Urban Street Trees Research Articles

Interesting and new street tree species for European cities

Effects of climate change lead to decreasing vitality and increase mortality risk for many native tree species growing under harsh environmental conditions in towns and cities. Taking into account the risks of invasiveness, practical management and scientific experience alternative species and rising floristic biodiversity may help to reduce vulnerability of urban green space. 
 Regardless of the emotional debate considering foreign species, the potential of urban street tree species originating from China may be considered for European urban places in particular in regions with expected drier and hotter conditions. The selection of 40 commonly used Chinese tree species took as its starting point observations and local experiences of five research expeditions between 2009 and 2016 concentrating on the metropoles of Shanghai, Beijing, Hangzhou, Wuxi, Jinan, and Fuyang. For the considered species only little practical and scientific knowledge is available for Central Europe.

Technosols made with various urban wastes showed contrasted performance for tree development during a 3-year experiment

Vegetation in urban areas is generally living in a stress-inducing environment. Sustaining good soil quality is crucial to improve tree development and heath in such (artificial) environment. This study investigates the dynamics of the physico-chemical properties of Technosol, and compares tree development performances in various waste mixtures. A 3-year experiment was conducted with Acer platanoides L. grown in three distinct constructed soils, in three replicates, in 0.480-m3 lysimeters in Angers (France). Four combinations of artefacts were studied either as “growing material” (GM) or “structural material” (SM). Three different SMs were used: (1) a mixture of fine mineral material, demolition rubble and green waste (SM-DR/GW), (2) a mixture of fine mineral material, track ballast and sewage sludge (SM-TB/SS), and (3) the SM currently used by Angers city for green space settlements (SM-CT). Waste characteristics and mixing proportions both affected tree development. Physical properties were not a limiting factor for tree development, despite a relatively low soil water reservoir due to high stone content. Moreover, the chemical properties of the materials, more particularly low water pH and CEC, led to poor tree development in SM-CT, whereas the other two SMs did not affect tree development. SM-TB/SS was the most suitable constructed soil after 3 years because it exhibited satisfactory soil nutrient contents that promoted the best tree crown quality. Waste mixtures can sustain soil functions for tree development. As for urban street tree pits that are 2–8 m3 in volume, soil water, and nutrient autonomy should satisfactorily sustain tree development.

Factors Influencing Hazardous Street Trees at Selected City Council in Malaysia

Street trees are an important part of city development. Proper tree management provides conducive environment for socialization. Previous research revealed the social factors and hazards associated with urban street trees but the elements that influence was not known. The objectives are: to investigate the elements of the social factors and to determine the influence of these elements towards hazardous street trees.480 questionnaires distributed among expert and public within 9 city councils. The findings revealed that 5 elements that influence the hazardous street trees; uncontrollable street planting, tree vandalism, near to neighbourhood context, lack of public awareness and poor nursery stock and failure care.

Ecohydrological model for the quantification of ecosystem services provided by urban street trees

Urban green spaces have been recognized as an important source of ecosystem services, whose quantification requires the determination of quantities related to energy, water, carbon and soil nutrient content. In this paper we propose a stochastic ecohydrological model that couples two existing models for water and nutrients in urban soil at the single street-tree scale. The model input are rainfall and irrigation, for water, and deposition and fertilization, for nitrogen, while the output are evapotranspiration, runoff and deep percolation, for water, and plant uptake and leaching, for nitrogen. The various terms are related to the amount of paved and impervious surfaces that surround the tree trunk and regulate the water and nutrient fluxes in and out the soil. Particular attention is paid to the effects of seasonal variations on plant water and nutrients through a temporal variation of the hydrologic variables (i.e., temperature and rainfall intensity and frequencies). The average model outputs are preliminarily compared with the scant existing literature data, supporting the model application to cities with different climatic conditions. The model results are used to estimate the potential for ecosystem services like tree cooling effects, soil carbon sequestration or storm-water management. Because of the minimal structure of the proposed model, it requires a very low amount of data, while accounting for the stochastic input of rainfall. In the context of climate change and increasing urbanization, the model may offer useful indications to urban planners to enhance ecosystem services while minimizing irrigation, fertilization and their related costs.

Is All Urban Green Space the Same? A Comparison of the Health Benefits of Trees and Grass in New York City.

Living near vegetation, often called “green space” or “greenness”, has been associated with numerous health benefits. We hypothesized that the two key components of urban vegetation, trees and grass, may differentially affect health. We estimated the association between near-residence trees, grass, and total vegetation (from the 2010 High Resolution Land Cover dataset for New York City (NYC)) with self-reported health from a survey of NYC adults (n = 1281). We found higher reporting of “very good” or “excellent” health for respondents with the highest, compared to the lowest, quartiles of tree (RR = 1.23, 95% CI = 1.06–1.44) but not grass density (relative risk (RR) = 1.00, 95% CI = 0.86–1.17) within 1000 m buffers, adjusting for pertinent confounders. Significant positive associations between trees and self-reported health remained after adjustment for grass, whereas associations with grass remained non-significant. Adjustment for air pollutants increased beneficial associations between trees and self-reported health; adjustment for parks only partially attenuated these effects. Results were null or negative using a 300 m buffer. Findings imply that higher exposure to vegetation, particularly trees outside of parks, may be associated with better health. If replicated, this may suggest that urban street tree planting may improve population health.

The influence of sidewalk replacement on urban street tree growth

Interactions between tree roots and sidewalks can result in damage to sidewalks and when sidewalk damage is repaired adjacent tree roots are often severed. The objective of this study was to quantify the growth response of urban trees in restricted planting spaces pre- and post-sidewalk construction. The research included four trees species commonly planted along streets in Minneapolis and Saint Paul, Minnesota, USA. Species included were: Acer platanoides, Celtis occidentalis, Gleditsia triacanthos, and Tilia spp. Two street tree populations were sampled: trees adjacent to replaced sidewalk panels (<1.75m) and trees on streets with sidewalk construction that were greater than 3m from replaced sidewalk sections. In total, increment core samples from 292 trees were analyzed. Annual rings from each tree were measured and converted to basal area increment (BAI) for analysis. Comparisons of BAI were conducted between the two sample populations to assess differences in tree growth patterns. Pre- and post-sidewalk construction BAI was also evaluated to determine the influence of construction on growth trajectory. Growth response was quantified using resistance, resilience, and recovery indices. Species were found to differ in their response to construction disturbance. Planting space width was also found to influence post-construction growth. Tilia spp. had the highest resilience and fastest overall growth recovery post-sidewalk construction and A. platanoides exhibited the lowest resistance, resilience, and recovery post-sidewalk construction.

Social Factors Influencing Hazardous Street Trees at Selected City Council in Malaysia

Street trees are an important part of city development. Proper tree management provides conducive environment for socialization. Previous research revealed the social factors and hazards associated with urban street trees but the elements that influence was not known. The objectives are: to investigate the elements of the social factors and to determine the influence of these elements towards hazardous street trees.480 questionnaires distributed among expert and public within 9 city councils. The findings revealed that 5 elements that influence the hazardous street trees; uncontrollable street planting, tree vandalism, near to neighbourhood context, lack of public awareness and poor nursery stock and failure care.Keywords: Street trees; hazards; influencing; failure trees;© 2017. The Authors. Published for AMER ABRA by e-International Publishing House, Ltd., UK. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning &amp; Surveying, Universiti Teknologi MARA, Malaysia.

Importance of urban street tree policies: A Comparison of neighbouring Southern California cities

Research points to numerous benefits provided by urban street trees including qualitative and quantitative public health, economic, and environmental advantages for a city and its residents. As with other key aspects of city management that help develop municipal success, urban forestry requires foresight, commitment and planning that lead to effective policies and strategies. Good street tree management based on effective policies can maximise street tree benefits. Poorly conceived policies or the absence of effective policies can lead to the opposite result. A case study of the neighbouring cities of Loma Linda and Redlands, California illustrates this difference. The urban tree care and protection policies in these two cities have evolved differently. The differences may be attributable to contrasting municipal commitments to preservation and to best-practice management principles. Based on a comparative analysis of street tree policies of the two cities, it can be concluded that a local culture favouring tree protection and reflective guidelines and policies can result in proactive and successful management of an urban forest. Such policies also include provision for gathering data essential for strategic tree planting, care and removal.

Introduction to ecophysiological responses to environmental stresses in urban street trees

Introduction to ecophysiological responses to environmental stresses in urban street trees

THE GREEN INFRASTRUCTURE OF A HIGHLY URBANIZED NEOTROPICAL CITY: THE ROLE OF THE URBAN VEGETATION IN PRESERVING NATIVE BIODIVERSITY

We mapped and described the composition of the urban vegetation that comprises the green infrastructure of a highly urbanized Neotropical city, and discussed how it can be used to preserve and maintain urban biodiversity. Almost half of our study area is occupied by 12 types of arboreal and herbaceous vegetation, composed mostly of urban parks, gardens and street trees. Forty-one percent of the almost 90,000 street trees are composed of 10 species with only 4 native species. These results show that this urban landscape is highly heterogeneous and has a great potential for biodiversity conservation. However, management strategies are needed, such as better planning of the urban forestry. This study is the first step towards a better understanding of how this landscape influences local biodiversity, and can be used as a management tool to increase urban resilience and functionality.

Pragmatic factors outweigh ecosystem service goals in street tree selection and planting in South-East Queensland cities

Competing demands between diverse considerations and the benefits sought make urban street tree species selection an extremely complex and challenging process for municipal land and tree managers, influencing urban greening initiatives across the world as well as in Australia. This paper presents findings from a qualitative study with tree managers and other relevant officers from local municipal authorities in South-East Queensland, Australia that examined factors influencing street tree selection and planting. Participants outlined three predominant motives for planting street trees: environmental (100%), visual and aesthetic (92%), and statutory (92%). In contrast, participants identified species characteristics (100%), site factors (100%), costs (92%), and management and maintenance issues (83%) as the most important governing factors for street tree species selection. Only half of the officers noted ecosystem services (50%), along with visual and aesthetic benefits (50%) as species selection factors. Economic, health, socio-cultural and community benefits were not mentioned among the species-selection criteria. The interviews with municipal officers revealed that the parameters governing street tree species selection in South-East Queensland do not conform to the environmental and aesthetic reasons that were cited as the primary motivations for planting street trees. Local research focused on the benefits and problems of Australian street tree species may empower councils to revise their street tree policies and integrate ecosystem services and disservices as part of the process of selecting appropriate species.

High-Quality Solid Fuel Production from Leaf Litter of Urban Street Trees

Leaf litter is a growing concern for cities. Due to adherent dirt such biomass is rarely utilized nowadays but may constitute a renewable energy source for communities or private households. Leaf litter from main roads, residential areas and city centres collected by the vacuum technique or the sweeper technique was sampled and analysed for ash content and chemical composition. Ash content of leaf litter collected by the sweeping technique was higher (21.6%–40.1% dry matter, DM) than in material collected by the vacuum technique (12.0%–21.7% DM). Leaf litter from residential areas had the highest contamination (21.7%–40.1% DM), followed by main roads (20.8%–26.2% DM) and city centres (12.0%–21.6% DM). Ash content was reduced by up to 60% with a washing treatment and reached values comparable to those achieved by multiple manual rinsing, which was conducted as a reference treatment. The chemical composition of washed leaf litter could be further improved by mechanical dehydration treatment due to a reduction in harmful elements for combustion such as K, Cl, Mg and S. Heating value of leaf litter increased and the risk of corrosion and ash melting during combustion were reduced.

Microclimatic differences and their influence on transpirational cooling of Tilia cordata in two contrasting street canyons in Munich, Germany

Urban trees can help to mitigate the urban heat island through evapotranspiration. However, growing conditions in cities are heterogeneous and micrometeorological conditions in street canyons can have a large impact on a tree’s transpiration. Here we investigated a common urban street tree species Tilia cordata of different ages and sizes, planted in two contrasting street canyons in a densely built neighbourhood within the centre of Munich, Germany: Bordeaux Platz, an open green square (OGS), and Pariser Platz, a circular paved square (CPS) with similar aspect ratio≈0.5. The experiment was carried out during the exceptionally hot and dry summer of 2015. The open green square showed significantly higher wind speed and vapour pressure deficit but lower soil temperature, less negative soil moisture potential and also a smaller wind tunneling effect compared to the circular paved square. All these variables showed strong relationship with the sapflux density (Js) of trees grown at these two sites. They explain almost 78% of the variation in Js. On average Js values of the trees at Bordeaux Platz peaked to 0.30–0.35mlcm−2min−1 during the day compared to the peak values of 0.20–0.23mlcm−2min−1 for trees at Pariser Platz. Consequently, trees grown at the open green square showed higher peak cooling of 2.3kWtree−1 or 82wm−2 than at the circular paved square (1.9kWtree−1). Interestingly, nocturnal cooling was higher for trees at the circular paved square with 18% of daytime transpiration compared to 2% for trees at the open green square. The study gave new insights into the cooling benefits of urban trees planted in open green squares compared to closed and paved squares and its temporal variation.

Mass—trapping Trials of the Fall Webworm, Hyphantria cunea(Drury) (Lepidoptera: Arctiidae) ， with Synthetic Sex Pheromone in Urban Street Trees

Mass—trapping Trials of the Fall Webworm, Hyphantria cunea(Drury) (Lepidoptera: Arctiidae) ， with Synthetic Sex Pheromone in Urban Street Trees

Carbon Storage and Sequestration of Urban Street Trees in Beijing, China

Anthropogenic carbon dioxide (CO2) emissions from cities have significantly increased over the past several decades along with rapid urbanization. To what extent anthropogenic CO2 emissions generated from cities can be offset through conserving or increasing carbon (C) stored within urban areas themselves is a significant scientific question. The role of urban street trees in offsetting anthropogenic CO2 emissions still remains uncertain. Here, using data from field surveys, tree growth measurements and governmental statistical yearbooks, we estimated the C storage and C sequestration capacity of street trees in Beijing. Results showed that the C density and C sequestration rate in Beijing’s urban street trees were about 1/3 ~1/2 of the corresponding magnitudes of non-urban forests in China. However, the total C sequestration of street trees in Beijing’s urban districts was 3.1±1.8 Gg C yr-1 (1 Gg = 109 g) in 2014, equivalent to only about 0.2% of its annual CO2-equivalent emissions from total energy consumption, indicating a rather limited role in offsetting overall anthropogenic CO2 emissions.

Flexible, open-source programmes and estimating projections of urban tree benefits: A case study in Amherst, MA

Inventories of urban tree populations and affiliated analysis software are valuable, contemporary tools in use by municipalities across the globe. While software that allows users to explore the values and benefits of discrete urban tree populations may be readily available, capacity to model and project tree growth is limited. Using existing urban street tree inventory data from Amherst, MA (USA), a generic platform for tree growth modelling was developed to be implemented by the user at the source code level, called “Xylem”. Agile programmes like this provide a fast-working, extensible platform to generate tree growth projection data that can be delivered efficiently to the end user. The Amherst case study offers an example of how programmes written in Python 2.7 have application and can be readily customisable, to add value to existing tree inventory data.

Stability of containerized urban street trees

Trees are usually grown in containers in the nursery until they reach a certain size, whereupon they are transplanted to a permanent location. Infrastructure development has often led to the removal of large trees. To maintain lush foliage and trees of a size that benefit urban ecology, trees can be grown in containers. Containerized trees can be moved from one location to another, and this relocation does not require root pruning or crown-size reduction. The drawback to having trees in containers is the small and confined volume of the container, which limits tree root development and thus affects containerized tree stability. The objective of this study was to understand the failure mechanisms for and the effect of the root dimensions on the stability of containerized trees. Therefore, small-scale stability model tests were conducted which were verified using numerical and analytical models. The results identified two failure modes that were likely to occur: tree overturning and container overturning. The mode of failure was dependent on the root dimensions. When the trees had extended their roots deep into the container, the whole container would overturn in the event of failure due to increased root confinement and shear resistance of the soil. On the other hand, the main failure mechanism when there was shallow root development was the uplifting of the tree from the container while the container remained upright. The results from numerical and analytical models were consistent with those obtained during the small-scale model stability tests.

Street Tree Inventory of Campinas, Brazil: An Instrument for Urban Forestry Management and Planning

Campinas Metropolitan Region is the third richest city in Brazil. This study assesses the urban street trees of Campinas based on data from a survey performed using satellite images in the year 2011. All public domain trees in the street system were counted and separated into trees, shrubs, palm trees, and seedlings. The density of trees was obtained using the images census and expressed as trees per linear kilometer for the perimeter of the block. The number of trees per linear kilometer was grouped into nine classes of different densities for data validation. The final number of trees was estimated based on the validation’s results. The Gini coefficient shows that the number of trees per person is very irregular in city neighborhoods (i.e., Campinas has a fairer income distribution than street trees distribution). There is a lower density of trees in the downtown area, due to the high concentration of population, and in more peripheral neighborhoods, due to the lack of design planning. The results obtained here may be used to support a new setting of local priorities for planting actions aimed at urban forestry management.

Cost-Benefit Analysis for Biological Control Programs That Targeted Insect Pests of Eucalypts in Urban Landscapes of California.

As well as being planted for wind breaks, landscape trees, and fuel wood, eucalypts are also widely used as urban street trees in California. They now are besieged by exotic insect herbivores of four different feeding guilds. The objective of the current analysis was to determine the return on investment from biological control programs that have targeted these pests. Independent estimates of the total number of eucalypt street trees in California ranged from a high of 476,527 trees (based on tree inventories from 135 California cities) to a low of 190,666 trees (based on 49 tree inventories). Based on a survey of 3,512 trees, the estimated mean value of an individual eucalypt was US$5,978. Thus, the total value of eucalypt street trees in California ranged from more than US$1.0 billion to more than US$2.8 billion. Biological control programs that targeted pests of eucalypts in California have cost US$2,663,097 in extramural grants and University of California salaries. Consequently, the return derived from protecting the value of this resource through the biological control efforts, per dollar expended, ranged from US$1,070 for the high estimated number of trees to US$428 for the lower estimate. The analyses demonstrate both the tremendous value of urban street trees, and the benefits that stem from successful biological control programs aimed at preserving these trees. Economic analyses such as this, which demonstrate the substantial rates of return from successful biological control of invasive pests, may play a key role in developing both grass-roots and governmental support for future urban biological control efforts.

Delivering a Multi-Functional and Resilient Urban Forest

Tree planting is widely advocated and applied in urban areas, with large-scale projects underway in cities globally. Numerous potential benefits are used to justify these planting campaigns. However, reports of poor tree survival raise questions about the ability of such projects to deliver on their promises over the long-term. Each potential benefit requires different supporting conditions—relating not only to the type and placement of the tree, but also to the broader urban system within which it is embedded. This set of supporting conditions may not always be mutually compatible and may not persist for the lifetime of the tree. Here, we demonstrate a systems-based approach that makes these dependencies, synergies, and tensions more explicit, allowing them to be used to test the decadal-scale resilience of urban street trees. Our analysis highlights social, environmental, and economic assumptions that are implicit within planting projects; notably that high levels of maintenance and public support for urban street trees will persist throughout their natural lifespan, and that the surrounding built form will remain largely unchanged. Whilst the vulnerability of each benefit may be highly context specific, we identify approaches that address some typical weaknesses, making a functional, resilient, urban forest more attainable.