Urban Intensity Research Articles

Discover the desirable landscape structure for mitigating urban heat: The urban-rural gradient approach for an ancient Chinese city

Urban heat is one of the most prominent challenges of urbanization. The nature of extraordinarily spatially heterogeneous landscape in cities may provide nature-based solutions to solving the urban heat problems. Here we aimed to discover the most desirable landscape structure vividly demonstrated in urban areas that we can adopt for heat mitigation. We conducted our study in Xi'an, an ancient capital of China, using land surface temperature (LST) retrieved from Landsat8, landscape features interpreted from SPOT6 along with the urban-rural gradient. We found that large LST variability (as high as 18.11 °C) existed within the same urban intensity (UI) and it is very promising to see that potential of heat mitigation broadened with increasing urbanization. This is very likely thanks to the archaic urban design of Xi'an, which incorporates and preserves the wisdom of the ancients in the urban landscape layout. We revealed two landscape composition associated desirable cooling landscape structure models (i.e., the enhancement of blue spaces and the enhancement of green spaces) generally applicable for all urban environments, and three landscape configuration related desirable cooling models, that are the complex grey infrastructure model, the aggregated green space model, and the connected and regular model of both grey and green infrastructures, which can be exquisitely adopted at low, high and intermediate urban intensity gradients.

Riverine dissolved organic matter (DOM) as affected by urbanization gradient

Rapid urbanization has considerably altered carbon biogeochemical cycle and river hydrology. However, the influences of urban land use and urban-induced nutrient increase on dissolved organic matter (DOM) characteristics are poorly understood. Here we hypothesize that the alterations significantly change sources and levels of DOM in river systems that drain the urban areas. To test the hypothesis, we investigated DOM in headwater rivers with varied urban intensities in the Three Gorges Reservoir Area (TGRA), China, through field sampling conducted in the dry and wet seasons. We found positive relationships of urban land (%Urban) with DOC concentration and chromophoric DOM (CDOM) absorption coefficients a254, a280 and a350, as well as fluorescence index (FI370), indicating the significantly increased levels of DOM and autochthonous sources along an urbanization gradient. A stepwise regression analysis demonstrated that occurrences of DOC and CDOM can be predicted by %Urban, while increasing autochthonous source is predictable by the increase in riverine nitrogen. Moreover, a254, a280 and FI370 values showed distinct seasonal variations, with significantly higher CDOM concentration in the wet season and with much higher autochthonous signal in the dry season with high nitrogen loading. Based on the findings, we conclude that urbanization influences occurrences and sources of DOM, with increasing urbanization making an important and direct contribution to DOM, and an indirect effect of urban induced nutrient enrichment, i.e., enhanced nutrient loadings increase autochthonous DOM production in rivers.

Traffic restrictions during the 2008 Olympic Games reduced urban heat intensity and extent in Beijing

Satellite thermal remote sensing has been utilized to examine the urban heat dynamics in relation to the urban traffic restriction policy. During the 2008 Olympic Games in Beijing, the traffic volume was approximately cut off by half through the road space rationing. Based on daily MODIS satellite thermal observations on the surface temperature, statistical models were developed to analyze the contribution of traffic volume reduction to the urban heat intensity and spatial extent. Our analyses show that cutting off half of the traffic volume has led to a marked decrease in the mean surface temperature by 1.5–2.4 °C and shrinkage of the heat extent by 820 km2 in Beijing. This research suggests that the impact of urban traffic on heat intensity is considerably larger than previously thought, and the management of urban traffic and vehicle fossil fuel use should be included in the future urban heat mitigation plan.

The Main Factors and Trends of Urbanization in Kazakhstan: Analysis and Recommendations

With the development of industry, the industrialization of agriculture, the strengthening of Industry 4.0 trends in all countries of the world, the trends of migration of rural residents to cities, and the pace of urbanization are increasing. The purpose of the article was to study the main factors determining the trends, intensity, and specificity of urbanization processes in Kazakhstan. The methods of retrospective analysis, analogies, logical analysis, generalizations, demographic and economic statistics, index, graphic, comparative analysis, absolute and relative indicators of demography and migration, methods of the theory of differentiated urbanization are used. Specific methods were applied to calculate the coefficients of urbanization intensity. To achieve the goal, a comparative analysis of theoretical views on trends and factors of urbanization was carried out. Based on statistical data, a comparative analysis of the birth rate, the level, and quality of life, the level of poverty in cities and villages of Kazakhstan was carried out. The dynamics, orientation, and territorial distribution of urbanization processes are revealed. To determine the hierarchies of cities depending on the population, Zipf curves were calculated, ranking of cities was carried out. It is concluded that the processes of urbanization in the country are uneven, as well as that the factors of urbanization are fully manifested in Kazakhstan’s conditions and determine its trends and intensity. Based on the identified trends and problems of urbanization, recommendations on the choice of the main directions and mechanisms for regulating the processes of urbanization in Kazakhstan are substantiated.

Urbanization and water quality dynamics and their spatial correlation in coastal margins of mainland China

The urbanization of coastal margins and the resulting deterioration of coastal water environment have been a major concern, due to their substantial threat to the health and sustainability of coastal marine ecosystems. However, the spatiotemporal information about these two aspects and their correlation analysis are still lacking in China. This study quantitatively investigated the urbanization and water quality dynamics from 54 statistical units of coastal margins with a width of 40 km in mainland China, and examined the response characteristics of different water quality indicators to the coastal margin urbanization (CMU). Our results revealed that CMU generally shifted from low to medium/high levels nationwide in 2000–2013, with a 75% increase in the average urbanization index, while the nearshore water quality did not vary significantly over time, maintaining a medium level in the sequence of water quality from good to bad during the study period. The spatial heterogeneity of CMU and water quality distribution was evident. Yangtze River Estuary, Pearl River Estuary, Hangzhou Bay, Bohai Bay and the coastal provinces located here, including Shanghai, Tianjin, Zhejiang, and Guangdong, should receive more attention due to their excessive CMU and the worst coastal water quality. The indicators that characterize the overall state and eutrophication of water quality were found to be sensitive to CMU. Compared with coastal cities, coastal margins were stronger in terms of urbanization intensity and impact on coastal water quality. The findings will provide basic scientific information for decision-making on urbanization control and ecological restoration in coastal margins, and will also promote the understanding of the CMU process and its environmental impact from a continental-scale perspective.

A Comparison of Springtime Pollen and Nectar Foraging in Honey Bees Kept in Urban and Agricultural Environments

Spring is an essential time for honey bee foraging in temperate climates. This is a period of increased brood rearing supporting colony growth and demands access to high-quality pollen and nectar resources. With the expansion of urban and agricultural landscapes, the availability of pollen and nectar producing flowers is declining in many areas. We aim to determine how patterns of spring pollen and nectar foraging differ between colonies surrounded by varying degrees of urban and agricultural intensity, as well as to assess the potential for nectar sampling to serve as a proxy for pollen collection. Thirteen apiaries in Central Ohio, along a gradient of urban and agricultural intensity, were monitored in spring of 2019 through the periodic collection of pollen and nectar samples and continuous colony weight monitoring. We found that spring honey bees in urban and agricultural areas gain comparable amounts of weight and use similar spring resources. Foraging was heavily focused on flowering trees and shrubs including Malus (apple), Salix (willow), and Prunus (cherry), until the beginning of clover bloom (Trifolium spp.). We also identified differences in pollen and nectar foraging within colonies, with nectar containing fewer species collected more evenly than matched pollen samples. These results demonstrate that honey bees in both agricultural and urban environments exhibit similar foraging patterns during the spring, and that plant species important for nectar collection are substantially different from plants important for pollen foraging, though limitations in nectar collection hinder our ability to draw definitive comparisons of pollen and nectar foraging in this region.

Urbanization Processes in the Steppe Krai and Turkestan (late 19th – early 20th Centuries)

At the beginning of the 20th century, the processes of urbanization were actively taking place in the Russian Empire, but in different regions they went with varying degrees of intensity. Modernization changes in the traditional agricultural and nomadic societies of the Central Asian region began after its final annexation to the Russian Empire, which happened quite late – in the 60-70s of the 19th century. Based on the data of statistical surveys of the Steppe and Turkestan general-governorate’s areas, the authors analyze the urban population’s dynamics, the movement of its class and national composition in order to assess the level of urbanization of the region, as to what extent it reflects the general patterns of modernization and what is its regional specificity. The graphs compiled according to the Surveys show that in all nine areas of the region there was a quantitative increase in the urban population. The main incentives for urban growth were trade and railway construction. At the same time, another trend is observed: the proportion of citizens in the entire population does not increase significantly, but fluctuates in the range of several percentage points. The absence of pronounced dynamics of the urban population outpacing growth over the rural population indicates the initial stage of the Central Asia’s urbanization. The low intensity of urbanization is quite corresponded to the Central Asian economic modernization imperial strategy, which consisted in the development of commodity specialization of agricultural sector for the needs of the metropolitan industry and peasant colonization of the region.

Variation in ecosystem services of street tree assemblages can guide sustainable urban development

Abstract Urban afforestation is an important strategy for promoting sustainable urban development. In cities where large new green spaces are not available, the planting of curbside trees is deemed to be an important afforestation strategy. However, variations in the ecosystem services provided by street tree assemblages across socioeconomic gradients have been unexplored. We examined such variations in ecosystem services provided by street tree assemblages along an urban–suburban continuum. Our findings were as follows. (i) Not all ecosystem services showed increasing trends along the urban–suburban continuum. Some ecosystem services at the street tree assemblage level, such as air purification and rainfall interception were prominent in areas of high urbanization intensity. (ii) Diverse ecosystem service trends were found in relation to differential characteristics of street trees assemblages. Structural properties of street tree assemblages, such as tree density and age structure, are likely key factors influencing variations. (iii) Although street tree density could partially compensate for the loss of large old trees, the protection of such trees is important because of their close associations with key ecosystem services, such as total carbon storage. To maximize the value of street trees in promoting urban sustainable development, trade-offs among multiple ecosystem services should be integrated within the overall planning process and adjustments of planting regimes.

Effects of Urbanization Intensity on the Distribution of Black Carbon in Urban Surface Soil in South China

Rapid urbanization causes the accumulation of large amounts of pollutants, including heavy metals, organic pollutants, and black carbon (BC). BC is the carbonaceous residue generated from the incomplete combustion of fossil fuels and biomass. It plays an important role on the migration of heavy metals and organic pollutants, as well as soil carbon sequestration. BC accumulation due to human activities greatly affects the global carbon budget, helps to drive climate change, and damages human health. To date, few studies have examined how the intensity of urbanization affects the distribution of BC in soils in urban areas. Therefore, the objective of this study is to determine the effects of urbanization intensity on the spatial distribution and content of BC in urban surface soil. We collected samples from 55 sites in South China and used a multi-scale geographical regression model to evaluate the impact of the interference intensity of urbanization on the amount and distribution of BC. Our results showed that the BC content was significantly higher in urban areas (9.74 ± 1.18 g kg−1) than in rural areas (2.94 ± 0.89 g kg−1) and that several urban parks with a higher interference intensity were hotspots of BC accumulation, suggesting that urbanization promoted BC accumulation. Our model revealed that road density was significantly and positively correlated with BC accumulation. Because there are more cars driving in areas with high road density, vehicle emissions may be one of the causes of BC accumulation. Our results also indicated that the impact of urbanization intensity on the BC distribution was sensitive to sampling density.

ЯЗЫКОВОЕ СОЗНАНИЕ ГОРОДСКОГО НАСЕЛЕНИЯ ДАГЕСТАНА

t. The increased interest in the position of national (native) languages in the world space is due to the intensification of the processes of globalization and, along with it, urbanization; the formation of an information society, which itself determines the dominant language that is necessary for communication. The growth of the importance of one language naturally contributes to the weakening of the status of other national languages, the narrowing of the areas of their functioning, respectively, the transformation of linguistic consciousness and human behaviour. The Republic of Dagestan is a multilingual region in which many national languages and dialects function. The intensity of modernization and urbanization has a huge impact on ethno-linguistic processes, the formation of a certain linguistic consciousness and the resulting linguistic behaviour. Therefore, the study of the state and status of the national language not only as a key identifier of the ethnic self-identification of an individual and a means of communication, the linguistic consciousness of the urban population, their preferred language of interpersonal communication, attitude to the native language of their ethnic community, the influence of the media on linguistic consciousness seems to be relevant in the mainstream ethnolinguistic processes, which are very difficult in a multinational community. Empirical material shows that complex ethnolinguistic processes are taking place in the modern urban space; there is a decrease in the weight of national (native) languages with an increase in the importance of the Russian language. It has been established that there is a transformation of the linguistic consciousness of the urban population, preference is given not to the national (native) language, the priority is communication in Russian.

Predator-Prey Dynamics Are Decoupled in the Raptor Community in a Large Urban Forest

Predator-prey dynamics are fundamental in shaping and regulating wildlife communities; however, these relationships are often altered by urbanization. An urban predation paradox, where predation rates are lower in urban areas despite an increase in predator abundance, has been observed in some predator communities. We looked for evidence of an urban predation paradox in a raptor community in a large urban forest fragment in north Texas, USA. From May–August 2019, we conducted weekly raptor surveys and deployed prey mimics along an urban-to-rural gradient within the forest fragment. We examined relationships between predation rates on mimics, predator abundance, and urbanization intensity using a variety of statistical tests. We detected 161 raptors representing eight species and found that raptor activity was significantly higher in our low urbanization sites. Of the 732 prey mimics deployed, 61 were attacked, and we found no relationship between predation rates and urbanization. Furthermore, we found no relationship between raptor activity and depredation events. Although we failed to find evidence for an urban predation paradox, our results showed a decoupling of the relationship between the abundance of predators and prey in this urban setting. The use of prey mimics is a useful tool for assessing predator-prey dynamics, and more research is necessary to fully understand the impacts of urbanization on this important ecological process.

Spatiotemporal Patterns and Driving Force of Urbanization and Its Impact on Urban Ecology

Urbanization inevitably poses a threat to urban ecology by altering its external structure and internal attributes. Nighttime light (NTL) has become increasingly extensive and practical, offering a special perspective on the world in revealing urbanization. In this study, we applied the Normalized Impervious Surface Index (NISI) constructed by NTL and MODIS NDVI to examine the urbanization process in the Yangtze River Delta (YRD). Geographical detectors combined with factors involving human and natural influences were utilized to investigate the drive mechanism. Urban ecology stress was evaluated based on changes in urban morphological patterns and fractional vegetation cover (FVC). The results showed that the NISI can largely overcome the obstacle of directly coupling NTL data in performing urbanization and has efficient applicability in the long-term pixel scale. Built-up areas in the YRD increased by 2.83 times during the past two decades, from 2053.5 to 7872.5 km2. Urbanization intensity has saturated the city center and is spilling over into the suburbs, which show a “cold to hot” spatial clustering distribution. Economic factors are the primary forces driving urbanization, and road network density is becoming essential as factor that reflects urban infrastructure. Urban geometry pattern changes in fractal dimension (FD) and compactness revealed the ecological stress from changing urban external structure, and internal ecological stress was clear from the negative effect on 63.4% FVC. This impact gradually increased in urban expanded area and synchronously decreased when urbanization saturated the core area. An analysis of ecological stress caused by urbanization from changing physical structure and social attributes can provide evidence for urban management and coordinated development.

Quantifying Spillover of an Urban Invasive Vector of Plant Disease: Asian Citrus Psyllid (Diaphorina citri) in California Citrus.

Urban environments frequently play an important role in the initial stages of biological invasions, often serving as gateways for non-native species, which may propagate to nearby natural and agricultural ecosystems in the event of spillover. In California, citrus trees are a dominant ornamental and food plant in urban and peri-urban environments. We studied the invasion dynamics of the Asian citrus psyllid (Diaphorina citri), which became widespread in urban areas of southern California starting in 2008, to understand the factors driving its more recent invasion in commercial citrus groves. Using a multi-year monitoring database, we applied a suite of models to evaluate the rate at which groves accrued their first D. citri detection and the cumulative number of detections thereafter. Grove characteristics and landscape context proved to be important, with generally higher invasion rates and more cumulative detections in groves that were larger, had more edge, or had more perforated shapes, with greater urbanization intensity favoring more rapid invasion, but with inconsistent effects of distance to roads among models. Notably, distance to urban or other grove occurrences proved to be among the most important variables. During the early phase of D. citri invasion in the region, groves closer to urban occurrences were invaded more rapidly, whereas more recently, invasion rate depended primarily on proximity to grove occurrences. Yet, proximity to urban and grove occurrences contributed positively to cumulative D. citri detections, suggesting a continued influx from both sources. These results suggest that inherent features of agroecosystems and spatial coupling with urban ecosystems can be important, temporally dynamic, drivers of biological invasions. Further consideration of these issues may guide the development of strategic responses to D. citri's ongoing invasion.

Impact of Urbanisation Intensity on Bird Diversity in River Wetlands around Chaohu Lake, China.

Simple SummaryThe continuous intensification of urbanisation has led to severe degradation and loss of bird habitats, directly affecting the diversity of birds. In this study, we focused on seven representative river wetlands around Chaohu Lake (China) to analyse the impact of urbanisation on bird diversity. The species richness at sections of the lake entrance was higher than in the middle sections of the river, and the Shannon–Wiener index during autumn was higher than that during winter. Urbanisation was an important driving factor that changed land use types near rivers and the structure of bird communities. The response model of river ecological indicators to the intensity of urbanisation shows a negative exponential correlation between the waterbird diversity index and the urbanisation intensity. Our research is of great significance for future urban landscape planning and bird community diversity protection.Urbanisation is known to result in ‘urban stream syndrome’, which poses a huge threat to the river health. Birds, which are an important part of the river ecosystem, are sensitive to environmental changes in the basin. The ratio of the impervious surface area is a macroscopic indicator of urbanisation intensity in river basins. In this study, we combined the results of a year-round field survey of seven river wetlands around Chaohu Lake (China) with satellite remote sensing image data from the same period. The species richness at sections of the lake entrance was higher than in the middle sections of the river, and the Shannon–Wiener index during autumn was higher than that during winter. The waterbird diversity index declined exponentially with increases in the intensity of urbanisation. The changes in the land use patterns around river wetlands associated with urbanisation resulted in the loss of food resources and habitats. Therefore, the intensity of urbanisation was an important driving factor that leads to changes in the bird community structure of river wetlands, so it had a significant impact on the diversity of river wetland birds in all four seasons combined with a variety of influencing factors. Our research could be a guide for urban landscape planning and bird diversity protection. For example, the results suggested that it is necessary to identify river wetlands as an important part of the urban ecosystem, reduced building area, increased vegetation coverage, and retained slope protection and river beach land.

Inconsistent Patterns of Soil Fauna Biodiversity and Soil Physicochemical Characteristic Along an Urbanization Gradient

Urbanization has induced substantial changes in soil physicochemical characteristic, which plays an important role in regulating soil fauna biodiversity in forests and grasslands. However, less is known about the urbanization effect on soil fauna biodiversity and how soil physicochemical changes mediate this effect. Along an urbanization gradient in the city of Guangzhou, we established four sites with different urbanization intensities, including an urban site, two suburban sites, and a rural site, and then studied their soil physicochemical characteristic and soil fauna biodiversity. The soil physicochemical characteristic dramatically changed along the urbanization gradient. In contrast, the soil fauna biodiversity exhibited a very different pattern. Soil fauna abundance was highest in the suburban sites. Moreover, there were significant changes of Pielou’s evenness and community structure in the suburban sites. Soil fauna biodiversity property in the urban site was similar to that in the rural site, except that the rural site was characterized by Enchytraeidae while the urban site was not characterized by any taxa. Our linear and canonical correspondence analysis models suggested that soil physicochemical characteristic only contributed a little to the variance of soil fauna abundance (19%), taxa number (27%), and community structure (12%). In contrast, soil physicochemical characteristic explained about half of the variance in Shannon’s diversity and Pielou’s evenness. However, with urbanization intensity increasing, soil physicochemical changes could both increase and decrease the diversity and evenness. Thus, our results revealed an inconsistent pattern between soil fauna biodiversity and soil physicochemical characteristic along an urbanization gradient. This study suggested that soil physicochemical change was less important as expected in regulating soil fauna biodiversity pattern under an urbanization context. To elucidate the effect of urbanization on soil fauna biodiversity, further studies should take other urbanization agents into account.

The effect of gender equality on the carbon intensity of well-being: panel data analysis for the MENA economies 1995-2018

PurposeThis paper aims to explore the ecological efficiency through assessing the relation of the “carbon intensity of well-being” (CIWB) to gender equality, gross domestic product (GDP)/capita, the urban intensity of the population, the age structure of the population, foreign direct investment as a percentage of GDP and manufacturing as a percentage of GDP.Design/methodology/approachCIWB equation is estimated for a panel of 18 MENA economies and Turkey over the period 1995–2018 using the two-way fixed effects Prais–Winsten regression with panel-corrected standard errors.FindingsThe elasticity coefficients obtained from the estimated models indicated mixed effects on CIWB. While the increase of female educational attainment, accompanied with an increase in the female labor force participation rate, reduce CIWB, the younger female population and the younger population, in general, increase CIWB. Furthermore, while increasing FDI inflows reduces CIWB, increasing the manufacturing share of GDP increases CIWB.Originality/valueThe pursuit of Sustainable Development Goals worldwide has moved the relevant literature on climate change mitigation and adaptation measures to a new level, where using the CIWB method is increasingly used to reflect carbon dioxide emissions per capita unit of expected lifespan. The present paper’s contribution to the literature is two-fold: one is computing and estimating the CIWB to examine ecological efficiency for the middle east and north africa (MENA) economies and Turkey over the period of study; and two is integrating and validating the beneficial impacts of integrating the gender equality dimension in the CIWB–climate change literature.

Effect of Urbanization on Presence, Abundance, and Coinfection of Bacteria and Protozoa in Ticks in the US Great Plains.

Urbanization alters components of natural ecosystems which can affect tick abundance and tick-borne disease prevalence. Likely due to these changes, tick-borne pathogen prevalence has increased in many U.S. urban areas. Despite the growing public health importance of tick-borne diseases, little is known about how they are influenced by urbanization in North America, especially in the central U.S. where several pathogens occur at or near their highest levels of incidence nationally. To determine whether urban development influences tick infection with bacteria and protozoa, we collected ticks at 16 parks across a gradient of urbanization intensity in Oklahoma City, Oklahoma, USA and tested them using a variety of PCR assays. Adult ticks tested positive for Rickettsia parkeri, R. amblyommatis, R. rhiphicephali, 'Candidatus R. andeanae', Ehrlichia chaffeensis, E. ewingii, Panola Mountain Ehrlichia, 'Borrelia lonestari', Theileria cervi, Babesia spp. Coco, and Cytauxzoon felis. These results indicate the presence of a high diversity of tick-borne bacteria and protozoa across an expanding urban area in the U.S. Great Plains. Although there appeared to be some risk of encountering tick-borne microorganisms across the entire urbanization gradient, E. chaffeensis, E. ewingii, and T. cervi-infected ticks and microbe diversity decreased with increasing urbanization intensity. We identified a low rate of coinfection between different microorganisms, with coinfected ticks mainly collected from sites in the least-urbanized areas. This study suggests the need for awareness of tick-borne disease risk throughout urban areas in the central U.S., and highlights a need for studies of tick host habitat use and movement in cities.

Heavy metals from heavy land use? Spatio-temporal patterns of urban runoff metal loads

Urban hydrology is characterized by increased runoff and various pollutant sources. We studied the spatio-temporal patterns of stormwater metal (Al, V, Cr, Mn, Fe, Cu, Zn, and Pb) concentrations and loads in five urbanized and one rural catchment in Southern Finland. The two-year continuous monitoring revealed a non-linear seasonal relationship between catchment urban intensity and metal export. For runoff, seasonal variation decreased with increasing imperviousness. The most urbanized catchments experienced greatest temporal variation in metal concentrations: the annual Cu and Zn loads in most of the studied urbanized catchments were up to 86 times higher compared to the rural site, whereas Fe loads in the urbanized catchments were only circa 29% of the rural load. Total metal levels were highest in the winter, whereas the winter peak of dissolved metal concentrations was less pronounced. The collection of catchment characteristics explained well the total metal concentrations, whereas for the dissolved concentrations the explanatory power was weaker. Our catchment-scale analysis revealed a mosaic of mainly diffuse pollutant sources and calls for catchment-scale management designs. As urban metal export occurred across seasons, solutions that operate also in cold conditions are needed.

Urbanization-induced environmental changes strongly affect wetland soil bacterial community composition and diversity

Soil microbial communities potentially serve as indicators for their responses to changes in various ecosystems at scales from a region to the globe. However, changes in wetland soil bacterial communities and how they are related to urbanization intensities remains poorly understood. Here, we collected 60 soil samples along urbanization intensity gradients from 20 wetlands. We measured a range of environmental factors and characterized bacterial communities structure using 16S ribosomal RNA (16S rRNA) gene amplicon sequencing that targeted the V4-V5 region. Our results revealed the dominant soil bacterial phyla included Proteobacteria (39.3%), Acidobacteria (21.4%) and Chloroflexi (12.3%) in the wetlands, and showed a significant divergence of composition in intensive urbanization area (UI_4) than other places. A critical ‘threshold’ exists in the soil bacterial diversity, demonstrating different patterns: a gradual increase in the areas of low-to-intermediate disturbances but a significant decrease in highly urbanized areas where metabolic functions were significantly strong. Additionally, soil pH, total phosphorus (TP), available phosphorus (AP) and ammonia nitrogen (NH4 +-N) made a significant contribution to variations in bacterial communities, explaining 49.6%, 35.1%, 26.2% and 30.7% of the total variance, respectively. pH and NH4 +-N were identified as the main environmental drivers to determine bacterial community structure and diversity in the urban wetlands. Our results highlight collective changes in multiple environmental variables induced by urbanization rather than by the proportion of impervious surface area (ISA), which were potentially attributed to the spatial heterogeneity along different urbanization gradients.

基于街景测量的南昌市行道树结构特征与健康状况研究

行道树作为城市绿地系统的网络和骨架, 在城市居民生活中发挥着无可替代的作用。快速准确的掌握城市行道树的结构特征和健康状况, 有利于城市森林建设与管理, 进而提升其生态服务功能。基于百度街景平台, 通过街景测树法对南昌市的963个样方, 共计26727株行道树展开调查。测量内容包括行道树大小指标(树高、胸径、冠下高和冠幅)、健康状况(支架比例、枯稍比例、叶色不健康比例和死亡比例)和植被垂直结构配置情况; 并且探究了不同行政区和不同城市化强度(环城道路发展下的城乡梯度)下行道树的空间分布特征。结果表明: (1)南昌市行道树小树比例较高: 胸径在10-20 cm的占65%, 冠下高在1.5-2.5 m间的占76%, 树高在4-8 m间的占71%, 冠幅在2-6 m间的占76%;行道树生长整体表现为健康, 各指标所占比例较小, 但是叶片健康较差; 35%的样地无叶色不健康, 77%的样地无支架, 76%的样地无枯梢, 93%的样地无死亡; 植被垂直结构配置状况良好, 以乔-灌-草复合结构为主(比重为75%); (2)在空间分布上, 不同行政区行道树大小指标和垂直结构配置上差异显著、健康状况(支架比例和叶色不健康比例)均表现显著性差异(P < 0.05);不同环路行道树大小指标存在显著差异, 表现为1环>2环>3环, 垂直结构从内环到外环更为复杂, 配置等级为1环 < 2环 < 3环, 不同环路行道树健康状况(支架比例和叶色不健康比例)表现显著性差异(P < 0.05)。综上所述, 南昌市行道树整体健康状况良好, 行道树个体较小, 而且以复层结构为主, 本研究基于百度街景对南昌市行道树结构特征和健康状况进行比较全面的评价, 为南昌市今后城市行道树的规划和管理提供了基础数据支持。;As the network and skeleton of urban green space system, roadside trees play an irreplaceable role in urban residents' life. Rapid and accurate grasp of the structural characteristics and health status of urban roadside trees is conducive to the construction and management of urban forest, thus improving its ecological service function. Based on the Baidu Street View platform, this study investigated 963 quadrats, a total of 26, 727 roadside trees, in Nanchang by street view tree measurement method. Measures included indicators of street tree sizes (diameter at breast height (DBH), underbranch height (UBH), tree height (TH) and canopy size (CS)), health status (the proportion of Tripod-supporting, the proportion of Dieback, the proportion of Non-greenness leaf color and the proportion of Death trees), and vertical structure configuration of vegetation. Moreover, the spatial distribution characteristics of road trees under different administrative regions and different urbanization intensities (urban and rural gradient under the development of ring roads) were explored. The results showed that: (1) there was a high proportion of small trees in Nanchang: DBH of 10─20 cm accounted for 65%, UBH of 1.5─2.5 m accounted for 76%, TH of 4─8 m accounted for 71%, CS of 2─6 m accounted for 76%. The overall performance of the growth of street trees was healthy, the proportion of each index was small, but the leaf health was poor. In 35% of the plots, no leaf color was unhealthy, 77% of the plots had no Tripod-supporting, 76% of the plots had no Dieback and 93% of the plots had no death. The vertical structure of vegetation was in good condition, mainly composed of arbor-shrub-herb (75% of the sample land). (2) In terms of spatial distribution, there are significant differences in the sizes index and vertical structure configuration of road trees in different administrative areas, and significant differences in health status (proportion of Tripod-supporting and proportion of Non-greenness leaf color) (P < 0.05). There were urban-rural differences in the size index of road trees in different ring-road areas, which are manifested as 1^st ring > 2^nd ring > 3^rd ring, the vertical structure of the outer ring is more complex, configuration grade is 1^st ring < 2^nd ring < 3^rd ring. There were significant differences in the health status of different ring-road (proportion of Tripod-supporting and proportion of Non-greenness leaf color) (P < 0.05). To sum up, the overall health status of the roadside trees in Nanchang is good, the individual of the roadside trees is small, and they are mainly composed of multiple layers. Based on the Baidu Street View, this study makes a relatively comprehensive evaluation of the structural characteristics and health status of the roadside trees in Nanchang, which provides basic data support for the planning and management of the urban roadside trees in Nanchang in the future.