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Achieving urban sustainability goals, and improving the quality of life in cities, are aided by the careful selection of tree species for public green spaces. Numerous trade-offs and synergies are necessary to consider when selecting tree species for successful public green spaces. In this transdisciplinary research we consider the impacts of nine different tree planting scenarios, as modelled with i-Trees, in three piazzas of Bolzano, North Italy. The scenarios consider the opinions of the general public gathered from focused workshops and data collected via a purposefully created smartphone application. Shade provision and aesthetics were the primary factors that influenced citizen tree preferences. Scenarios which included larger tree species generally performed the best due to the greater provision of ecosystem services that arises with larger tree dimensions. Ecosystem disservices also increase with larger trees but can be minimised by careful species selection. Public participation in the planning of urban green spaces can be a beneficial activity which ensures new planning outputs will be well-received whilst providing opportunities for education of citizens about the multiple ecosystem services and disservices in urban contexts.
Andrew Speak; Leonardo Montagnani; Hilary Solly; Camilla Wellstein; Stefan Zerbe. The Impact of Different Tree Planting Strategies in the Piazzas of a Northern Italian City. 2021, 1 .
AMA StyleAndrew Speak, Leonardo Montagnani, Hilary Solly, Camilla Wellstein, Stefan Zerbe. The Impact of Different Tree Planting Strategies in the Piazzas of a Northern Italian City. . 2021; ():1.
Chicago/Turabian StyleAndrew Speak; Leonardo Montagnani; Hilary Solly; Camilla Wellstein; Stefan Zerbe. 2021. "The Impact of Different Tree Planting Strategies in the Piazzas of a Northern Italian City." , no. : 1.
Climate action plans, with goals for carbon neutrality of cities, often rely on estimates of urban forest biomass and related annual carbon sequestration balanced against citywide carbon emissions. For these estimates to be successful, there is a need both for accurate quantification of urban tree populations and structure, and consideration of the net carbon sequestered when the fate of wood waste is factored in. This study provides a novel approach to providing a full city tree inventory for the city of Meran in northern Italy, using a combination of Light Detection and Ranging (LiDAR) and field techniques. Allometric equations, and the i-Tree application quantified the carbon storage in Meran as 8923 and 9213 Mg respectively, with an average carbon storage of 13.5 t/ha (5.47 kg C/m2). The percentage of traffic emissions sequestered annually is 0.61% falling to 0.17% when all emissions are considered. Differences between end-of-life wood management techniques were revealed, with burning with energy recovery for electricity being the most efficient with a carbon emissions/input ratio of 0.5. Landfill was the least efficient with a ratio of 121.9. The fate of this end-of-life wood has significant implications for carbon budget calculations in cities worldwide.
Andrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. Total urban tree carbon storage and waste management emissions estimated using a combination of LiDAR, field measurements and an end-of-life wood approach. Journal of Cleaner Production 2020, 256, 120420 .
AMA StyleAndrew Speak, Francisco J. Escobedo, Alessio Russo, Stefan Zerbe. Total urban tree carbon storage and waste management emissions estimated using a combination of LiDAR, field measurements and an end-of-life wood approach. Journal of Cleaner Production. 2020; 256 ():120420.
Chicago/Turabian StyleAndrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. 2020. "Total urban tree carbon storage and waste management emissions estimated using a combination of LiDAR, field measurements and an end-of-life wood approach." Journal of Cleaner Production 256, no. : 120420.
The physical nature of the built urban environment gives rise to urban heat islands (UHI), making many cities frequently thermally uncomfortable in the summer, with potentially serious effects on human health. When climate change effects of higher summer temperatures and prolonged heatwaves are factored in, it is clear that adaptive measures are needed to ensure the liveability of cities. The shade provided by planting trees is one such adaptation measure. This study, in Bolzano, Italy, used a thermal camera to record the surface temperatures of three common urban surfaces – asphalt, porphyry, and grass – in the shade of 332 single tree crowns, of 85 different species, during the peak temperature period of summer days. By comparing with the temperature of adjacent unshaded ground, estimates of the degree of surface cooling were made. Measurements at three locations within the shadow revealed higher cooling in the centre and at the western edge. The cooling was related to a multitude of tree traits, of which Leaf Area Index estimate (LAIcept) and crown width were the most important. Median average cooling of 16.4, 12.9 and 8.5 °C was seen in the western edge of the tree shade for asphalt, porphyry and grass, respectively. Maximum temperatures were reduced by roughly 19 °C for all surface types. Coniferous trees were capable of providing high cooling, however, crown dimensions may limit the receiving surface area. Descriptive and predictive multiple linear regression models were able to predict cooling with some success from several of the predictor variables (LAIcept and gap fraction). Strategic planting of single trees in cities can have significant impacts on the absorption of solar radiation by ground surface materials thus reducing the heat storage that contributes to UHIs.
Andrew Speak; Leonardo Montagnani; Camilla Wellstein; Stefan Zerbe. The influence of tree traits on urban ground surface shade cooling. Landscape and Urban Planning 2020, 197, 103748 .
AMA StyleAndrew Speak, Leonardo Montagnani, Camilla Wellstein, Stefan Zerbe. The influence of tree traits on urban ground surface shade cooling. Landscape and Urban Planning. 2020; 197 ():103748.
Chicago/Turabian StyleAndrew Speak; Leonardo Montagnani; Camilla Wellstein; Stefan Zerbe. 2020. "The influence of tree traits on urban ground surface shade cooling." Landscape and Urban Planning 197, no. : 103748.
BackgroundThe glaciers in the Alps, as in other high mountain ranges and boreal zones, are generally retreating and leaving a wide surface of bare ground free from ice cover. This early stage soil is then colonized by microbes and vegetation in a process of primary succession. It is rarely experimentally examined whether this colonization process is linear or not at the ecosystem scale. Thus, to improve our understanding of the variables involved in the carbon accumulation in the different stages of primary succession, we conducted this research in three transects on the Matsch glacier forefield (Alps, N Italy) at an altitude between 2,350 and 2,800 m a.s.l.MethodsIn three field campaigns (July, August and September 2014) a closed transparent chamber was used to quantify the net ecosystem exchange (NEE) between the natural vegetation and the atmosphere. On the five plots established in each of the three transects, shading nets were used to determine ecosystem response function to variable light conditions. Ecosystem respiration (Reco) and gross ecosystem exchange (GEE) was partitioned from NEE. Following the final flux measurements, biometric sampling was conducted to establish soil carbon (C) and nitrogen (N) content and the biomass components for each transect.ResultsA clear difference was found between the earlier and the later successional stage. The older successional stages in the lower altitudes acted as a stronger C sink, where NEE, GEE and Reco were significantly higher than in the earlier successional stage. Of the two lower transects, the sink capacity of intermediate-succession plots exceeded that of the plots of older formation, in spite of the more developed soil. Total biomass (above- and belowground) approached its maximum value in the intermediate ecosystem, whilst the later stage of succession predominated in the corresponding belowground organic mass (biomass, N and C).OutlookWe found that the process of carbon accumulation along a glacier retreat chronosequence is not linear, and after a quite rapid increase in carbon accumulation capacity in the first 150 years, in average 9 g C m−2year−1, it slows down, taking place mainly in the belowground biomass components. Concurrently, the photosynthetic capacity peaks in the intermediate stage of ecosystem development. If confirmed by further studies on a larger scale, this study would provide evidence for a predominant effect of plant physiology over soil physical characteristics in the green-up phase after glacier retreat, which has to be taken into account in the creation of scenarios related to climate change and future land use.
Leonardo Montagnani; Aysan Badraghi; Andrew Speak; Camilla Wellstein; Luigimaria Borruso; Stefan Zerbe; Damiano Zanotelli. Evidence for a non-linear carbon accumulation pattern along an Alpine glacier retreat chronosequence in Northern Italy. PeerJ 2019, 7, e7703 .
AMA StyleLeonardo Montagnani, Aysan Badraghi, Andrew Speak, Camilla Wellstein, Luigimaria Borruso, Stefan Zerbe, Damiano Zanotelli. Evidence for a non-linear carbon accumulation pattern along an Alpine glacier retreat chronosequence in Northern Italy. PeerJ. 2019; 7 ():e7703.
Chicago/Turabian StyleLeonardo Montagnani; Aysan Badraghi; Andrew Speak; Camilla Wellstein; Luigimaria Borruso; Stefan Zerbe; Damiano Zanotelli. 2019. "Evidence for a non-linear carbon accumulation pattern along an Alpine glacier retreat chronosequence in Northern Italy." PeerJ 7, no. : e7703.
Considering ecosystem disservices (EDS) of urban forests alongside the services (ES) can lead to better-informed decisions about tree species selection and placement in cities. Finding a common assessment framework, that does not rely on a financial model, can be tricky, and many studies consider, but do not include, EDS in their tree appraisals. Compound indicators represent a means to neatly combine disparate ecosystem data into one meaningful metric. In this study quantitative field measurements, model outputs, and categorical data relating to some of the major ES and EDS of the urban forest of Meran, Italy, were successfully compressed into a single unit, overcoming epistemological boundaries surrounding different urban ecosystem valuation methods. Several methods of compound indicator construction were considered and uncertainty and sensitivity analysis carried out on the species rankings which were produced. Significant differences in ES/EDS provision were observed between trees on public and private land. Spatial analysis revealed hotspots of high ES provision and low EDS provision, and vice versa. With correct use, compound indicators can stand alongside other methods of measuring and valuing positive and negative aspects of urban ecosystems.
Andrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. An ecosystem service-disservice ratio: Using composite indicators to assess the net benefits of urban trees. Ecological Indicators 2018, 95, 544 -553.
AMA StyleAndrew Speak, Francisco J. Escobedo, Alessio Russo, Stefan Zerbe. An ecosystem service-disservice ratio: Using composite indicators to assess the net benefits of urban trees. Ecological Indicators. 2018; 95 ():544-553.
Chicago/Turabian StyleAndrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. 2018. "An ecosystem service-disservice ratio: Using composite indicators to assess the net benefits of urban trees." Ecological Indicators 95, no. : 544-553.
1. Urban forest ecosystems confer multiple ecosystem services. There is therefore a need to quantify ecological characteristics in terms of community structure and composition so that benefits can be better understood in ecosystem service models. Efficient sampling and monitoring methods are crucial in this process. 2 Full tree inventories are scarce due to time and financial constraints, thus a variety of sampling methods exist. Modern vegetation surveys increasingly use stratified‐random plot‐based sampling to reduce the bias associated with convenience sampling, even though the latter can save time and increase species richness scores. The urban landscape, with a high degree of conspecific clustering and high species diversity, provides a unique biogeographical case for comparing these two methodological approaches. 3 We use two spatially extensive convenience samples of the urban forest of Meran (Italy) and compare the community structure, tree characteristics and ecosystem service provision with 200 random circular plots. 4 The convenience sampling resulted in a higher species diversity, incorporating more rare species. This is a result of covering more area‐per‐unit sampling time. Pseudorandom sub‐plots were compared to the random plots revealing similar Shannon diversity and sampling comparability indices. Measured tree variables (diameter at breast height, height, tree‐crown width, height to crown base) were similar between the two methods, as were ecosystem service model outputs. 5 Synthesis and applications. Our results suggest that convenience sampling may be a time and money saving alternative to random sampling as long as stratification by land‐use type is incorporated into the design. The higher species richness can potentially improve the accuracy of urban ecological models, which rely on species‐specific functional traits. This article is protected by copyright. All rights reserved.
Andrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. Comparing convenience and probability sampling for urban ecology applications. Journal of Applied Ecology 2018, 55, 2332 -2342.
AMA StyleAndrew Speak, Francisco J. Escobedo, Alessio Russo, Stefan Zerbe. Comparing convenience and probability sampling for urban ecology applications. Journal of Applied Ecology. 2018; 55 (5):2332-2342.
Chicago/Turabian StyleAndrew Speak; Francisco J. Escobedo; Alessio Russo; Stefan Zerbe. 2018. "Comparing convenience and probability sampling for urban ecology applications." Journal of Applied Ecology 55, no. 5: 2332-2342.
Andrew Speak; A. Mizgajski; J. Borysiak. The spontaneous floral diversity of allotment gardens. Acta Horticulturae 2017, 389 -394.
AMA StyleAndrew Speak, A. Mizgajski, J. Borysiak. The spontaneous floral diversity of allotment gardens. Acta Horticulturae. 2017; (1189):389-394.
Chicago/Turabian StyleAndrew Speak; A. Mizgajski; J. Borysiak. 2017. "The spontaneous floral diversity of allotment gardens." Acta Horticulturae , no. 1189: 389-394.
Allotment gardens are a key feature of the urban landscape, providing numerous benefits beyond those of food production. These include ecosystem services such as local climate modification, pollination, and providing a pleasant location for socialising. The biodiversity of flora underpins many of these ecosystem services. The aims of this study are to assess the spontaneous vascular flora of urban allotment gardens and derive estimates of the species richness and diversity. In doing so, the specific position of allotment gardens within urban green infrastructure will be revealed and the role of allotment users in shaping local biodiversity determined. 358 species of spontaneous flora were recorded in 11 representative allotment garden estates (total area 150 ha) in Poznań, Poland. Fourteen biodiversity features were taken into account. The investigated areas exhibited high plant species richness, high diversity, low synanthropisation level, and contained valuable geobotanical elements, including plants of key importance for the European Community. For these reasons, allotment gardens should be considered as biodiversity hotspots for native species within urban green infrastructure. Based on an analysis of the spatial and functional organization of 110 individual plots, four types of usage, and corresponding plant diversity have been distinguished. The composition of the flora depends mostly on spatial and functional organization of allotment gardens and, to a much lesser extent, on the habitat conditions, which on individual plots varied very little. The high species richness and diversity in allotment gardens has important consequences for urban planning.
Janina Borysiak; Andrzej Mizgajski; Andrew Speak. Floral biodiversity of allotment gardens and its contribution to urban green infrastructure. Urban Ecosystems 2016, 20, 323 -335.
AMA StyleJanina Borysiak, Andrzej Mizgajski, Andrew Speak. Floral biodiversity of allotment gardens and its contribution to urban green infrastructure. Urban Ecosystems. 2016; 20 (2):323-335.
Chicago/Turabian StyleJanina Borysiak; Andrzej Mizgajski; Andrew Speak. 2016. "Floral biodiversity of allotment gardens and its contribution to urban green infrastructure." Urban Ecosystems 20, no. 2: 323-335.
D Polya; A Bualy; Andrew Speak; P Lythgoe; A Bewsher; K Theis; G Chana; A Giri. People eat rice and drink water—not soil—so why is arsenic in rice and water so under regulated in the UK compared to arsenic in soil? Arsenic in the Environment - Proceedings 2016, 275 -276.
AMA StyleD Polya, A Bualy, Andrew Speak, P Lythgoe, A Bewsher, K Theis, G Chana, A Giri. People eat rice and drink water—not soil—so why is arsenic in rice and water so under regulated in the UK compared to arsenic in soil? Arsenic in the Environment - Proceedings. 2016; ():275-276.
Chicago/Turabian StyleD Polya; A Bualy; Andrew Speak; P Lythgoe; A Bewsher; K Theis; G Chana; A Giri. 2016. "People eat rice and drink water—not soil—so why is arsenic in rice and water so under regulated in the UK compared to arsenic in soil?" Arsenic in the Environment - Proceedings , no. : 275-276.
Urban areas, in particular, present unique challenges for the conservation of ecosystems. Allotment gardens (AGs) are an important greenspace feature of urban landscapes in Europe which have the potential to offer multiple social and bio-physical ecosystem services in addition to food production. This study is an attempt to assess and compare the ecosystem services provided by AGs in Manchester, UK, and Poznań, Poland as well as a comparison to city parks. The surveys included a detailed land cover characterisation and an assessment of cultivated and spontaneous plant species. There are differences in the land use characteristics in the two cities with a preference for vegetable growing and water recycling in Manchester, and a greater number of trees and a higher focus on recreation in Poznań. The consequences of these basic differences are discussed in terms of the ecosystem services that are provided by the two different AG types, and parks. In terms of ecology, there is higher species richness on AGs with a greater proportion of neophytes, which may potentially spread into cities. The species recorded in parks and AGs contained a lot of native characteristics of urban, ruderal plant communities.
A.F. Speak; Andrzej Mizgajski; J. Borysiak. Allotment gardens and parks: Provision of ecosystem services with an emphasis on biodiversity. Urban Forestry & Urban Greening 2015, 14, 772 -781.
AMA StyleA.F. Speak, Andrzej Mizgajski, J. Borysiak. Allotment gardens and parks: Provision of ecosystem services with an emphasis on biodiversity. Urban Forestry & Urban Greening. 2015; 14 (4):772-781.
Chicago/Turabian StyleA.F. Speak; Andrzej Mizgajski; J. Borysiak. 2015. "Allotment gardens and parks: Provision of ecosystem services with an emphasis on biodiversity." Urban Forestry & Urban Greening 14, no. 4: 772-781.
Andrew Speak. Influence of vegetation damage on urban cooling effects. Eco-Efficient Materials for Mitigating Building Cooling Needs 2015, 325 -347.
AMA StyleAndrew Speak. Influence of vegetation damage on urban cooling effects. Eco-Efficient Materials for Mitigating Building Cooling Needs. 2015; ():325-347.
Chicago/Turabian StyleAndrew Speak. 2015. "Influence of vegetation damage on urban cooling effects." Eco-Efficient Materials for Mitigating Building Cooling Needs , no. : 325-347.
Runoff and rainfall quality was compared between an aged intensive green roof and an adjacent conventional roof surface. Nutrient concentrations in the runoff were generally below Environmental Quality Standard (EQS) values and the green roof exhibited NO3(-) retention. Cu, Pb and Zn concentrations were in excess of EQS values for the protection of surface water. Green roof runoff was also significantly higher in Fe and Pb than on the bare roof and in rainfall. Input-output fluxes revealed the green roof to be a potential source of Pb. High concentrations of Pb within the green roof soil and bare roof dusts provide a potential source of Pb in runoff. The origin of the Pb is likely from historic urban atmospheric deposition. Aged green roofs may therefore act as a source of legacy metal pollution. This needs to be considered when constructing green roofs with the aim of improving pollution remediation.
Andrew Speak; J.J. Rothwell; Sarah Lindley; C.L. Smith. Metal and nutrient dynamics on an aged intensive green roof. Environmental Pollution 2014, 184, 33 -43.
AMA StyleAndrew Speak, J.J. Rothwell, Sarah Lindley, C.L. Smith. Metal and nutrient dynamics on an aged intensive green roof. Environmental Pollution. 2014; 184 ():33-43.
Chicago/Turabian StyleAndrew Speak; J.J. Rothwell; Sarah Lindley; C.L. Smith. 2014. "Metal and nutrient dynamics on an aged intensive green roof." Environmental Pollution 184, no. : 33-43.
Urban areas are characterised by large proportions of impervious surfaces which increases rainwater runoff and the potential for surface water flooding. Increased precipitation is predicted under current climate change projections, which will put further pressure on urban populations and infrastructure. Roof greening can be used within flood mitigation schemes to restore the urban hydrological balance of cities. Intensive green roofs, with their deeper substrates and higher plant biomass, are able to retain greater quantities of runoff, and there is a need for more studies on this less common type of green roof which also investigate the effect of factors such as age and vegetation composition. Runoff quantities from an aged intensive green roof in Manchester, UK, were analysed for 69 rainfall events, and compared to those on an adjacent paved roof. Average retention was 65.7% on the green roof and 33.6% on the bare roof. A comprehensive soil classification revealed the substrate, a mineral soil, to be in good general condition and also high in organic matter content which can increase the water holding capacity of soils. Large variation in the retention data made the use of predictive regression models unfeasible. This variation arose from complex interactions between Antecedant Dry Weather Period (ADWP), season, monthly weather trends, and rainfall duration, quantity and peak intensity. However, significantly lower retention was seen for high rainfall events, and in autumn, which had above average rainfall. The study period only covers one unusually wet year, so a longer study may uncover relationships to factors which can be applied to intensive roofs elsewhere. Annual rainfall retention for Manchester city centre could be increased by 2.3% by a 10% increase in intensive green roof construction. The results of this study will be of particular interest to practitioners implementing greenspace adaptation in temperate and cool maritime climates.
A.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. Rainwater runoff retention on an aged intensive green roof. Science of The Total Environment 2013, 461-462, 28 -38.
AMA StyleA.F. Speak, J.J. Rothwell, S.J. Lindley, C.L. Smith. Rainwater runoff retention on an aged intensive green roof. Science of The Total Environment. 2013; 461-462 ():28-38.
Chicago/Turabian StyleA.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. 2013. "Rainwater runoff retention on an aged intensive green roof." Science of The Total Environment 461-462, no. : 28-38.
Green roofs are increasingly being utilised as urban climate adaptation measures given good evidence of their passive cooling effects. Shading of conventional building surfaces, higher albedo and latent cooling from evapotranspiration mean that vegetated surfaces can be used to significantly lower surface and air temperatures in cities. The extent to which cooling properties may be affected by poor maintenance, green roof damage and the general health of the vegetation is not as well known. This study investigates the ability of an intensive green roof in Manchester, UK, to cool the air above it relative to an adjacent conventional, concrete roof. The monthly median air temperature was found to be 1.06 °C lower at 300 mm over the green roof. Diurnal trends were apparent, with strongest cooling of 1.58 °C, occurring at night when Urban Heat Islands are most common. A section of green roof was damaged by mismanagement in a drought period, which allowed an investigation into the impairment to the cooling effect when large areas of bare substrate are present. Daytime temperatures were higher over this section of the roof than over an adjacent healthy green roof, being a maximum 0.63 °C warmer than the bare roof on average, in the late morning. Cooling still occurred at night, albeit with a lower maximum average relative cooling of 0.78 °C. Implications of the spatial influence of green roof cooling are discussed along with the need to undertake careful maintenance and irrigation of the roofs for the benefits to be maintained.
A.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. Reduction of the urban cooling effects of an intensive green roof due to vegetation damage. Urban Climate 2013, 3, 40 -55.
AMA StyleA.F. Speak, J.J. Rothwell, S.J. Lindley, C.L. Smith. Reduction of the urban cooling effects of an intensive green roof due to vegetation damage. Urban Climate. 2013; 3 ():40-55.
Chicago/Turabian StyleA.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. 2013. "Reduction of the urban cooling effects of an intensive green roof due to vegetation damage." Urban Climate 3, no. : 40-55.
Urban particulate pollution in the UK remains at levels which have the potential to cause negative impacts on human health. There is a need, therefore, for mitigation strategies within cities, especially with regards to vehicular sources. The use of vegetation as a passive filter of urban air has been previously investigated, however green roof vegetation has not been specifically considered. The present study aims to quantify the effectiveness of four green roof species – creeping bentgrass (Agrostis stolonifera), red fescue (Festuca rubra), ribwort plantain (Plantago lanceolata) and sedum (Sedum album) – at capturing particulate matter smaller than 10 μm (PM10). Plants were grown in a location away from major road sources of PM10 and transplanted onto two roofs in Manchester city centre. One roof is adjacent to a major traffic source and one roof is characterised more by urban background inputs. Significant differences in metal containing PM10 capture were found between sites and between species. Site differences were explained by proximity to major sources. Species differences arise from differences in macro and micro morphology of the above surface biomass. The study finds that the grasses, A. stolonifera and F. rubra, are more effective than P. lanceolata and S. album at PM10 capture. Quantification of the annual PM10 removal potential was calculated under a maximum sedum green roof installation scenario for an area of the city centre, which totals 325 ha. Remediation of 2.3% (±0.1%) of 9.18 tonnes PM10 inputs for this area could be achieved under this scenario.
A.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. Urban particulate pollution reduction by four species of green roof vegetation in a UK city. Atmospheric Environment 2012, 61, 283 -293.
AMA StyleA.F. Speak, J.J. Rothwell, S.J. Lindley, C.L. Smith. Urban particulate pollution reduction by four species of green roof vegetation in a UK city. Atmospheric Environment. 2012; 61 ():283-293.
Chicago/Turabian StyleA.F. Speak; J.J. Rothwell; S.J. Lindley; C.L. Smith. 2012. "Urban particulate pollution reduction by four species of green roof vegetation in a UK city." Atmospheric Environment 61, no. : 283-293.