An index for tree stability assessment in urban environment (original) (raw)
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WIND STABILITY ANALYSIS OF URBAN TREES
International Symposium on Urban Tree Health, 1999
We present an analysis of the stability of urban trees under the effect of wind pressure. The modeling is led using the yield design theory from a cinematic approach ('by the exterior'). The family of ruin mechanisms retained are very simple block rotation, as in-situ observations show. We develop entirely the mechanical modeling leading to the definition of an assistance tool for the preventive maintenance. Methods to evaluate the calculation parameters are presented. To make this evaluation the most objective, we derived it from data measured on the tree and approximations based on established results in the literature. This approach is then used to build the software 'CILVA' which is presented in another paper.
Dynamic Response Characteristics of Urban Trees
2008
Currently there is little data on wind loading available to assess dynamic excitation effects by wind on trees. Wind forces are the largest forces that trees must endure, and global climate changes are likely to generate more extreme weather events that will increase the likelihood of wind damage to trees and property. Wind induced dynamic excitation in two urban trees (a She-oak and a spotted gum located on the main campuses of The University of Melbourne and Monash University, respectively) has been assessed using tri-axial accelerometers and (separately) a purpose-designed digital strain meter that measures the outer fibre movement of a trunk or branch as it bends in the wind. The measurements on these two trees were taken on the 2 April, 2008 when an approximately 1 in 20 year wind storm was experienced in Melbourne. Pluck tests were also performed on She-oak on separate near still wind occasions as a follow-up to the wind measurements. Results from a spectral based model applie...
A semi-empirical model for the effect of trees on the urban wind environment
Landscape and Urban Planning, 2017
High-density urban areas are often associated with limited outdoor natural ventilation. Given the growing call for more vegetation in cities, it is important to study the wind resistant of urban trees in order to address outdoor natural ventilation problem in the landscape planning. Currently, Computational Fluid Dynamics (CFD) simulation and wind tunnel experiment can only model the simplified street canyon with roadside trees, at the expense of intensive technical support and high computational cost. Thus, they are mostly for the research purpose only, and the impact of research outputs on the landscape planning remains low. In this study, we developed a practical semi-empirical model to provide scientific understandings for the landscape planning practice. The new model was developed based on the balance between momentum flux and the drag force of both buildings and trees on air flow. Friction velocity (u *) was modeled and validated by existing CFD and wind tunnel data, and effective frontal area density (λ f_tree) was estimated by the measured leaf area index. Effects of urban context density and trees (i.e. plant canopy density and typology) on wind environment were clarified. This research correlated the urban density and tree geometry indices with wind speed, thereby enabling planners to calculate trees' effects on airflow using their in-house data. With such new practical tool and understandings, the knowledge-based landscape planning can be conducted to introduce more trees into urban areas, while avoiding negative effects of trees on the outdoor wind environment at cities at the same time.
The Complex Issue of Urban Trees—Stress Factor Accumulation and Ecological Service Possibilities
Forests
This review paper is the first that summarizes many aspects of the ecological role of trees in urban landscapes while considering their growth conditions. Research Highlights are: (i) Plant growth conditions in cities are worsening due to high urbanization rates and new stress factors; (ii) Urban trees are capable of alleviating the stress factors they are exposed to; (iii) The size and vitality of trees is related to the ecological services they can provide. Our review shows, in a clear way, that the phenomenon of human-related environmental degradation, which generates urban tree stress, can be effectively alleviated by the presence of trees. The first section reviews concerns related to urban environment degradation and its influence on trees. Intense urbanization affects the environment of plants, raising the mortality rate of urban trees. The second part deals with the dieback of city trees, its causes and scale. The average life expectancy of urban trees is relatively low and ...
TREES IN URBAN HABITAT Authors: Hardial Singh Johl and Sarbjit Singh Bahga This is a "ground breaking" book for town planners, architects, landscapists and city planners who face the enormous task of creating and planning cities, buildings, parks and open spaces in the face of challenging unprecedented urbanization. It is an encyclopedia of knowledge on methods and techniques to solve the intricate problems of urban planning with tree plantation. This book is an excellent reference guide that cites New Delhi and Chandigarh as examples of cities where tree plantation was a priority. The book offers valuable concepts of tree planting accompanied with photographs and illustrations to describe the appropriate use of trees in different urban settings. It provides a detailed description of the fundamental requirements of tree plantation around roads, buildings, open spaces and parks taking into account the important considerations pertaining to the structure and textures of trees, their density and diversity in growth patterns, scale, colour, form and detail. The book includes "lessons learnt" with insights into opportunities for improvement in future planning and development. The one chapter pertaining to the concept of developing the entire city into a park makes this book unique and creative.
Potential tree species for use in urban areas in temperate and oceanic climates
Heliyon, 2016
This study aims to assess the potential of trees for integration in urban development by evaluating the damage caused by trees in relation to various tree characteristics. Tree damage to permeable pavement systems and other urban structures such as impermeable pavements, kerbs, roads, retaining walls, footpaths, walls and buildings were assessed to identify the most suitable trees for the urban environment. One hundred square sites of 100 m × 100 m were randomly selected in Greater Manchester for this representative example case study to demonstrate the assessment methodology. Among tree species in this study, Acer platanoides L. (Norway maple) occurred most frequently (17%); others were Tilia spp. L. (Lime; 16%), Fraxinus excelsior L. (common ash; 12%), Acer pseudoplatanus L. (sycamore; 10%) and Prunus avium L. (wild cherry; 8%). The study concludes that 44% of the damage was to impermeable pavements and 22% to permeable pavements. Other damage to structures included kerbs (19%), retaining walls (5%), footpaths (4%), roads (3%) and walls (3%). Concerning the severity of damage, 66% were moderate, 21% light and 19% severe. Aesculus hippocastanum L. (horse chestnut) caused the greatest damage (59%) expressed in percentage as a ratio of the tree number related to damage over the corresponding tree number that was found close to structures.
Trees for Tough Urban Sites Learning from Nature
2012
The main body of work in this thesis was to develop and test a working procedure for identification of new tree species and genotypes that holds the potential to diversify urban tree populations. This process has been set in context through a literature review which characterise species-specific information about the tolerance of trees to the environmental stresses in urban paved sites. With a Scandinavian focus, a review of literature was made in order to characterise species-specific information concerning site tolerance for urban paved environments as it is disseminated in scientific papers, dendrology literature, books addressing plant use in urban environments, plant nursery catalogues. The information was evaluated against the requirements of urban tree planners which should ideally be; contextual; local, referring to existing urban plantings, specify the urban site type(s) for which a given species can be recommended, and include the full range of tree species that are well a...
Urban trees – their impacts and roles in the urban forest
Arboricultural Journal, 2019
Urban treestheir impacts and roles in the urban forest Presenting three major papers this is the fourth and final issue of the Arboricultural Journal for 2019. One paper considers root intrusions and damage, one the problems of assessing street-tree condition in the absence of effective, professional arboriculture, and one the ecosystem services provided by a widely-planted non-native tree. Damage by intrusive street-tree roots is a big issue as trees become urbanised and as planted street-trees are used to improve local environmental conditions. In this context, tree roots often intrude into sewerage pipes and storm-water drains to cause potential damage. Dealing with such intrusions may be expensive for local authorities and agencies such as utility companies. Therefore, finding ways to identify individual trees responsible for damage can be helpful but so far has proved problematic. Effective but non-destructive identification of trees with intrusive roots can help reduce costs and target resources to best effect. Fransson (2019) investigates the potential for using the concentrations in tree tissues, of eight heavy metals (silver, gold, cadmium, lead, palladium, rubidium, antimony, and zinc) and of potassium in identifying whether the tree roots were intrusive into sewer pipes or storm-water drains. Meunpong, Buathong, and Kaewgrajang (2019) take a view of the issues for street-tree evaluation and management in a major emerging urban area, namely the city of Bangkok in Thailand. The context for the study is the Bangkok Metropolitan Area (BMA), Thailand's capital city. This has around 1,200 kilometres of main roads and side-streets with about 103,000 large trees along these, and in other public spaces. However, despite the obvious need for these trees to be monitored, assessed, and managed for things like public safety or nuisance reasons, little arboricultural work is done. The trees require professional management to avoid unnecessary and potentially catastrophic fall or dropping of trunks and branches. With tropical storms and the like, there is a serious risk of injury or damage to property; and so it is surprising that so little is done within the BMA, in terms of managing its street-tree resource. This paper seeks a cost-effective way to evaluate the condition of these trees by means of Google Street View (GSV) imagery. Interestingly, comparison of the GSV survey information with data gathered and verified in the field showed a high degree of agreement in evaluating both genus and species. However, the approach was far less useful and reliable in the assessment of overall risk of failure or other associated damage. The ability of the method in identifying the overall crown risk, tree defects, and size was very limited. Ramírez and Kallarackal (2019) examine the status and ecological behaviour of Magenta Lilly Pilly tree (Syzygium paniculatum) a species widely introduced and planted in Bogotá, Colombia. This tree is now an important component of the Bogotá urban forest system and therefore it is informative to gain a better understanding of its contributions to potential ecosystem services like pollination, perching sites, and food for birds. Magenta offers a constant supply of nectar and pollen for bees though it seems that honeybees were the only insects recorded as visiting the fully-opened flowers. The native bird species, the great
Correlation of wind speed and root plate tilt of trees in urban environment
This study describes a simple method to estimate the correlation between root plate tilt and wind speed. The objective was to test if the tilt of trees in high winds can be predicted based on data obtained in the more often occurring low or mid wind events. Our conclusions are: - There is a correlation of wind speed and root plate tilt. - The correlation can be described with an e-function or power-function. - This best-fit line can be understood as an individual tree's specific tipping curve - Regional wind data can be used to calculate the wind-tilt relation. However, the smaller the distance between tree and weather station is, the better is the result. - These wind-tilt curves show the reaction of the tree to the regional wind, including tunneling or sheltering effects of other trees or buildings. - The wind direction does affect the wind-tilt curve. - Deciduous trees: the variation between summer and winter wind-tilt curve is tree species dependent. - Tilt of > 0,2° at wind speed of 50-60 km/h leads to critical tilt values at gale winds.