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| To advance the science of arboriculture for the public benefit |
The Arboricultural Journal
The Arboricultural Journal is published quarterly and issued free to members of the Arboricultural Association. It contains valuable technical, research and scientific information about all aspects of arboriculture. The Arboricultural Journal is edited by an editorial board of 14 eminent professionals from 8 different countries.
Become a member and receive the Arboricultural Journal free of charge
List of Authors
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DANGEROUS TREES?
John Adams*
Abstract
This is a modified version of a paper prepared for a conference on The Future of Tree Risk Management, held in London on 15 September 2006.
Britain, in the view of former Prime Minister Blair, is “in danger of having a wholly disproportionate attitude to the risks we should expect to run as a normal part of life. … The result is a plethora of rules, guidelines, responses to ‘scandals’ of one nature or another that ends up having utterly perverse consequences.” My introduction to the world of tree risk management in Britain leads me to the conclusion that it is disproportionately risk averse and is having “utterly perverse consequences”.
THE EVOLUTION OF RISK ASSESSMENT AND RISK MANAGEMENT: A BACKGROUND TO THE DEVELOPMENT OF RISK PHILOSOPHY
David J. Ball*
Abstract
The usage of risk-based approaches can be traced back over millennia, but seemingly experienced surges during the era referred
to as The Enlightenment in the 18th century and again at the close of the 20th century. The widespread application of
risk-based thinking is thought by many to have yielded benefits, but across the spectrum of applications many controversies
have been identified. Risk decision makers should be aware if not wary of the potential problems to which these controversies
can give rise.
WHY RISK ASSESSMENT NEEDS AN UNDERPINNING PHILOSOPHY
David J. Ball*
Summary
Without a philosophy risk assessments cannot be interpreted and thus may be wrongly applied. The United Kingdom has evolved
a sophisticated philosophy of decision making over two centuries although this is surprisingly little known outside of
professional circles. This paper describes the philosophy and its connection with case law. It may also be possible to apply
this philosophy to the issue of the level of risk assessment which is appropriate in given circumstances, for example,
to arboriculture.
I’LL MANAGE RISK MY WAY
David J. Ball*
Summary
Those responsible for hazards have, under English law, a great deal of freedom to decide how to act, but with that freedom
goes responsibility. The requirement is to do what is reasonable and not more than that. To achieve this duty holders need to
be proactive, in touch with government thinking, aware of societal pressures and research, and to keep an eye on both
day-to-day activities and strategic objectives, to prevent these from drifting apart. Various activities are suggested which
can help bring this about.
TOWARDS A NATIONAL STANDARD FOR TREE RISK INSPECTIONS
Nick Eden*
Summary
The need for tree inspections for the purpose of safety assessments is justified in this paper by the author’s experience of
being responsible for a tree that failed and caused a fatality. It also appears to be endorsed by a number of recent high
profile cases. The need for standardised tree inspection and safety assessment methodology and associated training is presented
as a result of the author’s experience in Court and a survey conducted by Lantra Awards in 2005. A description of two
tree inspection and safety assessment training courses at basic and professional levels available from Lantra Awards is
presented along with the steps they went through in the development process.
It is generally accepted that passing the examination that is part of the professional tree inspection course, is evidence of
the competence of tree inspectors who make the final decision on tree safety issues.
MOVING THE FOCUS FROM TREE DEFECTS TO RATIONAL RISK MANAGEMENT – A PARADIGM SHIFT FOR TREE MANAGERS
Mike Ellison*
Summary
In the United Kingdom, the risk of death or serious harm from tree failure is extremely low yet the fear of litigation often
results in a disproportionate allocation of resources to the survey, inspection and treatment of trees. Frequently, the presence
of decay or defects will be cited to justify the removal and pruning of trees without adequate consideration of the often
very limited risks associated with the condition.
By employing appropriate risk management techniques and by moving the initial focus away from tree defects and onto targets,
tree managers can cost-effectively manage tree safety within the realms of reasonable practicability whilst optimising the
multiple benefits conferred by the tree resource.
Keywords:
target · reasonable practicability · risk of significant harm · defect-led · expert
TOWARDS REASONABLE TREE RISK DECISION-MAKING?
Neville Fay*
Summary
While we are all continuously exposed to risks the legal expectation is that risks need not be removed but rather should
be reasonably controlled. For tree risk management to be defendable, it is important to be able to review how risk decisions
are made (how risks are identified, appraised and controlled). Though these activities form the basis of risk management, in
the event of an accident, any relevant records may be used to establish whether duty of care has been met. Defendable
risk regulation draws on industry guidelines and is specifically based on the presumption that the time, money and effort
expended in meeting risk reduction should not be grossly disproportionate to the improvement in safety obtained.
When risks are of such a low order that they are regarded as insignificant they are considered ‘broadly acceptable’. A
reasonable framework for risk decision-making would probably regard intervention to reduce broadly acceptable risks as unwarranted. Average annual tree-related deaths from structural failure in the UK are so few that, arguably, any expenditure targeted to
avoid such risks might be considered unnecessary, given the limited benefit in risk reduction likely to be achieved. Yet, when
harm arises from tree failure, those responsible for trees carry the weight of potential investigation by the police and the
Health and Safety Executive, not to mention from civil litigation. When a tree-related death occurs a disproportionately high
level of media interest tends to follow and sometimes this is also accompanied by a landmark legal case. While such
circumstances are in some respects understandable (as rarity influences public interest), this can have an unreasonable
influence on expectations of routine tree inspection standards, and expenditure on management, and, moreover, result in
undesirable implications for the nation’s mature tree stock (loss of habitat, amenity, wilderness, carbon sink, etc.). To
counter such defensive behaviour, an important role exists for the arboricultural industry – to work with other stakeholders
to influence more rational outcomes. Such an initiative would make possible a more confident, defendable, professional stance
for the benefit of sensible risk management policies and would contribute more widely to the long term sustainability of
the nation’s trees and the ecosystem.
CURRENT ISSUES IN ARBORICULTURAL RISK ASSESSMENT AND MANAGEMENT
David Lonsdale*
Summary
People who own or manage trees are increasingly required to implement systems for assessing and managing risk. Fears which
arise from a greater awareness of responsibility and of technical requirements can be allayed by the sense of confidence that
a good system of tree risk management can provide. Both the tree inspection regime and its implementation need to be good, as
shown by recent legal cases. Good practice is being aided not only by the application of risk assessment principles, but also
by advances in technology. Advanced devices should, however, be used only when appropriate and when their users have the
necessary competence and knowledge. The cost of managing risks from trees can be considerable, both financially and in terms of
the loss of value provided by trees. It is therefore important to work towards an holistic evaluation in which trees and
their associated risks are viewed alongside everyday things which carry both value and risk. To this end, arboriculturists need
to engage with members of the risk analysis profession.
THE MANAGEMENT OF RISK WITH RESPECT TO CULTURAL HERITAGE – A CASE STUDY
John M. Watt*
Summary
Risk management at a strategic level operates to try to establish consensus in the face of uncertainty or conflict (or often both). Risks are taken in specific contexts, which relate to the aims and values of the organisation or society within which they operate. It is therefore crucial to identify the objectives of the organisation in order to identify and assess the things that threaten
the achievement of these objectives (i.e. the risks). It is therefore wrong to define ‘risk management’ as managing human
safety alone, which seems to have assumed an undue weight in some instances. A wider definition is:
"Risk: A situation or event in which something of human value (including humans themselves) has been put at stake and
where the outcome is uncertain"(Rosa, 1998).
The concept of objective in risk taking is embedded in the human value part of the definition. We are only interested in risk
where there is a decision to make because we (or somebody) desire a particular outcome. There are many desirable outcomes in
tree risk management, only one of which is safety.
The care of cultural heritage objects represents an area where management of safety may conflict with management of the very
things that people value in heritage – things that are ‘measured’ on very different scales, such as artistic integrity, patina
of age or religious practice. While some of the things that threaten an object, such as air pollution, may be
measured quantitatively, values are typically not so easy to capture in this way. This paper looks to the experience of
heritage management to illuminate some of the challenges faced by strategic management of trees and to suggest ways that
the benefits of trees may be brought more effectively into the debate on resource allocation for tree risk management. It
suggests that defining ‘acceptable risk’, a central task of risk management, should not be based on safety issues alone.
PUTTING A VALUE ON TREES: AN ECONOMIST’S PERSPECTIVE
Colin Price
Summary
Economists try to put a monetary value on trees to aid rational decisions about scarce resources. Examples exist of all the eight general methods of valuing non-market products. All methods encounter problems, to do with what is valued, by whom, from what perspective; how subjectivity influences value, and how values are scaled or partitioned according to circumstance. For a value which is so context-sensitive, an appropriate valuation protocol involves expertise drawing upon more than one method: expert aesthetic judgement calibrated by reference to the relevant population; choice experiments to establish a cardinal scale of value; and reference to data on population preferences revealed in house purchase and travel decisions. A rough indicative valuation of amenity trees in the UK was £50 000 000 000 over a 100 year period.
Keywords:
environmental valuation, stated preference, revealed preference, subjectivity
PUTTING A VALUE ON TREES – CTLA GUIDANCE AND METHODS
Scott Cullen
Summary
Arboriculturists and urban foresters frequently need to put a monetary value on amenity trees. There is interest in the UK in exploring various alternatives to currently familiar valuation methods. This paper describes the basic concepts of amenity, value, valuation and amenity value to provide a conceptual framework for valuation and a well documented context within which consider one specific valuation alternative: the CTLA guidance and methods developed for amenity tree valuation in North America. The CTLA guidance and methods are grounded in generally accepted principles of professional valuation practice, rely on readily available data and are well developed and ready to use. A Regional Plant Appraisal Committee (UKI-RPAC) has introduced supplemental guidance for the region.
Keywords:
Amenity • Amenity Value • Appraisal • CTLA • Valuation • Value
HEALTH AND WELL-BEING IN WOODLANDS: A CASE STUDY OF THE CHOPWELL WOOD HEALTH PROJECT
Liz O’Brien and Hilary Snowdon
Summary
In recent debates concerned with increasing the physical and mental well-being of the British population, the natural environment has been put forward as a particularly suitable place for people to undertake a variety of physical activities. In Britain a range of projects and campaigns has been created by organisations such as the Forestry Commission, the Countryside Agency and English Nature (now Natural England), the Woodland Trust and the Royal Society for the Protection of Birds. These projects and campaigns have focused on encouraging and enabling people to use natural and green spaces for walking, cycling, tai chi and other activities. This paper describes the Chopwell Wood Health Project which was set up as a national pilot by the Forestry Commission to build an evidence base in relation to the use of woodlands for improving health and well-being. Chopwell Wood is located near to Gateshead in North East England. The evaluation of the project highlights the importance of the project leader and other individuals enthusing and enabling people to take part in the activities provided. The partnership developed for the Chopwell Project between the Forestry Commission, the health sector, and the local community played a key role in developing and delivering the work; specifically demonstrating the importance of effective partnerships. Recommendations highlight the need for concerted engagement with General Practices and health professionals; training of Forestry Commission rangers to be able to deliver health messages, and longitudinal evaluations that help to identify any long term benefits.
Keywords:
Health and well-being, woodlands, General Practitioner referral schemes, physical activity, restorative environments
DEFENCE REACTIONS AND FUNGAL COLONISATION IN FRAXINUS EXCELSIOR AND TILIA PLATYPHYLLOS AFTER STEM WOUNDING
F.W.M.R. Schwarze1, J. Grüner, M. Schubert and S. Fink
Summary
Twenty 15-year-old ash and lime trees were each wounded by creating a chainsaw cut and an increment borer hole in May 2005. After sixteen months, trees were felled, dissected and the axial extent of both wood discoloration and barrier zone formation associated with the wounds was greater in ash than in lime. Barrier zones extended only around part of the stem circumference in both species. In ash, the barrier zone consisted of 10-20 cell rows of axial parenchyma within the earlywood and a heterogeneous matrix of libriform fibres, small vessels and concentric bands of 5-40 cell rows axial parenchyma within the latewood. In lime, the barrier zone consisted of a homogeneous layer of axial and xylem ray parenchyma, in which the cell walls showed suberisation, a low cellulose content and few pits. Fungal culturing from the discoloured wood of both species yielded mainly deuteromycetes (Fungi Imperfecti). Only one basidiomycete, Polyporus squamosus, was consistently isolated. The evidently high decay-resistance features of the barrier zone of lime trees may enhance the trees ability to remain alive and intact, even when extensive decay develops within their central, poorly defended wood as a result of severe wounding. The results of the present study suggest a possible explanation why ‘wall 4’ i.e. a defensive layer that forms within the first annual growth ring after damage, is more effective in lime than in ash.
Abstracts from the Journal 31.1
UNTENABLE FAILURE CRITERIA FOR TREES:
I.THE RESIDUAL WALL THICKNESS RULE
Franz Gruber*
Summary
The Visual Tree Assessment (VTA) rule t/R = 0.32, which has been described as a universal rule of tree safety for hollow trees with full crowns is scientifically insupportable and must be rejected. Many full crown trees with t/R ratios of more than 0.32 can be broken by loading from external sources, and trees with such ratios are not necessarily safe. It can be stated that the risk of stem failure will diminish with increasing thickness of sound wood, but stem failure is significantly dependent on the loading applied to the tree, and the 0.32 rule does not take this into account. Tree safety needs to be assessed individually rather than using general “mono-parametric” safety rules. There is little scientifically tested knowledge about the complex matter of tree safety, and it seems absolutely essential to carry out research, both fundamental and applied, into this subject.
Keywords Tree failure, stem breakage, visual tree assessment (VTA), tree breakage, hollow tree, tree safety
BS 3998 RECOMMENDATIONS FOR TREE WORK;
LIKELY IMPLICATIONS OF THE NEXT EDITION
David Lonsdale
Introduction
The last edition of BS 3998 appeared in 1989 and has been followed by many innovations, not only in technology and in working practice, but also in the appreciation of the need for a clear method of deciding what type of tree work (if any) is required. There has, in particular, been a growing awareness of the value of trees for the wildlife habitats that they provide, both in life and in death. Also, there have been several changes in the law, which need to be taken into account in the next version of BS 3998.
ROOT SPACE UNDERNEATH TRAFFIC LANES
Klaus Schröder*
Summary
Tree roots need certain essential conditions for optimal growth. These include, for instance: enough space, enough ground air ventilation and moisture, sufficient amounts of macro- and micro-nutrients, as well as the existence of symbionts. However, these conditions are not always found at potential rooting zones for urban street trees. Rooting zones often lack space and the soil is often too compacted. Furthermore, the surface is sealed off with materials impermeable to water and air, thereby causing additional problems for growth.
Additional problems arise if street trees are planted in narrow central strips between traffic lanes. The tree roots are stuck between the concrete kerbstones of the lanes on both sides and in such cases the soil often consists of highly-compressed building material through which tree roots cannot grow. These are some of the reasons why many trees that are planted in such places are in a very poor condition. Similar poor development of trees is observed when trees are planted in small planting pits in highly-compacted road beds or in poor soil. In the city of Osnabrück (Germany), officers responsible for trees and arboriculture and for road construction worked together to find solutions to these problems by using novel methods for the creation of additional rooting zones for trees. The structures underneath traffic lanes are referred to as Wurzelkanäle (Root Ducts) and Wurzelkammern (Root Chambers).
GREENING THE BLACK COUNTRY: THE WORK OF THE MIDLAND REAFFORESTING ASSOCIATION IN THE EARLY TWENTIETH CENTURY
Justin Webber
Summary
In the early twentieth century a pioneering organisation, concerned with regenerating degraded land through tree planting projects, was established in the Black Country under the name of the Midland Reafforesting Association. Pre-dating a range of organisations involved in facilitating new plantations on industrial wastelands such as the Land Restoration Trust and the Forestry Commission’s Woodland Research Unit, the Midland Reafforesting Association existed for over twenty years as the driving force behind afforrestation efforts in the rapidly urbanising West Midlands Conurbation. The ideas that stimulated the formation of the M.R.A. can largely be located within an expanding global forestry sector that was becoming both more professional and more academically rigorous. However, wider developments occurring in British forestry policy in the early twentieth century did not largely serve to help the M.R.A. on a practical level. This article will attempt to explain this apparent failure as well as assessing the wider development of the Association as a unique voluntary organisation concerned with promoting the planting of trees from its establishment in 1903 to its dissolution in 1925.
TREES AND PAVEMENTS – ARE THEY COMPATIBLE?
Stephen M. Blunt
Research into the interaction of tree roots and the conditions beneath our pavements, particularly soil materials and compaction, has been carried out for Transport for London. The programme included work to allow pavement specifications to be interpreted in terms familiar to arboriculturists, work to express the requirements of trees in terms familiar to highway engineers, work to examine the performance of roots in compacted substrates including soils and construction materials, and work to establish how much water a mature tree requires from the root zone. The objective of this work, carried out between 1999 and 2002, was to contribute to new planting:paving systems which allow trees of large stature to flourish in our urban centres. This paper describes the work and the results achieved, updating an earlier paper presented in 2000 (blunt, 2001).
LIGHTNING PROTECTION AND TREES
Ben Fuest
Introduction
This research was established for the purpose of developing a better understanding of lightning protection systems specifically designed to be fitted to trees. Coming from a background in sylviculture my initial concern was to enable important and intrinsically valuable trees to be protected from damage resulting from lightning strikes. However it quickly became apparent that the protection of nearby structures and buildings that might be liable to collateral damage in the event of strike was of equal significance.
Research showed that on those occasions where lightning protection had been installed in trees, the system employed had been based upon designs originally intended for use on buildings and other essentially non-dynamic man made structures. The particular problems of installing the necessary hardware into living and growing trees did not appear to have been adequately addressed. Thus the direct effect on the tree of the installation of the required hardware is not factored in, with the result that trees are likely to be caused some degree of long-term harm in the very process of attempting to protect them.
CONFISCATION AND DELIBERATE DESTRUCTION OF OLIVE TREES IN THE WEST BANK AND GAZA AND THE EFFECT OF THIS ON THE PALESTINIAN ECONOMY
J. Hughes
Summary
The olive tree industry in Palestine is one of the unseen casualties of the conflict in the region. As the economic grip tightens on the people, agriculture is becoming more important. Men and women who travelled into Israel or surrounding countries for employment are now confined close to home because of the restrictions in movement imposed on them by an 8m high separation barrier and by the dozens of checkpoints that are now part of everyday life. These same obstructions are also one of the challenges facing the farmer in the struggle to maintain his trees, harvest and market his product. As with farmers in the rest of the world, the only resource that he has is his land and he will not leave it. The farmers are adapting to the new situation by tapping new markets in Fair Trade and speciality produce. This paper outlines some of the obstacles that have been put in their path.
THE PLACE OF TREES IN THE CITY OF THE FUTURE
Alan Simson
Abstract
Many towns and cities in the UK and on mainland Europe are at a point in the urban system life cycle when they have shifted from an industrial to a post-industrial economy, and are entering a cycle of decline. In an attempt to reverse this trend, a frenzy of ‘urban regeneration’ has broken out to try to seek new sources of prosperity to replace those that have disappeared. This is not, however, a new activity. A similar frenzy accompanied the last period of rapid urban expansion in the UK in the nineteenth century when, in order to confront rapid social, economic, cultural and environmental change, programmes of ‘urban greening’ were established, including the first public parks and the advent of street trees.
This paper suggests that in the current frenzy of post-industrial urbanism, many of the lessons learned in the nineteenth century have yet to be re-learned and up-dated for the twenty-first century, and that urban forestry/arboriculture has the potential to play a far greater role in this that it currently does.
Keywords: urban forestry, post-industrial cities, urbanisation, arborists, trees.
shoot dieback in clipped young golden leyland (cupressocyparis leylandii) trees – a physiological mechanism?
N. Taylor1, R.W.F. Cameron1, T. Blanusa1,2,*
Abstract
Shoot dieback is a problem in frequently trimmed Leyland hedges and is increasingly affecting gardeners’ choice of hedge trees, having a negative effect on a conifer nursery industry. Some damage can be attributed to the feeding by aphids, but it is unclear if there are also underlying physiological causes. In this study, we tested the hypothesis that shoot-clipping of conifer trees during adverse growing conditions (i.e. high air temperature and low soil moisture) could be leading to shoot ‘dieback’. Three-year-old Golden Leyland Cypress (x Cupressocyparis leylandii ‘Excalibur Gold’) plants were subjected to either a well-watered or droughted irrigation regime and placed in either a ‘hot’ (average day temperature = 40°C) or a ‘cool’ (average day temperature = 27°C) glasshouse compartment. Half of the plants from each glasshouse were clipped on Day 14 and again on Day 50. Measurements of soil moisture content (SMC), net CO2 assimilation rate (A), stomatal conductance (gs), branchlet xylem water potential (XWP), plant height and foliage colour were made. Within the clipped and unclipped treatments of both glasshouse compartments, plants from the droughted regime had significantly lower values for A, gs and XWP than those from the well-watered regime. However, there was no difference in these parameters between the hot and cool glasshouse compartments. The trends seen for A, gs and XWP of all treatments generally mirrored changes in SMC indicating a direct effect of water supply on these parameters. By the end of the experiment the overall foliage colour of plants from the hot glasshouse was darker than that of plants from the cool glasshouse and the overall foliage colour was also darker following shoot clipping. In general, shoot clipping led to increases in A, gs XWP and SMC. This may be due to the reduction in total leaf area leading to a greater supply of water for the remaining leaves. No shoot ‘dieback’ was observed in any treatment in response to drought stress or shoot-clipping.
Keywords: Leyland cypress, conifer, drought, high air temperature, xylem water potential, soil moisture, stomatal conductance, CO2 assimilation, plant height, foliage colour, shoot dieback, shoot clipping, pruning.
NATIONAL TREE CONDITION SURVEYS: THEIR BENEFITS AND LIMITATIONS
David Lonsdale*
Summary
The reasons for conducting national tree surveys may include the following: concerns about the effects of human activities, the need for data as a tool for management or regulatory control, the need to provide early warnings of problems, provision of data for research and a desire for greater public awareness of trees. Specific studies and surveys exemplify the importance of deciding what sort of survey is required and of taking account of the limitations of surveys, as well as their benefits. Limiting factors include the following: the quality and consistency of data collection; the difficulty of establishing a ‘baseline’ of ‘normal’ or ‘healthy’ condition when monitoring trees; the inadequacy of relatively short-term surveys for recognising changes over time; a shortage of physical or financial resources. The value of data from casebook studies, compared with survey data, is discussed.
Keywords: tree survey, monitoring, surveillance; tree condition
The Management of Major Arboricultural Incidents*
Clive Mayhew
Abstract
This paper recalls the great storm of October 1987 which swept across southern Britain and reflects upon its legacy for arboricultural crisis management. It examines how the emergency services have developed their response to major incidents in the intervening years and makes suggestions as to how a current arboricultural reaction to a major emergency might be formulated.
Keywords: Emergency planning, arboricultural response, command structures.
THE INFLUENCE OF CARBOHYDRATES, NITROGEN FertilisERS AND WATER-RETAINING POLYMER ROOT DIPS ON SURVIVAL AND GROWTH OF NEWLY TRANSPLANTED BARE-ROOTED SILVER BIRCH (BETULA PENDULA Roth.) AND EUROPEAN BEECH (FAGUS SYLVATICA L.)
Glynn C. Percival1 and Sally Barnes2
Summary
The influence of carbohydrates and slow release nitrogen fertilisers in combination with a water-retaining polymer applied as a dip to the root system of two transplant-sensitive tree species, silver birch (Betula pendula Roth.) and European beech (Fagus sylvatica L.) under field conditions was investigated. The efficacy of the treatment on growth was quantified by recording root and shoot growth and survival at weeks 8 and 24 after bud break. Improvements in tree vitality were assessed by measurement of leaf photosynthetic rates, chlorophyll fluorescence and chlorophyll content. Irrespective of species applications of a water-retaining polymer alone had no significant effect on tree survival rates or tree vitality. Results show that carbohydrates and nitrogen fertilisers singly and in mixtures when combined with a water-retaining polymer applied as a root dip at the time of planting can be used to reduce transplant losses and improve tree vitality and growth over a growing season in two difficult-to-transplant species. Although the magnitude of the response differed between species, in all cases where carbohydrates and nitrogen fertilisers were applied a decrease in the shoot:root ratio was recorded at week 8 and 24 post treatment indicating resource allocation in favour of root over leaf and shoot growth.
OVERVIEW OF THERMAL IMAGING FOR
TREE ASSESSMENT
Alessandra Catena and Giorgio Catena *
Summary
The value of thermography for trees is reviewed in relation to the needs of inspectors and diagnosticians in the fields of forestry, arboriculture and veteran tree management. Images obtained with an infrared camera allow the early detection of various kinds of alteration in trees, including bark necrosis, decay and the onset of adaptive growth in response to damage or mechanical stress. Advantages include total non-invasiveness, rapidity of use, the provision of ‘real-time’ information and the ability to work at a distance of as much as 25 m. In order to assess trees, however, the surfaces must be out of direct sunlight, free from running water and unobscured. The images do not distinguish between different kinds of alteration automatically, but they can usually be correctly interpreted in the light of appropriate knowledge and experience. The technique does not allow a truly quantitative assessment of the relative extent of decayed and sound wood, but it appears to be accurate enough to identify trees which merit either remedial action or more precise assessment.
Keywords: Tree physiology, Tree assessment, Veteran trees management, Habitat assessment, Tree decay, Tree hazard assessment, Thermography, Thermal imaging, Infrared photography, Phytophthora spp.
TREES, DAYLIGHT AND BUILDINGS
Rodney Helliwell
Summary
Whether considering the effect of trees on the amount of light beneath single trees, groups of trees, or in nearby buildings, arboriculturists need to understand the nature of daylight and how it can be affected by the location, type, and management of trees. This paper attempts to set out very briefly the relevant features of daylight and to indicate ways in which trees and buildings might successfully co-exist.
the tree owner’s duty of care and
duty of inspection
Richard Stead*
Summary
The precise duty of care of the tree owning landowner is difficult to state. The standard of inspection required is influenced by the higher standards of the arboricultural profession which may impose upon individual landowners unrealistic demands. This may lead to a defensive approach to tree management.
street trees and stormwater management
V.R. Stovin,* A. Jorgensen,† and A. Clayden†
Abstract
Urban trees play an important role in the urban hydrological cycle. Yet little consideration has been given in the UK either to the increasing pressures that act to reduce urban tree cover or the opportunities that might be provided by land-use planning policies to increase it. Research in North America, particularly by American Forests (2007), suggests that urban tree cover may be directly equated to stormwater volumes and, therefore, to the costs of providing engineered structures for stormwater management. Tree planting policies have been justified on the financial benefits associated with their stormwater management function alone, notwithstanding the broader spectrum of benefits they provide within the urban environment.
This paper presents preliminary research aimed at transferring these findings into a UK context. Two residential morphology units (RMUs) have been defined within the city of Sheffield, for which current levels of tree cover have been accurately quantified. Current tree cover levels are relatively low, but approaches to integrating more trees into these two landscape types are outlined.
Keywords: Green infrastructure, Hydrology, Interception, Rainfall, Runoff, Stormwater, Street Trees
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