The term urban heat island (UHI) describes a phenomenon where cities are on average warmer than the surrounding rural area. Trees and greenspaces are recognised for their strong potential to regulate ...urban air temperatures and combat the UHI. Empirical data is required in the UK to inform predictions on cooling by urban greenspaces and guide planning to maximise cooling of urban populations. We describe a 5-month study to measure the temperature profile of one of central London's large greenspaces and also in an adjacent street to determine the extent to which the greenspace reduced night-time UHI intensity. Statistical modelling displayed an exponential decay in the extent of cooling with increased distance from the greenspace. The extent of cooling ranged from an estimated 20m on some nights to 440m on other nights. The mean temperature reduction over these distances was 1.1°C in the summer months, with a maximum of 4°C cooling observed on some nights. Results suggest that calculation of London's UHI using Met Stations close to urban greenspace can underestimate ‘urban’ heat island intensity due to the cooling effect of the greenspace and values could be in the region of 45% higher. Our results lend support to claims that urban greenspace is an important component of UHI mitigation strategies. Lack of certainty over the variables that govern the extent of the greenspace cooling influence indicates that the multifaceted roles of trees and greenspaces in the UK's urban environment merit further consideration.
•Trees help regulate urban air temperatures and combat the urban heat island effect.•We describe cooling of London's heat island by one large greenspace over 5months•Cooling of up to 4°C over 440m distance from the park was observed on single nights.•The park cooled London when cooling was most needed, on warm still nights.
Urbanisation and a changing climate are leading to more frequent and severe flood, heat and air pollution episodes in Britain's cities. Interest in nature-based solutions to these urban problems is ...growing, with urban forests potentially able to provide a range of regulating ecosystem services such as stormwater attenuation, heat amelioration and air purification. The extent to which these benefits are realized is largely dependent on urban forest management objectives, the availability of funding, and the understanding of ecosystem service concepts within local governments, the primary delivery agents of urban forests.
This study aims to establish the extent to which British local authorities actively manage their urban forests for regulating ecosystem services, and identify which resources local authorities most need in order to enhance provision of ecosystem services by Britain's urban forests.
Interviews were carried out with staff responsible for tree management decisions in fifteen major local authorities from across Britain, selected on the basis of their urban nature and high population density. Local authorities have a reactive approach to urban forest management, driven by human health and safety concerns and complaints about tree disservices. There is relatively little focus on ensuring provision of regulating ecosystem services, despite awareness by tree officers of the key role that urban forests can play in alleviating chronic air pollution, flood risk and urban heat anomalies. However, this is expected to become a greater focus in future provided that existing constraints – lack of understanding of ecosystem services amongst key stakeholders, limited political support, funding constraints – can be overcome.
Our findings suggest that the adoption of a proactive urban forest strategy, underpinned by quantified and valued urban forest-based ecosystem services provision data, and innovative private sector funding mechanisms, can facilitate a change to a proactive, ecosystem services approach to urban forest management.
•British urban forests are managed reactively, in response to risks and complaints.•Tree officers are aware of urban forests’ delivery of regulating ecosystem services.•Limited funding and lack of political support are obstacles to a proactive approach.•Awareness raising via ecosystem service valuation and strategic planning is needed.•Research into a public-private urban forest funding model would be beneficial.
•We monitored cooling by eight London greenspaces, with areas from 0.2 to 12.1ha.•Very small greenspaces (with areas <0.5ha) did not offer substantial cooling.•Cooling distance increased linearly ...with area of greenspace, tree canopy and grass.•Cooling intensity increased non-linearly with the different green areas.•Widespread cooling of a city may come from greenspaces of 3–5ha, set 150m apart.
Urban greenspaces can provide a significant cooling service, which extends beyond the greenspace boundaries. Consequently, greenspaces are recognised for their ability to locally reduce the urban heat island, a phenomenon that has negative implications for the thermal comfort and health of urban citizens. However, the amount of cooling provided by a greenspace and the distance over which that cooling extends depend on factors such as greenspace size and characteristics. Based on data collected in and around eight London greenspaces, with areas ranging from 0.2 to 12.1ha, this work models the distance and magnitude of cooling provided by each greenspace and defines the relationships between cooling extent and the size of greenspace or the areas of tree canopy and grass. Such data, illustrating the value of expanding the area of urban greenspaces and explaining how cooling relates to greenspace size/coverage characteristics, will be of use to urban planners and climatologists concerned with finding solutions to the urban heat island. Modelling was statistically valid on calm warm nights (with mean air temperatures ≥10°C and wind speed ≤3ms−1). On those nights, cooling distance increased linearly with increasing area of greenspace, tree canopy and grass, but the relationship between those factors and the amount of cooling was non-linear. Cooling distance was most strongly related with tree canopy whereas the amount of cooling was most strongly linked to the grass coverage. Our results suggest that a comprehensive cooling service on calm warm nights within cities with similar climate/characteristics to London may come from greenspaces with 3–5ha, situated 100–150m apart.
There has been and continues to be considerable scientific interest in predicting bioremediation rates and endpoints. This requires the development of chemical techniques capable of reliably ...predicting the bioavailability of organic compounds to catabolically active soil microbes. A major issue in understanding the link between chemical extraction and bioavailability is the problem of definition; there are numerous definitions, of varying degrees of complexity and relevance, to the interaction between organic contaminants and microorganisms in soil. The aim of this review is to consider the bioavailability as a descriptor for the rate and extent of biodegradation and, in an applied sense, bioremediation of organic contaminants in soil. To address this, the review will (i) consider and clarify the numerous definitions of bioavailability and discuss the usefulness of the term ‘bioaccessibility’; (ii) relate definition to the microbiological and chemical measurement of organic contaminants' bioavailability in soil, and (iii) explore the mechanisms employed by soil microorganisms to attack organic contaminants in soil.
Understanding organic contaminant's behaviour in soil is key to chemically predicting biodegradation.
Semple, et al attempt to define the terms bioavailability and bioaccessiblity in order to stimulate further discussion about the terms and to promote understanding given the legal and regulatory ...implications of the concepts. The definitions are linked to processes described in a process report by the National Research Council called Bioavailability of Contaminants in Soils and Sediments: Processes, Tools, and Applications by Laura Ehlers and Richard Luthy.
Abstract
Urban trees are instrumental in providing ecosystem services to urban society. However, they are subject to many pressures linked to harsh site conditions created by the urban environment, ...climate change, attack by pests and diseases and the political and social influences that control how urban trees are perceived and managed. An ongoing provision of services from all trees within an urban area (known as the urban forest) can only be achieved through high resilience to these pressures. This study aims to examine the current state of composition, condition and structure of 12 urban forests across Great Britain, by reviewing data collected from i-Tree Eco city or town-wide surveys and recommending a framework to rate their sustainability. The study shows that urban forests are hardy to local winter temperatures and in good health, but lack in large size trees and tree species diversity. Also, several urban forests offer small percentage canopy cover. The wider application of this framework and the creation of detailed tree strategies could help local authorities to establish management strategies, set goals and monitor progress towards achieving greater sustainability.
•The fate and behaviour of contaminants in soil are key to their risk assessment and remediation.•No single chemical assay can determine the bioavailability/accessibility of contaminants in ...soil.•Determination of bioaccessibility will improve the risk assessment of contaminated land.
Risk assessment and remediation of contaminated land is inherently dependent on the contaminants present and their availability for interaction with soil biota. An ever-growing body of evidence suggests that current regulatory procedures over-estimate the ‘true’ fraction available to biota. Thus, a procedure that predicts the ‘bioavailable fraction’ would be useful for predicting ‘actual’ exposure limits and provide a more relevant basis for risk assessment. The aim of this paper is to address several important questions: “How should bioavailability be defined?” “What factors affect bioavailability measurement?” “To what extent have existing protocols measured bioavailability?” “What is actually measured by chemical techniques purported to determine bioavailability?” We offer two definitions (namely ‘bioavailability’ and ‘bioaccessibility’) and review commonly employed chemical extraction techniques to measure putative bioavailability. Relative advantages and disadvantages of the techniques are highlighted to elucidate underlying factors for the wide range of conclusions observed in the literature. Although the concept of bioavailability is implicit to contaminated land risk assessment and remediation, explicit reference to and use of adjustment factors is rare amongst regulatory bodies and remediators. Use of chemical determinants for bioavailability, applicable within current legislation and due consideration to inherent variability, are proposed and barriers to their implementation discussed.
Increasing urbanisation poses numerous challenges to human quality of life. Cities are particularly vulnerable to the urban heat-island effect, which will be amplified by climate change. Increasing ...tree cover may be one of the most cost-effective ways of moderating urban temperatures. Trees cool their surroundings by casting shade, reflecting solar radiation, transpiring, and intercepting rainfall that subsequently evaporates. However, the potential of trees to reduce the urban heat-island effect is underutilised. The aim of this study was to synthesise understanding of the relative abilities of different tree species to provide urban cooling in temperate regions of the world and thereby develop a pragmatic approach for choosing those trees that have greatest potential in that regard. Based on a literature review and semi-structured interviews with leading experts, we developed a series of scenarios to illustrate the impacts of a tree’s cooling mechanisms and tree species’ attributes on components of the surface-energy balance equation. This enabled us to select parameters and propose simple equations that can be used to compare the relative abilities of tree species in relation to each of the cooling mechanisms. The parameters selected were for: transpiration – crown diameter, Leaf Area Index (LAI), canopy aspect ratio, and stomatal conductance or growth rate; reflection – albedo, crown diameter and LAI; shading – canopy aspect ratio, crown diameter, LAI and tree height. The approach is intended for use by urban planners and managers who wish to make informed decisions about which tree species to select for planting to counter the urban heat-island effect.
Brownfield regeneration to soft reuse such as recreation and amenity has become increasingly common due to the demand for the potential environmental, social and economic benefits that it can ...deliver. This has led in turn to an increased demand for improved tools to support decision-making for this style of regeneration: tools which are simple to use, based on robust scientific principles and preferably which can ultimately link to quantitative or semi-quantitative cost-benefit analyses. This work presents an approach to assessing and comparing different scenarios for brownfield regeneration to soft reuse and other end-points. A “sustainability linkages” approach, based on sustainability assessment criteria produced by the UK Sustainable Remediation Forum (SuRF-UK), is developed and used in a refined qualitative sustainability assessment, and applied to develop a conceptual site model of sustainability, for a specific case study site (Port Sunlight River Park, U.K., a public leisure park established and maintained on a capped and managed former landfill site). Ranking, on an ex post basis, highlighted the clear sustainability advantages that the establishment of the Port Sunlight River Park has compared with a hypothetical non-development scenario. The conceptual site model provides a clearer basis for understanding cause and effect for benefits and disbenefits and a rationale for grouping individual effects based on their ease of valuation, providing a road map for cost-benefit assessments by (1) being able to match specific linkages to the most appropriate means of valuation, and (2) transparently connecting the sustainability assessment and cost benefit assessment processes.
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•SuRF-UK published a framework and indicators for sustainable remediation 2010/11.•The SuRF-UK approach was applied retrospectively to a landfill reuse project.•Qualitative assessment shows benefits in developing the park on the former landfill.•Sustainability linkages were used to develop a site specific sustainability model.•This conceptual site model facilitates both qualitative and quantitative valuation.
Tree allometric relationships were studied for seven species from eight GB cities.Relationships varied significantly between locations and species.Species curves can represent accurately mean ...relationships of young trees.Species curves over/underestimate mean relationships of mature trees by up to 30%.Crown width can be confidently predicted from DBH measurements.
Tree allometry describes the relationship between tree biometric variables, such as tree diameter (at breast height, DBH), height and crown width and helps urban foresters to assess many of the economic and ecological benefits provided by trees of different size. However, there is little knowledge on how the relationships established between those variables change between trees from different urban areas or species, especially within Great Britain (GB). This study aims to evaluate the variation in the allometric relationships of seven tree species growing in eight GB urban areas, and to understand if the use of generic curves representing relationships of trees growing across all locations is adequate. The variation between locations was highly significant; nevertheless, mean relationships of young trees growing in different locations were still accurately represented by a common species curve. Species with a similar stature also showed significant differences in their mean allometric relationships, reducing the level of accuracy when estimating mean relationships with multiple-species curves. Findings also suggest that crown width could be correctly predicted from DBH measurements. This knowledge can be used in citizen science based surveys, where the measurement of crown width is required but often challenging.
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