or even less (Shi et al 2016).Therefore, if the litter and pruning of vegetation in cities are properly treated and disposed, they will contribute more to the carbon sequestration than the litter in natural ecosystems (Wen et al 2010).Reyhani et al (2022) also found that plants can recycle the carbon released during production after 12 or 14 years, and selecting plants suitable for local climatic conditions not only reduces the use of nutrients and irrigation, but also minimize the negative impacts of the operational phase.Marchi et al (2015) found that herbs grow to the end of their lifespan and compost the green waste and add it to the soil.The carbon dioxide absorbed from the atmosphere during vegetation growth is eventually stored in the soil as microbial biomass.Downey et al (2021) also concluded that the interaction between the initial site conditions for plant community establishment and growth increases soil carbon storage.However, it has also been found that the age of the community is actually an important factor affecting soil carbon content, with the accumulation threshold being greatest in older communities over 50 years old (Campbell et al 2014, Sapkota et al 2020).In fact, the general age of communities is less than 50 years, so soil carbon sequestration is usually not considered as a priority when considering the full life cycle of community greening.In addition, forest waste can also be used as a raw material for wood products, which is nearly an effective treatment for extending carbon storage (MacFarlane 2009).In summary, it is suggested that when dealing with community green solid waste, Z Huo et al wood products can be made as raw materials for temporary and effective carbon storage.Alternatively, it can be made into ground cover and biochar for further recycling.In considering the whole life cycle of community greening planning, design, tree planting, management, maintenance and renewal, the carbon cost during the construction period is a one-time cost, while the carbon cost during the maintenance period is accompanied by the whole life cycle of community greening.Therefore, it is crucial to effectively enhance the carbon sequestration capacity of community landscapes in general, and to reduce carbon emissions by rational use of greening solid waste while taking full advantage of the carbon sequestration function of plants.In the discussion section of this paper, we will focus on how to deal with green waste based on the whole life cycle consideration to increase the overall carbon storage capacity of the community.

Total carbon sequestration measured by real measurement method
In measuring the total carbon sequestration in an area, the average standard sample wood method was used to divide the tree species into different layers according to the vegetation configuration: arbors, shrubs and herbaceous vegetation.Using the biomass expansion factor method, tree biomass was measured by substituting the biomass expansion factor (Intergovernmental Panel on Climate Change (IPCC) parameter of biomass expansion factor (BEF)) determined by the IPCC into the biomass equation.In addition, the four carbon pools of AGB, BGB, litter and soil organic matter are usually included when considering the overall long-term carbon storage of an area, but the carbon pools of soil organic matter and litter are not included here because the community landscape is different from the vegetation in the natural environment due to its short existence (less than 50 years) and the extensive artificial care and post-treatment of green waste from the landscape vegetation.The carbon pool of soil organic matter and litter is not included here (based on the whole life cycle, the carbon sequestration of litter will be discussed in the discussion section).Therefore, two carbon pools, AGB and BGB, are mainly considered in the community landscape.Referring to the standard 'Forestry Carbon Sequestration Measurement and Monitoring Technical Regulations' (DB31/T 1234-2020), the specific steps of the algorithm are as follows: (1) Measurement of arbor carbon stocks The carbon stock of the arbor layer is the product of the sum of AGB and BGB of each tree species in the arbor layer and its carbon content, which is calculated in equation (1), where C arbor is the carbon stock of the tree layer (including scattered trees and quadrats), W above i is the aboveground biomass of tree layer i, W below i is the belowground biomass of tree layer i, n is the number of tree species in the tree layer, and CF i is the carbon content rate of tree species i.
Total aboveground biomass of the arboreal layer is calculated in equation ( 2), (2) AGB of the arbor layer in sample plots of forest type i is calculated in equation ( 3), (3) For the AGB of the arbor layer the anisotropic growth equation was used and calculated in equations ( 4)-( 7), (4) Trunk biomass, Branch biomass, Leaf biomass, where D is the diameter at breast height, H is the tree height, S is the area, m is the total number of forest types, n is the number of tree plants in the sample plot, and a and b are constants.
The BGB of the arbor layer was approximated based on the conversion relationship between the below-ground and AGB (root-to-stem ratio).The total BGB of the arbor layer is the sum of the BGB of all arbor types, as shown in equation (8), where n is the number of forest types, A i is the area of forest type i, W above ij is the AGB per unit area of tree layer of tree species j of forest type i, and r ij is the tree rootstock ratio of tree species j of forest type i.
(2) Calculation of carbon stock in shrub layer The sample harvesting method was used to analyze and derive the shrub layer biomass data per unit area.The regional shrub layer biomass is the sum of shrub layer biomass of all forest types or urban green areas in the region (including the biomass of the underground part), and the carbon stock of shrub layer is the product of shrub layer biomass and carbon content rate, calculated in equation ( 9), where n is the number of forest or urban green space types, A i is the area of the ith forest or urban green space type, Wshrubi is the average of shrub layer biomass per unit area of the ith forest or urban green space type, and CF shrub is the carbon content rate of shrub layer. (

3) Calculation of carbon stock in herbaceous layer
The herbaceous layer biomass per unit area was also measured using the sample harvesting method equation ( 10), where n is the number of green space types, A i is the area of the ith green space type, Wgrassi is the average of herbaceous biomass per unit area of the ith green space type, and CF grass is the carbon content rate of herbaceous layer.

Measurement of monoculture carbon sequestration by field measurement
In the measurement of vegetation carbon sequestration, accounting using the model method needs to be determined by the actual measurement method, and in addition the actual measurement can also directly determine the amount of carbon sequestered by some individual plants.
(1) Measurement of plant growth indicators Each tree species was randomly selected to measure growth indexes, including diameter at breast height (D), plant height (H) and crown diameter (R).The diameter of the trunk at 1.3 m above ground level was measured using a tape measure as the diameter at breast height data.Canopy width data were also measured using a field tape measure in the vertical projection, including east-west and north-south directions, and the mean value was taken as the R value; the canopy projection was approximated as a circle, and the canopy coverage area (C) was calculated.
(2) Measurement of photosynthetic rate and leaf area index of plants In this study, the photosynthetic rate of the common urban tree species tested was measured using a portable photosynthesizer (Licor-6400) manufactured by Li-Cor, USA.Three sunny and windless days were selected for each of the three measurements.The measurements were carried out under natural light at 2 h intervals between 8:00 am and 6:00 pm.For each tree species, five healthy and representative individuals were selected each time, and five leaves of good growth, similar in size and sunny side were selected, and three instantaneous photosynthetic rate values were recorded for each leaf, and the average value was taken.In order to ensure the scientific and comparability of the results, all the test trees were measured in one day as far as possible.Individuals measured by the same instrument were kept consistent, and the order of the measured tree species was kept unchanged.The leaf area index was measured by LAI-2000 plant canopy analyzer, and three representative individuals were selected for each plant to take the average value.
(3) Calculation of the average photosynthetic rate and carbon sequestration capacity of plants The total net assimilation of plants on the day of measurement is calculated by equation ( 11), where P is the total net assimilation (total net assimilation from 8:00 to 18:00) on the measurement day (mmol•m −2 •d −1 ), p i is the instantaneous photosynthesis rate at the initial measurement point, p i+1 is the instantaneous photosynthesis rate at the next measurement point (mmol•m −2 •s −1 ), t i is the instantaneous time at the initial measurement point; t i+1 is the time at the next measurement point (h), n is the number of measurements, 3600 indicates 3600 s per hour, and 1000 indicates conversion of 1000 µmol to 1 mmol.The total assimilation on the measurement day was converted to the amount of fixed CO 2 on the measurement day using the equation ( 12), where W CO2 is the mass of CO 2 fixed by the leaves per unit leaf area (g•m −2 •d −1 ) and 44 is the molar mass of CO 2 .
The average daily carbon fixation (g•tree −1 •d −1 ) of the whole plant is calculated by equation (13) as, (13)

The CITYgreen model measures the amount of carbon sequestered by a single plant
Based on its many years of statistical research on plant data and statistical analysis of big data, the US Forest Service developed a calculation system related to plant carbon sequestration, which began to be widely used due to its easy utilization (Peng et al 2008, Yang et al 2022).At present, the ones with higher acceptance are Citygreen calculation system8 .Citygreen is based on GIS and remote sensing technology, and the overall plant cover and carbon sequestration factor are used as the calculation unit with the data of single plants.The specific descriptions are as follows: (1) Calculation principle of CITYgreen model The CITYgreen 5.0 model assesses the annual carbon storage and uptake of plant communities in the study area, which is calculated based on the carbon storage and uptake factors corresponding to the different age classes of plants, with the following equations ( 14) and ( 15 (2) Collection of basic data Collect basic information of trees.The basic information of tree species includes: species name, tree height, tree height growth rate, maximum tree height, diameter at breast height, diameter at breast height growth rate, maximum diameter at breast height, crown size class, leaf sparsity, crown type, leaf abscission.
(3) Digitization of the study area Including loading images, digitization of graphics, updating and analysis of database, and research results.
(4) Output results The data of plant communities in the sample area are statistically analyzed and then input into CITYgreen model for analysis and calculation.Using the carbon sequestration benefit module of CITYgreen model, carbon density (carbon storage per unit area, t•hm −1 ) and carbon sequestration rate (annual carbon reduction per unit area, t•hm −1 •a −1 ) are estimated.The CITYgreen model was used to estimate the carbon sequestration benefits and output the calculation results.
In the database of vegetation carbon sequestration amount compiled in this study, the values of 84 species of vegetation carbon sequestration amount were mainly calculated by CITYgreen model through researching the literature and screening and summarizing; in addition, the carbon sequestration amounts of 54 species of trees actually measured by combining with the standard 'Forestry Carbon Sequestration Measurement and Monitoring Technical Regulations' (DB31/T 1234-2020) were included The final database of carbon sequestration of 138 species of vegetation in Shanghai was formed.

Methodology for monitoring and modeling carbon sequestration benefits under small landscape vegetation combinations
The selection of high carbon sequestration vegetation needs to be properly matched to maximize the carbon sequestration effect.Through a large number of studies, it is found that the vegetation structure with complex community structure and a combination of arbor, shrub and herb layers usually has a strong carbon sequestration capacity; mixed evergreen-deciduous forest has a stronger carbon sequestration capacity than simple evergreen or deciduous forest (Chu et al 2022).The higher the diversity of vegetation in the environment, the more complex the composition and the more layers, the higher the total carbon sequestration capacity of plants in this environment (Chu et al 2022).In the design planting process of this study, we followed the following method to set the planting pattern.Since the general planting spacing of middle-aged trees is 5 m, we set a single module footprint: 15 × 15 m.The plant configuration within the module, and considering different spatial structures, is divided into single arbor, single shrub, and lawn.Combination type: arbor and shrub, arbor and grass, shrub and grass, arbor, shrub and grass.Specific combinations are shown in figure 1.
In the actual design, plants can often be divided into different combinations of structures.Among them, the vertical structure of plant community is the vertical differentiation of the community in space, reflecting the stratification structure of tree species in the community.According to the vertical structure of plant communities, plant community types can be divided into seven types: arbor, shrub and grass, arbor and shrub, arbor and grass, shrub and grass, single arbor, single shrub and single grass.Among them, the arbor, shrub and grass type belong to the three-layer structure pattern, arbor and shrub type, arbor and grass type, shrub and grass type belongs to the two-layer structure pattern, and single arbor, single shrub and single grass belongs to the single-layer structure pattern.Therefore, in the calculation, the combination of each level of vegetation is calculated according to the different structural modes, for example, the total carbon storage in green space of the three-layer structural mode of tree and irrigation-grass type is the sum of the carbon storage of each carbon pool of tree and irrigation-grass, equation ( 16), (16)

Vegetation selection and classification
Species common to Shanghai were selected for vegetation in accordance with the International Code of Botanical Nomenclature.The nomenclature of green plants is organized into 12 major categories.The main taxonomic categories are as follows: Kingdom, Division, Class, Order, Family, Tribe, Genus, Section, Series, Species, Variety and Forma.
In the database, plants can be simply divided into: plant genera and plant species, with species referring to a specific one and species with similar affinities grouped into one genus.Among them, a total of 138 plant species are included belonging to 53 types of families, such as Liliaceae, Cypress  2).

Literature data sources, and selection and calibration
To analyze the carbon sequestration of various tree species in Shanghai, we utilized the WOS and CNKI database as our primary data source.The literature was systematically searched using keywords such as 'plant carbon sequestration' , 'carbon sink' , Large arbors (over 20 m high), medium arbors (10-20 m high), small arbors (3-10 m high), shrubs, herbs Leaf growth characteristics Evergreen broad-leaved arbors, deciduous broad-leaved arbors, evergreen coniferous arbors, evergreen shrubs, deciduous shrubs, bamboo, wet plants, climbing plants, perennial flowers, ground cover plants 'landscape' , 'landscape design' , 'tree species' , 'lowcarbon community' , 'community landscape' , 'community vegetation' and 'ecological benefits' .The search was conducted in October 2021, and after screening the literature without authors and duplicates, more than 100 documents retrieved from WOS and CNKI were used as the sample for analysis, and 84 values of carbon sequestration by vegetation were filtered and summarized by reading the literature.In addition, the amount of carbon sequestered by the 54 tree species actually measured was included during 2018-2020, resulting in a database containing the amount of carbon sequestered by the vegetation of 138 species in Shanghai.Since the units of the investigated vegetation carbon sequestration are not completely uniform, it is not possible to clearly compare the magnitude of the actual carbon sequestration of different vegetation.Therefore, we made a uniform conversion.The units of carbon sequestration of trees and shrubs were expressed as kg•tree −1 •yr −1 , and those of herbaceous vegetation were expressed as kg•m −2 •yr −1 .In the surveyed data, the raw carbon sequestration units are expressed in terms of g•m −2 •d −1 and g•tree −1 •d −1 .Therefore, the conversion was carried out by combining the canopy size of single trees with the actual photosynthetic days, for deciduous arbors and deciduous shrubs, the daily carbon sequestration in ground area was taken as the average value.Considering that deciduous vegetation has little or no carbon sequestration capacity in winter (Sarma et al 2022), we assume that only the carbon sequestration in spring, summer and autumn is considered, and the number of days in these three seasons in China is about 274 d.Thus, the conversion is based on carbon sequestration of about 274 d per year, while for evergreen trees and evergreen shrubs, the conversion is based on carbon sequestration of 365 d per year.

Experimental instruments for the measured data
For the actual measurement data of tree carbon sequestration, the experimental instruments and tools used are, portable photosynthesizer (Licor-6400), LAI-2000 plant canopy analyzer, tape measure, chest gauge, height gauge, etc produced by Li-Cor, USA.The measured data were calculated using Excel and Origin.

Database construction and result analysis
After aggregation and calibration, a database with uniform units was finally formed to facilitate comparison of the magnitude of vegetation carbon sequestration.Each attribute contained in the database is described in table 3, and it is noteworthy that some species exhibit variations in growth forms according to different habitat conditions.For the given species, we used the growth forms that first appeared in the descriptions in the authoritative Flora of China (Editorial Communitte of Chinese Botany 2019).For example, Pittosporum tobira in Flora of China is depicted as an evergreen shrub or small arbor, up to 6 m tall, with leaves aggregated on the tops of branches, biennial, and leathery.Therefore, it is listed as an evergreen shrub in our database.After establishing a database on the amount of carbon sequestered by common vegetation in Shanghai, we validated all species names against three authoritative botanical papers: the Flora of China (Editorial Communitte of Chinese Botany 2019), the Plant List (accessed 25 March 2022; www.theplantlist.org/) and the Life China 2019 Annual List (released in Beijing in May 2019; www.sp2000.org.cn/).In the database, different colors are used to distinguish the trees according to their growth types.The tree species in the database are common tree types in Shanghai, containing 138 species of vegetation, 54 families and 103 genera.There are 77 species of trees, 37 species of shrubs, and 24 species of other vegetation (including climbing, persistent flowers and ground cover).Among them, there are 50 species of evergreen vegetation and 72 species of deciduous vegetation according to the classification of the physiologicalecological characteristics of plant leaves adapted to the environment.In addition, for each vegetation, there are vegetation morphological parameters under the corresponding size of that carbon sequestration, such as the size of diameter at breast height, height and crown width.According to the characteristics of ecological habits of various vegetation, the ecological characteristics of each species are classified by referring to the classification of ecological habits of tree species in 'Environmental Landscape-Greenery Planting Design' , and here they can be divided into: shade-tolerant, drought-resistant, saline-tolerant, cold-tolerant, wind-resistant, with strong dust retention ability class, ornamental, fragrant flowering, and bird attracting class.In the database, tree species are marked with a '1' if they have a distinctive ecological habit, a '0' if they do not have that ecological habit at all, and a blank if they are in between.In addition to the economic costs that must be taken into account during the actual construction of a community, the database also contains the latest quotations for each tree species in 2022 (www.yuanlin.com/mmbj/) for specific specifications from the China Garden Network as a reference.The properties of each field in the database are described in table 3.

Comparison of monoculture vegetation
According to figure 2 when comparing the amount of carbon sequestered by individual vegetation.However, when comparing the amount of carbon sequestered per unit land area, arbors did not far exceed shrubs, mainly because of their tall morphology.Among the other vegetation (including climbing, perennial flowers and ground cover types), the carbon sequestration amount in figures 2(a) and 3(c) is smaller than that of arbors and shrubs, and the annual carbon sequestration amount per unit area is less than 2 kg•m −2 •yr −1 and most of them are about 0.5 kg•m −2 •yr −1 .Therefore, the selection of ground cover vegetation can be freely combined with other conditions such as easy survival, easy maintenance and low economic cost of vegetation.Combining the analysis with the classification of physiological and ecological characteristics of plant leaves adapted to the environment, figure 2(d) shows that in the database evergreen arbors account for 18.18%, deciduous arbors for 39.39%, evergreen shrubs for 15.91%, deciduous shrubs for 14.39%, and other (including climbing, perennial flowers and ground cover types) vegetation for 12.12%, according to figure 2(b).The median annual carbon sequestration per unit area was found to be greater for evergreen arbors than deciduous arbors, and for evergreen shrubs than deciduous shrubs.Based on the comparison results of the classification of vegetation ecological habit characteristics, we found that, figure 2(c), overall, the annual carbon sequestration per unit area of vegetation under any ecological habit is greater for trees than for shrubs than for other vegetation such as ground cover plants.Among them, the maximum value of annual carbon sequestration per unit area of vegetation in the classification of shade-tolerant, salinitytolerant, wind-resistant, and strong dust retention capacity is about 10 kg•m −2 •yr −1 .Checking the database, we found that this vegetation is F. chinensis.In addition, a cluster analysis of the carbon Z Huo et al  group green space, residential green space, matching public construction green space, residential road green space, green building planting and roof greening.According to the different requirements of vegetation selection in different areas, for example, the design of group green space should pay attention to summer shade and winter light, so it is appropriate to choose tall deciduous arbors.In addition, multilayered plants should be planted between places and residences for isolation to reduce the impact on the surrounding environment.According to its basic requirements, the configuration of green space in the group should increase the proportion of deciduous arbors and eventually form a multi-layered design with a combination of arbors, shrubs and grasses; the design of residential green space should pay attention to the combination of arbors, shrubs and grasses in the form of plant community configuration.Shrubs should be mainly evergreen plants, supplemented by deciduous shrubs.In addition, the proportion of deciduous arbors should not be less than 50%.The design of shrubs should increase the proportion of evergreen shrubs and eventually form a doublelayer structure combining arbors + shrubs and arbors + grasses or shrubs + grasses; the design of matching public construction green space should pay attention to the desirability of planting tall evergreen arbors.In addition, the proportion of flowering and Based on the vegetation configuration of each type of green space in table 4, a category of arbors and shrubs with high carbon sequestration capacity was selected to calculate the total carbon sequestration of the modules, and the range of high carbon sequestration for different pattern classifications under different configurations designed was obtained.The module area is 225 m 2 , and each module is designed to plant 9 arbors and 9 shrubs per module on average (edge as well as vertex averaging).Since the carbon sequestration of grass is smaller compared with that of arbors and shrubs, the area loss of planting trees and shrubs is ignored, and the lawn area is considered as 225 m 2 , and the calculation results are shown in table 5.
From the calculation results, it can be found that the highest carbon sequestration is achieved by the vegetation configuration of the three-layer structure mode, and the combination of arbors, shrubs and grasses can maximize the effective use of space and achieve the maximum carbon sequestration of vegetation, which is much higher than the carbon sequestration of the vegetation configuration of the single-layer structure mode.In addition, the final carbon sequestration amount varies significantly when different vegetation species are selected, up to 12.19 kg•m −2 •yr −1 .However, in the actual design, it is necessary to consider the diversity of tree species as well as the landscape requirements, especially the community landscape design requires high aesthetics, so it is impossible to choose to plant only single species of trees or shrubs, but our calculation results give a threshold value of carbon sequestration for selecting vegetation in a class of tree species under a high carbon sequestration scenario.It can give some reference in the actual design.

Discussion
The impact of community landscapes on indirect carbon reduction and whole life cycle carbon reduction of buildings, energy use, etc and direct increase in carbon sequestration is not considered in our database.This discussion will add this section and further discuss the significance and contribution of community landscape construction to urban carbon neutrality.According to the data obtained from the above research, considering the physiological characteristics of various tree species, in order to achieve carbon neutrality in cities as soon as possible, the following suggestions are put forward: (1) under the premise of ensuring the abundance and suitability of urban tree species, plants with strong carbon sequestration ability should be selected as far as possible, such as C.
Z Huo et al camphora and S. sebiferum should be selected as far as possible for trees, and P. tobira should be selected as far as possible for shrubs; (2) make full use of the vertical space of the green area, arrange according to the community structure of "grasses + shrubs + trees" from the bottom to the top, maximize the use of the limited land resources of urban greening, and improve the carbon sequestration capacity per unit area.In addition, from the description of urban structure relationship, it is believed that contemporary urban land development is mainly reflected in the construction of communities, which are the cells of urban structure, and community structure and density play a key role in urban energy renewal and CO 2 emission.Therefore, as the most basic application scenario to achieve the goal of 'carbon neutrality' , the green and sustainable development of communities is crucial, and the increase of carbon sequestration through the landscape design of communities plays an important role in the realization of low-carbon or even zero-carbon communities, and it is important to achieve carbon neutrality of urban communities as a whole.

Rational treatment of green waste increases carbon sequestration
Greening waste refers to the dead branches, fallen leaves, grass clippings, flowering debris, tree and shrub cuttings and other plant residues produced by the natural withering of plants or artificial pruning.
With the continuous increase of urban greening rate, the greening area continues to increase.According to the Shanghai Statistical Yearbook released by the Shanghai Bureau of Statistics in 2021 (https:// tjj.sh.gov.cn/tjnj/index.html),by the end of 2020, the greening coverage of Shanghai's built-up areas reached 46 191.72 hm 2 , the greening area of builtup areas reached 44 307.41 hm 2 , and the per capita park green space reached 8.5 m 2 .The accompanying greening waste generation has increased dramatically and has become one of the main components of solid waste.Gong (2014) has found that the average value of garden waste production per unit of urban green space area calculated according to different classifications in different regions is 1-1.5 kg•m −2 .Based on this, with reference to the Shanghai Statistical Yearbook 2021, the green space area in Shanghai in 2020 is 164 611 hm 2 , and the estimated green waste production in Shanghai in 2020 is between 1646 400 and 2469 200 t.Facing the goal of achieving lowcarbon construction, the use of green waste to produce biochar and organic mulch is showing a superior position (Webber et al 2022).Generally speaking, the main components of waste generated in different seasons are different, with pruning waste dominating in spring and autumn, grass in summer and dead branches and leaves in winter (Liu et al 2023).
High quality waste such as tree trunks are collected for organic mulch production to decorate the community, achieving a combination of landscaping and resourceful use.In addition, the production of green waste into long-lasting innovative wood products, such as cross-laminated timber and rigid low-density wood fiber insulation panels, has been widely used as an alternative to steel and concrete in high-rise building systems (Cetiner and Shea 2018).Compared to paper, these innovative products for building and household applications can store carbon for long periods of time.Based on whole life cycle considerations, they can play an important role in increasing the amount of carbon sequestered by vegetation.It has been shown that if green waste is re-produced into innovative composite products for building and household applications, the average annual carbon storage will increase by 26.9%, extending the carbon storage time by about 50 years (Li et al 2022).In summary, proper green waste disposal methods and rational use of green waste will directly increase the amount of carbon sequestered by vegetation under the whole life cycle.This is important for the construction of low-carbon communities and the achievement of urban carbon neutrality goals.

Conclusion
Community landscape architecture is an important component of urban green space and has significant value and potential for increasing carbon sequestration in high-density urban spaces.This paper not only reviews the current methods and applicable conditions for quantifying the amount of carbon sequestered by vegetation, but also explores the effects of natural factors, artificial factors, and landscape design on carbon sequestration and other ecological benefits of vegetation.Through literature research and data calibration, a database of carbon sequestration of 138 common tree species in Shanghai was obtained, which is the basis for selecting high carbon sequestration vegetation for low carbon community landscape design.In addition, this paper designs the landscape construction model of modular low-carbon communities and calculates the range of carbon sequestration under different structural patterns of high carbon sequestration vegetation combinations.This paper also explores the indirect carbon sequestration of green waste in different treatment and disposal methods based on a whole life cycle perspective, with the main objective of drawing attention to the role of this carbon sequestration in maximizing the carbon sequestration benefits of vegetation.
The content of this study will form the basis for future community planning and implementation to achieve greater carbon sequestration benefits.As a basic unit of urban construction, communities can contribute to low-carbon construction and carbon neutrality in cities from the community level.It helps to promote green and low-carbon development and achieve the goal of carbon peaking and carbon neutrality.
the current year = carbon uptake factor×vegetation cover ×area ofstudy area

Figure 2 .
Figure 2. Comparison and distribution of vegetation carbon sequestration (a) distribution of carbon sequestration size per unit area with single vegetation trees and shrubs, (b) distribution of carbon sequestration size under the classification of vegetation foliage growth, (c) distribution range of carbon sequestration of trees, shrubs and other vegetation under the classification of vegetation ecological habit, (d) percentage of vegetation in the database under the classification of vegetation foliage growth.

Figure 3 .
Figure 3. Results of cluster analysis of vegetation carbon sequestration (a) results of tree clustering, (b) results of shrub clustering, (c) magnitude of carbon sequestration of other vegetation.

Figure 4 .
Figure 4. Elevation performance of different vegetation configurations.

Table 1 .
Measurement methods of vegetation carbon sequestration.

Table 2 .
Vegetation classification information table of carbon sink database.

Table 3 .
Introduction to each database property.
Berberisthunbergii, which is only 0.035 kg•m −2 •yr −1 .It can be found that arbors are much larger than shrubs −1 yr −1 , and the smallest is Rosa hybrida, which is only 0.07 kg•tree −1 yr −1 ; under the ranking of annual carbon sequestration of vegetation per unit land area, the largest is still M. bealei, which can reach 8.24 kg•m −2 •yr −1 , and the smallest is

Table 4 .
Recommended vegetation configuration for each type of green space.

Table 5 .
Range of modular carbon sequestration under different combination types.

The importance and significance of establishing a database of carbon sequestration by Chinese native vegetation
The carbon sequestration capacity of different species of plants may vary widely.With their carbon sequestration data, cities can plan and construct urban green space more rationally and accurately, and play the role of vegetation in carbon sequestration efficiently.

5.1. The significance and contribution of community landscape construction to urban carbon neutrality
In response to global climate change, China has made a commitment to achieve carbon peak by 2030 and carbon neutral by 2060 (Xinhua Net 2020).Cities are the core places to achieve green and low-carbon development(Qiu et al 2021).The community, as the basic unit of the city, is the main place where people work, live and reside, and is an important spatial carrier for the city to practice the concept of low carbon, and is also one of the important parts of the construction of low carbon society (Drew-Smythe et al 2023).