Assessing the ecosystem service of air pollutant removal by urban trees in Guangzhou (China)

In Chinese cities, air pollution has become a serious and aggravating environmental problem undermining the sustainability of urban ecosystems and the quality of urban life. Besides technical solutions to abate air pollution, urban vegetation is increasingly recognized as an alternative ameliorative method by removing some pollutants mainly through dry deposition process. This paper assesses the capability and monetary value of this ecosystem service in Guangzhou city in South China. The results indicated an annual removal of SO(2), NO(2) and total suspended particulates at about 312.03Mg, and the benefits were valued at RMB90.19 thousand (US$1.00=RMB8.26). More removal was realized by recreational land use due to a higher tree cover. Higher concentration of pollutants in the dry winter months induced more removal. The lower cost of pollution abatement in China generated a relatively subdued monetary value of this environmental benefit in comparison with developed countries. Younger districts with more extensive urban trees stripped more pollutants from the air, and this capacity was anticipated to increase further as their trees gradually reach final dimensions and establish a greater tree cover. Tree cover and pollutant concentration constitute the main factors in pollutant removal by urban trees. The efficiency of atmospheric cleansing by trees in congested Chinese cities could be improved by planting more trees other than shrubs or grass, diversifying species composition and biomass structure, and providing sound green space management. The implications for greenery design were discussed with a view to maximizing this ecosystem service in Chinese cities and other developing metropolises.     

Evaluation of Heritage Trees for Conservation and Management in Guangzhou City (China)

The recent fast pace of urbanization in China and other developing countries has exerted pressure on urban trees, which constitute a key urban environmental asset. The most outstanding trees should be treated as natural-cum-cultural heritage. Guangzhou Citys growth has threatened its rich urban-tree endowment, a diversified assemblage of 200,000 trees represented by 254 species and located in three major habitats: roadside, park, and institutional grounds. Mainly based on age and performance, 348 trees were officially designated as heritage specimens. They were evaluated in the field for tree dimensions, habitat, performance, and landscape contribution, to establish enhanced conservation and management strategies. With only 25 species, heritage trees were dominated by five cultivated natives and encompass some of the citys rare species; some common urban-forest species were not represented. Older districts and roadside habitats, despite their compact town plan and limited growing space, had the largest tree dimensions and largest share of heritage trees. Many heritage trees were large with long life expectancy and the potential for biomass expansion, and had pivotal cityscape impacts where they occur. Old neighborhoods, traditional haven for the arborescent treasure, are being changed by construction activities and periodic typhoon and windstorm damages. Increasing development density could degrade the heritage trees and their growing space, and reduce tree quality and life span. Upgrading the statutory-administrative systems and arboricultural care can enhance long-term survival of the precious natural-cum-cultural heritage. The experience of Guangzhou in identifying and preserving its high-quality urban trees can provide management strategies for other cities.     

Monitoring the performance and decline of heritage trees in urban Hong Kong

Urban trees in Hong Kong exist in stressful and harsh habitat conditions due mainly to the exceptionally high-density development mode. This study focuses on the cream of the urban tree stock, the heritage trees, which were selected according to five sets of stringent criteria: species, dimension, structure, condition, location, and special considerations. The study area covers the main urban core of the city. The loss of trees in two periods, 1993-1998 and 1999-2003, was monitored, with the predisposing and direct causes of damages ascertained as far as possible. Of the 380 heritage specimens, 54 trees were lost in the survey period. The main predisposing causes were injuries sustained in roadwork and construction activities, both related to root damage and soil disturbance. The principal direct causes were recent gradual decline and abrupt demise due to typhoon breakage. Three pairs of contributing variables registered statistically significant associations (chi(2) test), namely predisposing cause versus direct cause, tree growth form versus direct cause, and survey period versus direct cause. Principal component analysis identified three factors that explained 70% of the variance, namely tree form, tree stature, and growth environment. The main reasons for the high mortality were explored. The possible applications of the findings to improve tree protection and management were discussed in relation to the overall planning for meritorious greenery and green space especially in compact cities.     

Resilience to heat in public space: a case study of Adelaide,South Australia

During summer heatwaves, heat load exacerbates in urban heat islands (especially in hot climates) and threatens public life in cities. This paper examines the links between urban microclimates, outdoor thermal discomfort and public life through an exploratory case study. Heat resilience is highlighted as the ability of the space to support its normal activities when experiencing out-of-comfort temperatures. It also reports on the correlations between heat sensitive outdoor activities and urban greenery in three disparate case studies in Adelaide. Results indicate that necessary and optional activities start to decline after the apparent temperature reaches the threshold of 28?°C–32 °C, while activities in public spaces with more urban greenery show higher resilience to heat stress. Research findings propose heat resilience as a quality indicator in public space and support the application of urban greenery to make urban settings more resilient to heat stress.     

城市绿化规划研究初探--以长沙市雨花区为例

城市绿化规划是城市生态规划的基本内容。本文以长沙市雨花区为例，运用景观生态学原理，分析了城市绿地系统建设存在的问题，提出了城市生态绿地系统规划的基本内容和生态对策，可为一些城市的生态建设提供参考依据。     

Resource management as a key factor for sustainable urban planning

Due to fast urbanization and increasing living standards, the environmental sustainability of our global society becomes more and more questionable. In this historical review we investigate the role of resources management (RM) and urban planning (UP) and propose ways for integration in sustainable development (SD). RM follows the principle of circular causation, and we reflect on to what extent RM has been an element for urban planning. Since the existence of the first settlements, a close relationship between RM, urbanization and technological development has been present. RM followed the demand for urban resources like water, energy, and food. In history, RM has been fostered by innovation and technology developments and has driven population growth and urbanization. Recent massive resource demand, especially in relation to energy and material flows, has altered natural ecosystems and has resulted in environmental degradation. UP has developed separately in response to different questions. UP followed the demand for improved living conditions, often associated to safety, good manufacturing and trading conditions and appropriate sanitation and waste management. In history UP has been a developing research area, especially since the industrial era and the related strong urbanization at the end of the 18th century. UP responded to new emerging problems in urban areas and became increasingly complex. Nowadays, UP has to address many objectives that are often conflicting, including, the urban sustainability. Our current urban un-sustainability is rooted in massive resource consumption and waste production beyond natural limits, and the absence of flows from waste to resources. Therefore, sustainable urban development requires integration of RM into UP. We propose new ways to this integration.     

Analyzing the cost effectiveness of Santiago, Chile's policy of using urban forests to improve air quality

Santiago, Chile has the distinction of having among the worst urban air pollution problems in Latin America. As part of an atmospheric pollution reduction plan, the Santiago Regional Metropolitan government defined an environmental policy goal of using urban forests to remove particulate matter less than 10 microm (PM(10)) in the Gran Santiago area. We used cost effectiveness, or the process of establishing costs and selecting least cost alternatives for obtaining a defined policy goal of PM(10) removal, to analyze this policy goal. For this study, we quantified PM(10) removal by Santiago's urban forests based on socioeconomic strata and using field and real-time pollution and climate data via a dry deposition urban forest effects model. Municipal urban forest management costs were estimated using management cost surveys and Chilean Ministry of Planning and Cooperation documents. Results indicate that managing municipal urban forests (trees, shrubs, and grass whose management is under the jurisdiction of Santiago's 36 municipalities) to remove PM(10) was a cost-effective policy for abating PM(10) based on criteria set by the World Bank. In addition, we compared the cost effectiveness of managing municipal urban forests and street trees to other control policies (e.g. alternative fuels) to abate PM(10) in Santiago and determined that municipal urban forest management efficiency was similar to these other air quality improvement measures.     

Can urban tree roots improve infiltration through compacted subsoils for stormwater management?

Global land use patterns and increasing pressures on water resources demand creative urban stormwater management. Strategies encouraging infiltration can enhance groundwater recharge and water quality. Urban subsoils are often relatively impermeable, and the construction of many stormwater detention best management practices (D-BMPs) exacerbates this condition. Root paths can act as conduits for water, but this function has not been demonstrated for stormwater BMPs where standing water and dense subsoils create a unique environment. We examined whether tree roots can penetrate compacted subsoils and increase infiltration rates in the context of a novel infiltration BMP (I-BMP). Black oak (Quercus velutina Lam.) and red maple (Acer rubrum L.) trees, and an unplanted control, were installed in cylindrical planting sleeves surrounded by clay loam soil at two compaction levels (bulk density = 1.3 or 1.6 g cm(-3)) in irrigated containers. Roots of both species penetrated the more compacted soil, increasing infiltration rates by an average of 153%. Similarly, green ash (Fraxinus pennsylvanica Marsh.) trees were grown in CUSoil (Amereq Corp., New York) separated from compacted clay loam subsoil (1.6 g cm(-3)) by a geotextile. A drain hole at mid depth in the CUSoil layer mimicked the overflow drain in a stormwater I-BMP thus allowing water to pool above the subsoil. Roots penetrated the geotextile and subsoil and increased average infiltration rate 27-fold compared to unplanted controls. Although high water tables may limit tree rooting depth, some species may be effective tools for increasing water infiltration and enhancing groundwater recharge in this and other I-BMPs (e.g., raingardens and bioswales).     

Effects of Increasing Urbanization on the Ecological Integrity of Open Space Preserves

This article analyzes the effects of increasing urbanization on open space preserves within the metropolitan area of Phoenix, Arizona, USA. Time series analysis is used in 10-year increments over 40 years to study urban landscape change. Three landscape metrics—(1) matrix utility (measures intensity of adjacent land uses), (2) isolation (measures distances to other open space patches), and (3) connectivity (measures physical links to other open space patches and corridors)—are used to assess changes in landscape patterns and serve as indicators of urban ecological integrity of the open space preserves. Results show that in the case of both open space preserves, general decline in indicators of urban ecological integrity was evident. The matrix utility analysis demonstrated that increasing intensity of land uses adjacent to preserve is likely to increase edge effects, reducing the habitat value of interior or core habitat areas. Isolation analysis showed that both preserves have experienced increasing isolation from other open space elements over time. Also, connectivity analysis indicated that terrestrial connections to other open space elements have also deteriorated. Conclusions of this research demonstrate that while preservation of natural areas as open space is important in an urban context, intense development of surrounding areas reduces the urban ecological integrity significantly.     

Structure of a forested urban park: Implications for strategic management

Informed management of urban parks can provide optimal conditions for tree establishment and growth and thus maximize the ecological and aesthetic benefits that trees provide. This study assesses the structure, and its implications for function, of the urban forest in Allan Gardens, a 6.1 ha downtown park in the City of Toronto, Canada, using the Street Tree Resource Analysis Tool for Urban Forest Managers (STRATUM). Our goal is to present a framework for collection and analysis of baseline data that can inform a management strategy that would serve to protect and enhance this significant natural asset. We found that Allan Garden’s tree population, while species rich (43), is dominated by maple (Acer spp.) (48% of all park trees), making it reliant on very few species for the majority of its ecological and aesthetic benefits and raising disease and pest-related concerns. Age profiles (using size as a proxy) showed a dominance of older trees with an inadequate number of individuals in the young to early middle age cohort necessary for short- to medium-term replacement. Because leaf area represents the single-most important contributor to urban tree benefits modelling, we calculated it separately for every park tree, using hemispheric photography, to document current canopy condition. These empirical measurements were lower than estimates produced by STRATUM, especially when trees were in decline and lacked full canopies, highlighting the importance of individual tree condition in determining leaf area and hence overall forest benefits. Stewardship of natural spaces within cities demands access to accurate and timely resource-specific data. Our work provides an uncomplicated approach to the acquisition and interpretation of these data in the context of a forested urban park.     

Nest-Site Selection by Black Sparrowhawks Accipiter melanoleucus: Implications for Managing Exotic Pulpwood and Sawlog Forests in South Africa

This study provides timber growers with silvicultural guidelines for establishing and maintaining nest-tree habitat for native black sparrowhawks (Accipiter melanoleucus) in commercial planted forests in South Africa. In this country, exotic eucalypts and pines are planted principally for pulpwood and sawlog production. Nineteen nests were sampled in indigenous forests and 58 nests in exotic forests. Although mean nest heights differed between indigenous and exotic trees, in all trees, nests were positioned, on average, at 64% of tree height. Black sparrowhawks nested near stand edges, probably seeking a compromise between nesting adjacent to open hunting habitat and selecting an insulated tree from within the forest. Black sparrowhawks nested in tall trees ( X- = 18-33 m for different tree species classes) with a large diameter (>60 cm). Unfortunately, the South African pulpwood and sawlog industry employ short rotations (<16 years) and high tree densities (>700 trees/ha) that do not allow the trees to attain the characteristics suitable for black sparrowhawk nesting sites. Eucalypt and pine nest stands must be of 25 x 25 m minimum size and incorporate 10 trees at minimum heights of 21 and 18 m and diameters of 37 and 35 cm, respectively. If such nest-tree stands are set aside as islands in a sea of commercial forests, and black sparrowhawks and other forest raptors nest in them, timber growers will improve the tree-nesting raptor diversity of planted forests. If, however, these raptors prey upon species of conservation importance, the management recommendations could be reversed to limit the potential for predation.     

A Management-Orientated Comparative Analysis of Urban and Rural Anglers Living in a Metropolis (Berlin,Germany)

Increased efforts to analyze the human dimensions of anglers are necessary to improve freshwater fisheries management. This paper is a comparative analysis of urban and rural anglers living in a metropolis, based on n = 1061 anglers responding to a mail survey in the German capital of Berlin. More than two thirds of the anglers (71%) had spent most (>50%) of their effort outside the city borders of Berlin and thus were categorized as rural anglers. Compared to the rural anglers, urban anglers (50% of total effort spent inside the city) were younger and less educated. Urban anglers were more avid and committed, less mobile, and more frequently fished from boats and during weekdays. Rural anglers were more experienced, fished for longer times per trip, fished more often at weekends and on holidays, were more often members of angling clubs, and more frequently caught higher valued fish species. The achievement and fish quantity aspects of the angling experience were more important for urban than for rural anglers. Concerning management options, urban anglers more frequently suggested constraining other stakeholders and reducing regulations, whereas rural anglers more often proposed improving physical access to angling sites. Future urban fishing programs should offer ease of access, connection to public transportation, moderate prices, and diverse piscivorous fish stocks. In contrast to rural fisheries, the provision of high ecological and aesthetical quality of the angling waters can be regarded as of minor importance in urban fisheries. Rural fisheries managers need to consider the needs of stakeholders living in Berlin to minimize impacts on the less degraded rural water bodies and potential user conflicts with resident anglers. Ecosystem-based management approaches should guide rural fisheries policy.     

Urban channel adjustments in a management context: an Australian example

The impact of urbanization on stream channels has been investigated in a range of areas; the degree and extent of the channel adjustments have been demonstrated; and for a few areas these characteristics have recently been placed into a spatial context. A method of rapid field survey for depicting the channel network of urban areas in terms of near natural, adjusted, and channelized systems is illustrated for the urban area of Armidale NSW, for which Armidale Dumaresq Council had prepared a stormwater management plan. Such a survey could enable channel characteristics and adjustments, as well as water quantity and quality, to be included in the management plan. Possible options for management to address are suggested for each of the channel categories. A channel classification system of the kind suggested can provide a basic complement for the further development of the stormwater management plan, can afford a basis for specifying management alternatives, and can be helpful in demonstrating the options offered for community consultation.     

Mechanistic Simulation of Tree Effects in an Urban Water Balance Model1

Abstract: A semidistributed, physical‐based Urban Forest Effects – Hydrology (UFORE‐Hydro) model was created to simulate and study tree effects on urban hydrology and guide management of urban runoff at the catchment scale. The model simulates hydrological processes of precipitation, interception, evaporation, infiltration, and runoff using data inputs of weather, elevation, and land cover along with nine channel, soil, and vegetation parameters. Weather data are pre‐processed by UFORE using Penman‐Monteith equations to provide potential evaporation terms for open water and vegetation. Canopy interception algorithms modified established routines to better account for variable density urban trees, short vegetation, and seasonal growth phenology. Actual evaporation algorithms allocate potential energy between leaf surface storage and transpiration from soil storage. Infiltration algorithms use a variable rain rate Green‐Ampt formulation and handle both infiltration excess and saturation excess ponding and runoff. Stream discharge is the sum of surface runoff and TOPMODEL‐based subsurface flow equations. Automated calibration routines that use observed discharge has been coupled to the model. Once calibrated, the model can examine how alternative tree management schemes impact urban runoff. UFORE‐Hydro model testing in the urban Dead Run catchment of Baltimore, Maryland, illustrated how trees significantly reduce runoff for low intensity and short duration precipitation events.     

How “open” are open spaces: evaluating transformation of open space at residential level in Adelaide – a case study

This paper examines the transformation of open space and how it compares to older residential development. A study has been conducted at the residential level because neighbourhoods have been a basic unit of city design throughout the recent history of urban settlements. Furthermore, the neighbourhood is a more humanly relevant scale of urban development. The method adopted for this research was a comparative urbanism by comparing old and new residential areas. This study found that incremental redevelopment of old residential areas through both re-subdivision and intensification of development on existing allotments has resulted in a progressive loss of open space. However, the study also confirmed that the current supplies of open space across all the study areas (old and new residential areas) are relatively similar. The main difference between the open space supply in older and newer residential areas comes down to the ownership of land (i.e. the proportion of public versus private open space). The study demonstrated that older residential areas with large allotments have experienced a significant loss of private open space – originally from 50%, to current levels of 23–30%. The paper concludes that there is a need for a holistic approach to the provision of public and private open spaces to improve the quality of life at a residential level.     

Identification and quantification of the hydrological impacts of imperviousness in urban catchments: a review

Urbanisation produces numerous changes in the natural environments it replaces. The impacts include habitat fragmentation and changes to both the quality and quantity of the stormwater runoff, and result in changes to hydrological systems. This review integrates research in relatively diverse areas to examine how the impacts of urban imperviousness on hydrological systems can be quantified and modelled. It examines the nature of reported impacts of urbanisation on hydrological systems over four decades, including the effects of changes in imperviousness within catchments, and some inconsistencies in studies of the impacts of urbanisation. The distribution of imperviousness within urban areas is important in understanding the impacts of urbanisation and quantification requires detailed characterisation of urban areas. As a result most mapping of urban areas uses remote sensing techniques and this review examines a range of techniques using medium and high resolution imagery, including spectral unmixing. The third section examines the ways in which scientists and hydrological and environmental engineers model and quantify water flows in urban areas, the nature of hydrological models and methods for their calibration. The final section examines additional factors which influence the impact of impervious surfaces and some uncertainties that exist in current knowledge.     

Rehabilitation and Flood Management Planning in a Steep,Boulder-Bedded Stream

This study demonstrates the integration of rehabilitation and flood management planning in a steep, boulder-bedded stream in a coastal urban catchment on the South Island of New Zealand. The Water of Leith, the primary stream flowing through the city of Dunedin, is used as a case study. The catchment is steep, with a short time of concentration and rapid hydrologic response, and the lower stream reaches are highly channelized with floodplain encroachment, a high potential for debris flows, significant flood risks, and severely degraded aquatic habitat. Because the objectives for rehabilitation and flood management in urban catchments are often conflicting, a number of types of analyses at both the catchment and the reach scales and careful planning with stakeholder consultation were needed for successful rehabilitation efforts. This included modeling and analysis of catchment hydrology, fluvial geomorphologic assessment, analysis of water quality and aquatic ecology, hydraulic modeling and flood risk evaluation, detailed feasibility studies, and preliminary design to optimize multiple rehabilitation and flood management objectives. The study showed that all of these analyses were needed for integrated rehabilitation and flood management and that some incremental improvements in stream ecological health, aesthetics, and public recreational opportunities could be achieved in this challenging environment. These methods should be considered in a range of types of stream rehabilitation projects.     

Impact of Urban Sprawl on Water Quality in Eastern Massachusetts,USA

A study of water quality, land use, and population variations over the past three decades was conducted in eastern Massachusetts to examine the impact of urban sprawl on water quality using geographic information system and statistical analyses. Since 1970, eastern Massachusetts has experienced pronounced urban sprawl, which has a substantial impact on water quality. High spatial correlations are found between water quality indicators (especially specific conductance, dissolved ions, including Ca, Mg, Na, and Cl, and dissolved solid) and urban sprawl indicators. Urbanized watersheds with high population density, high percentage of developed land use, and low per capita developed land use tended to have high concentrations of water pollutants. The impact of urban sprawl also shows clear spatial difference between suburban areas and central cities: The central cities experienced lower increases over time in specific conductance concentration, compared to suburban and rural areas. The impact of urban sprawl on water quality is attributed to the combined effects of population and land-use change. Per capita developed land use is a very important indicator for studying the impact of urban sprawl and improving land use and watershed management, because inclusion of this indicator can better explain the temporal and spatial variations of more water quality parameters than using individual land use or/and population density.     

An Application and Evaluation of the CAL3QHC Model for Predicting Carbon Monoxide Concentrations from Motor Vehicles Near a Roadway Intersection in Muscat,Oman

The CAL3QHC model was used to predict carbon monoxide (CO) concentrations from motor vehicles at an existing urban intersection (Star Cinema in Muscat area, Oman). The CO concentrations predicted from the model were compared with those measured in the field. Predicted average CO concentrations were found to compare favorably with measured values obtained at all eight receptors considered within the modeled intersection. In general, the comparison indicates good agreement with some underprediction for CO. For receptor 6, the model overpredicts the average CO concentration. This overprediction is associated with the presence of trees and green area in the location of receptor 6. In general, the measurements and the model results indicated that the highest CO concentrations were found to occur close to the intersection and, hence, a decrease in the concentration levels was seen as the distance from the road increased. The results indicated that the levels of CO were well below the ambient air quality standard and that probably no health risk was present in areas adjacent to the star cinema intersection. However, the predicted worst-case 1-h CO concentrations assuming inversion atmospheric stability conditions (class F) and wind speed of 1 m/s indicated that the levels of CO were close to or higher than the Omans National Ambient Air Quality Standards (NAAQS) value of 35 ppm at all receptors considered. The results of this study are useful in transport development and traffic management planning.Published online.     

An approach to tree thinning to structure southern African savannas for long-term restoration from bush encroachment

Due to bush encroachment the grazing capacity of large areas of the southern African savanna has declined, often to such an extent that many previously economic livestock properties are now no longer economically viable. Attempts at restoring encroached areas by the removal of some or all of the woody plants will normally result in an increase of grass production and thus also the grazing capacity. However, the results of woody plant removal may differ between vegetation types, with the outcome determined by both negative and positive responses to tree removal. The rapid establishment of tree seedlings after the removal of some or all of the mature woody plants may reduce the effective time span of restoration measures. In many cases the resultant re-establishment of new woody seedlings may in time develop into a state that is worse than the original state. This paper is an attempt to summarize existing knowledge on the importance of woody plants in savanna and explore measures, based on ecosystem dynamics, which can be utilized to restore encroached areas more successfully. It is hypothesized that a more stable environment can be created by maintaining or restoring savanna structure (large trees). In a structured savanna, large trees are able to suppress the establishment of new seedlings, while maintaining the other benefits of woody plants like soil enrichment and the provision of food to browsing herbivore species. Effective restoration of encroached areas should not be considered a once-off event, but rather a long-term commitment.