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1.
Promoting the plant diversity of urban green spaces is crucial to increase ecosystem services in urban areas. While introducing ornamental plants can enhance the biodiversity of green spaces it risks environmental impacts such as increasing emissions of biogenic volatile organic compounds (BVOCs) that are harmful to air quality and human health. The present study, taking Qingdao City as a case study, evaluated the plant diversity and BVOC emissions of urban green spaces and tried to find out a solution to increase biodiversity while reducing BVOC emissions. Results showed that: (1) the species diversity and phylogenetic diversity of trees in urban green spaces were 22% and 16% lower than rural forest of this region; (2) urban areas had higher BVOC emission intensity (2.6 g C m−2 yr−1) than their rural surroundings (2.1 g C m−2 yr−1); (3) introducing the selected 11 tree species will increase 15% and 11% of species diversity and phylogenetic diversity, respectively; and (4) the BVOC emissions from green spaces will more than triple by 2050, but a moderate introduction of the selected low-emitting trees species could reduce 34% of these emissions. The scheme of introducing low-emitting ornamental species leads to a win–win situation and also has implications for the sustainable green space management of other cities.  相似文献   

2.
The implementation of trees in urban environments can mitigate outdoor thermal stress. Growing global urban population and the risk of heatwaves, compounded by development driven urban warmth (the urban heat island), means more people are at risk of heat stress in our cities. Effective planning of urban environments must minimise heat-health risks through a variety of active and passive design measures at an affordable cost. Using the Solar and Longwave Environmental Irradiance Geometry (SOLWEIG) model and working within the bounds of current urban design, this study aimed to quantify changes in mean radiant temperature (Tmrt) from increased tree cover at five different 200 × 200 m urban forms (including compact mid-rise development, residential and open grassy areas) within a suburb of Adelaide, Australia during summer. Following a successful validation of SOLWEIG, street trees were strategically distributed throughout each of the five urban forms and the model run over five warm sunny days (13–17 February 2011). Results showed spatially averaged daytime (7:30–20:00) Tmrt reduced by between 1.7 °C and 5.1 °C at each site, while under peak heating conditions (16 February, 14:00) Tmrt reduced by between 2.0 °C and 7.1 °C. The largest reduction in Tmrt under peak warming conditions was at the residential site, despite having the fewest number of trees added. Directly below clusters of trees, Tmrt could be reduced by between 14.1 °C and 18.7 °C. SOLWEIG also highlighted that more built-up sites showed higher Tmrt under peak warming conditions due to increased radiation loading from 3D urban surfaces, but over the course of the day, open sites were exposed to greater and more uniform Tmrt. This study clearly demonstrates the capacity of street trees to mitigate outdoor thermal stress and provides guidance for urban planners on strategic street tree implementation.  相似文献   

3.
We evaluated the accuracy and efficiency of airborne (ALS), terrestrial (TLS) and mobile laser-scanning (MLS) methods that can be utilized in urban tree mapping and monitoring. In the field, 438 urban trees located in park and forested environments were measured and mapped from our study area located in Seurasaari, Helsinki, Finland. A field reference was collected, using a tree map created manually from TLS data. The tree detection rate and location accuracy were evaluated, using automatic or semiautomatic ALS individual tree detection (ALSITDauto or ALSITDvisual) and manual or automatic measurements of TLS and MLS (TLSauto, MLSauto, MLSmanual, MLSsemi). Our results showed that the best methods for tree detection were TLSauto and MLSmanual, which detected 73.29% and 79.22% of the reference trees, respectively. The location accuracies (RMSE) varied between 0.44 m and 1.57 m; the methods listed from the most accurate to most inaccurate were MLSsemi, TLSauto, MLSmanual, MLSauto, ALSITDauto and ALSITDvisual. We conclude that the accuracies of TLS and ALS were applicable for operational urban tree mapping in heterogeneous park forests. MLSmanual shows high potential but manual measurements are not feasible in operational tree mapping. Challenges that should be solved in further studies include ALSITDauto oversegmentation as well as MLSauto processing methodologies and data collection for tree detection.  相似文献   

4.
Urban trees experience site-induced stress and this leads to reduced growth and health. A site assessment tool would be useful for urban forest managers to better match species tolerances and site qualities, and to assess the efficacy of soil management actions. Toward this goal, a rapid urban site index (RUSI) model was created and tested for its ability to predict urban tree performance. The RUSI model is field-based assessment tool that scores 15 parameters in approximately five minutes. This research was conducted in eight cities throughout the Midwest and Northeast USA to test the efficacy of the RUSI model. The RUSI model accurately predicted urban tree health and growth metrics (P < 0.0001; R2 0.18–0.40). While the RUSI model did not accurately predict mean diameter growth, it was significantly correlated with recent diameter growth. Certain parameters in the RUSI model, such as estimated rooting area, soil structure and aggregate stability appeared to be more important than other parameters, such as growing degree days. Minimal improvements in the RUSI model were achieved by adding soil laboratory analyses. Field assessments in the RUSI model were significantly correlated with similar laboratory analyses. Other users may be able to use the RUSI model to assess urban tree planting sites (<5 min per site and no laboratory analyses fee), but training will be required to accurately utilize the model. Future work on the RUSI model will include developing training modules and testing across a wider geographic area with more urban tree species and urban sites.  相似文献   

5.
Knowledge of allometric equations can enable urban forest managers to meet desired economic, social, and ecological goals. However, there remains limited regional data on young tree growth within the urban landscape. The objective of this study is to address this research gap and examine interactions between age, bole size and crown dimensions of young urban trees in New Haven, CT, USA to identify allometric relationships and generate predictive growth equations useful for the region. This study examines the 10 most common species from a census of 1474 community planted trees (ages 4–16). Regressions were applied to relate diameter at breast height (dbh), age (years since transplanting), tree height, crown diameter and crown volume. Across all ten species each allometric relationship was statistically (p < 0.001) significant at an α-level of 0.05. Consistently, shade trees demonstrated stronger relationships than ornamental trees. Crown diameter and dbh displayed the strongest fit with eight of the ten species having an R2 > 0.70. Crown volume exhibited a good fit for each of the shade tree species (R2 > 0.85), while the coefficients of determination for the ornamentals varied (0.38 < R2 < 0.73). In the model predicting height from dbh, ornamentals displayed the lowest R2 (0.33 < R2 < 0.55) while shade trees represented a much better fit (R2 > 0.66). Allometric relationships can be used to develop spacing guidelines for commonly planted urban trees. These correlations will better equip forest managers to predict the growth of urban trees, thereby improving the management and maintenance of New England's urban forests.  相似文献   

6.
Roads destroy natural habitats. To reduce erosion, support wildlife and decorate surroundings, ornamental trees are planted near the roadside. However, it is inadequately understood how roads influence fruit production of trees and birds that consume their fruits, within urban landscapes. During the autumn and winter of 2012–2013, we studied the extent to which birds used the fruit from rowanberry trees (Sorbus aucuparia), in two cities along a 700 km latitudinal gradient in Finland. In matched pair design (total of 35 pairs), we compared roadside trees (approximately 8 m from main roads) with trees grown away from roads (control trees; approximately >80 m from the roads). During the autumn, each rowanberry tree pair was photographed, and frugivorous birds were surveyed twice per month until all of the rowanberry fruit-crop was consumed. There was no difference in fruit crop size between roadside trees and control trees. A total of eight frugivorous bird species and 960 individuals were observed foraging in roadside trees. The three most abundant species were Bohemian waxwing (Bombycilla garrulus, 56.4%), Pine Grosbeak (Pinicola enucleator, 28.9%) and Fieldfare (Turdus pilaris, 10.5%). Total abundance and species richness of frugivorous birds were lower around roadside trees than control trees during most of the study period. Fruits were consumed later from roadside trees than from control trees, probably due to human-caused disturbance. Therefore, roadside rowanberry trees extended the period when frugivorous birds stayed in urban habitats. Later consumption of fruits in northern areas than in southern areas was related to earlier peak abundance of frugivorous birds in south than in north. Our results indicated that rowanberry is a suitable ornamental tree for urban and roadside landscaping and may additionally benefit birds and other frugivorous wildlife.  相似文献   

7.
Soil aeration is an important factor in tree growth. Oxygen must be taken from the atmosphere for root respiration, and carbon dioxide must be discharged to the atmosphere. Because the pore space of the soil could be considered the “dead end” of the free atmosphere, topsoil gas diffusivity is particularly important for soil aeration. Due to diverse land uses, several soil cover types alternate on a small scale at urban sites, competing with the natural function of soil as the living space for roots.During Documenta 7 in 1982, the artist Joseph Beuys initiated the spectacular landscape art project “7000 Oaks”. Seven thousand trees of approximately the same age were planted over the whole city of Kassel, Germany, offering best possible conditions for investigating the influence of specific site factors on root and tree development. At 8 different sites featuring 36 Beuys-oaks and 15 Beuys-planes, topsoil gas diffusivity, soil CO2 concentration and soil respiration of different soil cover types were measured and correlated with fine root density and tree growth.Topsoil gas diffusivity and soil respiration depend on soil cover type. The lowest gas diffusivities and respiration rates were found at sealed sites, and the highest values were measured at vegetated sites such as lawn or flower beds. Soil gas diffusivity primarily controls soil respiration. Soil CO2 concentration is not strictly linked to the coverage type and does not show a strictly directed dependence on top soil gas diffusivity and soil respiration. Tree root density and height as well as diameter at breast height (1.3 m) of the oaks were decisively shaped by the gas diffusivity of the soil cover, whereas the investigated planes were not affected by soil aeration deficiencies. The vitality of urban trees can be controlled by the design of the tree site and the choice of the species.  相似文献   

8.
Of interest to researchers and urban planners is the effect of urban forests on concentrations of ambient air pollution. Although estimates of the attenuation effect of urban vegetation on levels of air pollution have been put forward, there have been few monitored data on small-scale changes within forests, especially in urban forest patches. This study explores the spatial attenuation of particulate matter air pollution less than 10 μ in diameter (PM10) within the confines of an evergreen broadleaved urban forest patch in Christchurch, New Zealand, a city with high levels of PM10 winter air pollution. The monitoring network consisted of eight monitoring sites at various distances from the edge of the canopy and was operated on 13 winter nights when conditions were conducive for high pollution events. A negative gradient of particulate concentration was found, moving from higher mean PM10 concentrations outside the forest (mean=31.5 μg m?3) to lower concentrations deep within the forest (mean=22.4 μg m?3). A mixed-effects model applied to monitor meteorological, spatial and pollution data indicated temperature and an interaction between wind speed and temperature were also significant (P?0.05) predictors of particulate concentration. These results provide evidence of the potential role that urban forest patches may play in mitigating particulate matter air pollution and should be considered in plans for improving urban air quality.  相似文献   

9.
The urban forest provides valuable ecosystem services for enhancing human well-being. Its structure and composition determine the quantity and quality of these services. There has been little research on the heterogeneity in structure and composition of urban forests in the Australasian region, especially in the centre of a highly dynamic and rapidly urbanizing city. This paper quantifies the structure and the composition of the urban forest of Melbourne, Australia's city centre. The effects of land tenure and land use on the heterogeneity of canopy cover, tree density and canopy size were explored. Species and family composition by land use, land ownership and street type were also analysed using the Shannon–Wiener and Jaccard similarity indices. Most of the canopy cover in the city centre is located on public land and is unevenly distributed across the municipality. The mean canopy cover (12.3%) is similar to that found for whole city studies around the world, which often include peri-urban forests. Similarly to other cities, structure varied across different land uses, and tree size, density and cover varied with land tenure and street type. The diversity index shows that the urban forest is rich in species (H′ = 2.9) and is dominated by native species. Improving the distribution, and increasing tree cover and variety of species will result in a more resilient urban centre, able to provide multiple ecosystem services to their residents and its large population of visitors and workers. The study of the urban centre provides further understanding of compact city morphologies, and allows inter-city comparison independent of the size.  相似文献   

10.
Greening of shopping centre parking lots is a potentially important strategy that can contribute to urban carbon mitigation efforts, improve aesthetics and the shopping experience of consumers, whilst adding to urban biodiversity. Twenty-eight shopping centre parking lots in six Eastern Cape urban centres, South Africa, were sampled to determine tree species composition, density and annual carbon sequestration potential. The best case parking lot found during the study was used as a benchmark to display the difference between current tree density and above-ground carbon stocks relative to the potential optimum. The highest tree density was 66 trees ha?1, whereas the average density across all sampled parking lots was less than half that (27.2 ± 22.6 trees ha?1). The average annual carbon sequestration potential per parking lot was 1390 ± 2503 kg ha?1. Planting density was positively related to annual sequestration rates, whilst parking lot age and the mean annual rainfall of the town had no influence. Mean tree species richness per parking lot was 2.3 ± 1.8 species, with a positive relationship to parking lot size, but not to mean annual rainfall of the site. The majority of trees (62.5%) in parking lots were alien species, although newer parking lots had significantly greater proportions of indigenous species. There was no difference in mean annual carbon sequestration rate per tree between indigenous and alien trees species. Low tree densities and small parking lot areas constrained the potential for earning carbon credits from trees in parking lots. Nonetheless, planners and designers need to be more aware of the potential contribution of trees towards urban sustainability.  相似文献   

11.
Given increased atmospheric loads in cities, quantification of stemflow chemistry is necessary for a holistic understanding of elemental cycling in urban ecosystems. Accordingly, the stemflow volume and associated solute fluxes (K+, Ca2+, Na+, Mg2+) were measured for eleven deciduous trees in a manicured park setting in Kamloops, British Columbia, Canada. Over nine rainfall events from late June to early September 2013, larger trees [diameter at breast height (DBH) > 30 cm] were found to generally produce higher event stemflow volumes but lower funneling ratios than the smaller trees (DBH < 30 cm). The median flux-based enrichment ratio, which compares the solute input of stemflow to that of rainfall on a per unit trunk basal area, also tended to be greater for smaller trees than larger ones. Under all-tree and single-leader tree conditions, significant negative non-linear relationships between tree DBH and mean flux-based enrichment ratios were found for Ca2+, Na+, and Mg2+, but not for K+. These preliminary results indicate that urban trees can considerably enrich rainfall that is partitioned into stemflow, and that ion concentrations and enrichment ratios exhibit notably high interspecific variability. In this study, tree size and presence of single versus multiple leaders explained some of this heterogeneity; however, further study into those physical tree characteristics that affect stemflow volume and stemflow chemistry must be carried out if the impact and challenges of urban greening, nutrient cycling, and stormwater management initiatives are to be more fully understood.  相似文献   

12.
The chemical composition of soil and appropriate supply of nutrients are very important factors for normal plant growth and development. Lime tree (Tilia x vulgaris H.), is a popular tree species used for urban landscaping in Europe. However, there is little information on the chemical element concentrations available to and recommended for T. x vulgaris in urban soils. The objectives of this study were: (1) to investigate the amount of nutrients, de-icing salts and heavy metals available for uptake by trees in the city centre on a seasonal scale; and (2) to assess the relationship between the vitality of T. x vulgaris and soil chemistry. The research was carried out in five streets and a park in Riga (Latvia) during 2005–2007. Plant-available concentrations of 17 nutrients and heavy metals were determined via 1 M HCl extraction. Soil Cl content, pH, and electrical conductivity were also measured.The investigation revealed a high heterogeneity in soil chemical composition. In total, the element concentrations in urban soils did not exceed values commonly found in urban environments. Higher concentrations of Na, Cl, Ca, Mg, Zn, Cu, and increased pH, but lower P and B concentrations were found in the street soils in comparison to the park soil. Significantly higher concentrations of Na, Cl, and Mg, and lower concentrations of K, Fe, Cu, and B, as well as unfavourable ratios of several element concentrations were found in the soils where more damaged street trees were growing. In addition, the recommended fertilization regimes are discussed.  相似文献   

13.
This paper presents a study of mitigation of the heat island effect in the built environment with urban (city) parks. The park cooling island (PCI) effect, considering park grass cover and trees’ density and age, is determined for selected extreme summer days at various wind speeds under the optimum soil water conditions in the root zone based on an all-day quasi-stationary thermal response. PCI was determined numerically by coupling a CFD model of an urban park and quasi-steady state, two-zone thermal response boundary condition models of each park element. The boundary models are evaluated in form of multi-parameter approximation polynomials taking into account the sensible and latent heat transfer and the geometrical, optical and thermal properties of park elements. Three-dimensional CFD modelling was used for the determination of temperature, humidity and air velocity fields in an urban park with a size of 140 m × 140 m. Based on the comparison of the measured and numerically determined air temperatures in the tree crowns, we proved that the method of linking the models is adequate for temperature and flow condition modelling in the city park environment.The results are presented in the form of local PCI as the difference between local air temperature in the pedestrian zone and the reference air temperature preceding the park. The study proved that it is possible to normalise the cooling effect using the specific dimensionless coefficient of leaf area (LAIsp), which includes an approximation of the density of trees planted in the park and their size or age. It was found out that the cooling effect of the park is up to ?4.8 °C at LAIsp, equal to 3.16, which corresponds to a planting density of 45 trees per hectare, with an age of 50 years. It was also found that with the length of the park cooling effect change decreases. The optimal length of the park with a LAIsp 3 is 130 m.  相似文献   

14.
Paired aerial photographs were interpreted to assess recent changes in tree, impervious and other cover types in 20 U.S. cities as well as urban land within the conterminous United States. National results indicate that tree cover in urban areas of the United States is on the decline at a rate of about 7900 ha/yr or 4.0 million trees per year. Tree cover in 17 of the 20 analyzed cities had statistically significant declines in tree cover, while 16 cities had statistically significant increases in impervious cover. Only one city (Syracuse, NY) had a statistically significant increase in tree cover. City tree cover was reduced, on average, by about 0.27 percent/yr, while impervious surfaces increased at an average rate of about 0.31 percent/yr. As tree cover provides a simple means to assess the magnitude of the overall urban forest resource, monitoring of tree cover changes is important to understand how tree cover and various environmental benefits derived from the trees may be changing. Photo-interpretation of digital aerial images can provide a simple and timely means to assess urban tree cover change to help cities monitor progress in sustaining desired urban tree cover levels.  相似文献   

15.
Manually measuring tree root characteristics can be inefficient and limiting. To test the application of a new digital technology in tree root architecture research, root systems from 29 green ash (Fraxinus pennsylvanica 'Patmore') trees were unearthed, cleaned, and photographed to create 3D models using structure from motion (SfM) photogrammetry. Three root segments from each root system were selected, marked, and removed after being photographed. The volumes of these segments (derived from the 3D models) were compared against volumes measured using water displacement. In addition to the root segments, model and water displacement volumes were compared for three complete root systems. Regression analysis showed a strong linear relation between the two volumes measurements (adjusted R2 = 0.97 for the root segment data). The RMSE for the root segment volume estimates was 40.37 cm3 (12.3%), with a bias of 17.2 cm3 (5.3%). This error rate was similar to previous published work and suggests the technology used may allow researchers to improve efficiency in data capture, add new measurements (i.e., surface area) to their modeling efforts, and digitally preserve tree root systems for future study.  相似文献   

16.
Trees along footpath zones (or verges) grow on the “front-line” of urban forest ecosystems, increasingly recognised as essential to the quality of human life in cities. Growing so close to where residents live, work and travel, these street trees require careful planning and active management in order to balance their benefits against risks, liabilities, impacts and costs. Securing support and investment for urban trees is tough and robust business cases begin with accurate information about the resource. Few studies have accounted for spatial heterogeneity within a single land-use type in analyses of structure and composition of street tree populations. Remotely sensed footpath tree canopy cover data was used as a basis for stratification of random sampling across residential suburbs in the study area of Brisbane, Australia. Analysis of field survey data collected in 2010 from 80 representative sample sites in 52 suburbs revealed street tree population (432,445 ± 26,293) and stocking level (78%) estimates with low (6.08%) sampling error. Results also suggest that this population was transitioning to low risk, small-medium sized species with unproven longevity that could limit the capacity of the Brisbane’s Neighbourhood Shadeways planting program to expand from 35% footpath tree canopy cover in 2010, to a target of a 50% by 2031. This study advances the use of contemporary techniques for sampling extensive, unevenly distributed urban tree populations and the value of accurate resource knowledge to inform evidence-based planning and investment for urban forests.  相似文献   

17.
Accurately measuring the biophysical dimensions of urban trees, such as crown diameter, stem diameter, height, and biomass, is essential for quantifying their collective benefits as an urban forest. However, the cost of directly measuring thousands or millions of individual trees through field surveys can be prohibitive. Supplementing field surveys with remotely sensed data can reduce costs if measurements derived from remotely sensed data are accurate. This study identifies and measures the errors incurred in estimating key tree dimensions from two types of remotely sensed data: high-resolution aerial imagery and LiDAR (Light Detection and Ranging). Using Sacramento, CA, as the study site, we obtained field-measured dimensions of 20 predominant species of street trees, including 30–60 randomly selected trees of each species. For each of the 802 trees crown diameter was estimated from the aerial photo and compared with the field-measured crown diameter. Three curve-fitting equations were tested using field measurements to derive diameter at breast height (DBH) (r2 = 0.883, RMSE = 10.32 cm) from the crown diameter. The accuracy of tree height extracted from the LiDAR-based surface model was compared with the field-measured height (RMSE = 1.64 m). We found that the DBH and tree height extracted from the remotely sensed data were lower than their respective field-measured values without adjustment. The magnitude of differences in these measures tended to be larger for smaller-stature trees than for larger stature species. Using DBH and tree height calculated from remotely sensed data, aboveground biomass (r2 = 0.881, RMSE = 799.2 kg) was calculated for individual tree and compared with results from field-measured DBH and height. We present guidelines for identifying potential errors in each step of data processing. These findings inform the development of procedures for monitoring tree growth with remote sensing and for calculating single tree level carbon storage using DBH from crown diameter and tree height in the urban forest.  相似文献   

18.
Across cities worldwide, people are recognizing the value of greenspace in ameliorating the health and well-being of those living there, and are investing significant resources to improve their greenspace. Although models have been developed to allow the quantification of ecosystem services provided by urban trees, refinement and calibration of these models with more accurate site- and species-specific data can increase confidence in their outcomes. We used data from two street tree surveys in Cambridge, MA, to estimate annual tree mortality for 592 trees and diameter growth rates for 498 trees. Overall tree turnover between 2012 and 2015 was relatively low (annualized 3.6% y−1), and mortality rate varied by species. Tree growth rates also varied by species and size. We used stem diameter (DBH) and species identity to estimate CO2 sequestration rates for each of 463 trees using three different model variations: (1) i-Tree Streets, (2) Urban Tree Database (UTD) species-specific biomass allometries and growth rates, and (3) empirically measured growth rates combined with UTD biomass allometries (Empirical + UTD). For most species, the rate of CO2 sequestration varied significantly with the model used. CO2 sequestration estimates calculated using i-Tree Streets were often higher than estimates calculated with the UTD equations. CO2 sequestration estimates were often the lowest when calculated using empirical tree growth estimates and the UTD equations (Empirical + UTD). The differences among CO2 sequestration estimates were highest for large trees. When scaled up to the entire city, CO2 sequestration estimates for the Empirical + UTD model were 49.2% and 56.5% of the i-Tree Streets and UTD estimates, respectively. We suggest future derivations of ecosystem service provision models allow localities to input their own species-specific growth values. By adding capacity to easy-to-use tools, such as i-Tree Streets, we can increase confidence in the model output.  相似文献   

19.
In conjunction with urbanization and its importance as a major driver of land-use change, increased efforts have been placed on understanding urban forests and the provisioning of ecosystem services. However, very little research has been conducted on private property and little is known about the structure and function of privately owned urban forests. This research examines the structure of and carbon storage services provided by private residential urban forests in a moderate-sized Midwestern city. The primary research questions are as follows: What is the structure of private urban forests, and how does it vary across parcels? How much carbon is stored in tree and soil pools of private urban forests, and how does carbon vary across parcels? Ecological inventories were conducted on 100 residential parcels within 14 Neighborhood and Homeowners Associations of varying size and development age. Tree species richness, diversity, density, and diameter distribution were determined on a per parcel basis and for the entire tree population sampled. Further, tree and soil carbon storage were determined for each parcel. Results of this research demonstrated large variability in per-parcel tree metrics. Twelve of the parcels sampled had two or fewer trees, while eleven had greater than 50 trees. Further, tree carbon storage ranged from no carbon to 11.22 kg C m?2. Alternatively, soil carbon storage was less variable and averaged 4.7 kg C m?2, approximately 1.9 times higher than the average carbon stored in trees (2.5 kg C m?2). Management efforts aimed at maintaining or enhancing carbon storage and other ecosystem services should focus on both soil protection and maximizing services in living biomass. Our results demonstrate that sustaining tree-produced ecosystem services requires maintenance of large old trees and species diversity, not only in terms of relative abundance, but also relative dominance, and in combination, species–specific size distributions.  相似文献   

20.
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 12.1 ha, 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 ≤3 m s−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 3–5 ha, situated 100–150 m apart.  相似文献   

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