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| To advance the science of arboriculture for the public benefit |
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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.
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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.