Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of the Arboricultural Association.

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Tree risk management

Author:  Jeremy Barrell
  31/05/2021
Last Updated:  31/05/2021

A legal update for arboriculturists

Jeremy Barrell

High winds can signal anxious times for those responsible for tree safety

Figure 1: High winds can signal anxious times for those responsible for tree safety.

Do you ever lay awake worrying about trees when the wind blows hard? Whether you are a duty holder responsible for tree safety or a tree specialist advising on tree management, storms can be anxious times, but it doesn’t have to be that way.1

We are often told that tree risk management is a complex subject, and in many respects that is right because it requires such a background breadth of knowledge, experience and skills. However, the task for those designing approaches to managing tree risk is to distil that complication down into simple processes that duty holders and advisors alike can understand and implement without having a doctorate in statistics or subscribing to ‘sophisticated’ proprietary methods. In that respect, arboriculture has struggled to deliver, with a raft of commercial products more focused on the exclusivity that complexity brings rather than simplicity and easy access for all. This is having a significant adverse impact on the depth and quality of our national tree resource, with practitioners often preferring to fell trees that may be a problem rather than run the risk of criticism if a failure causes harm. ‘Better safe than sorry’ works for the individual because it reduces personal risk, but it fails the wider community through loss of tree benefits.

In my new Research Article, ‘The implications of recent English legal judgments, inquest verdicts, and ash dieback disease for the defensibility of tree risk management regimes’,2 I postulate that these shortfalls originate from a well-intended desire to follow established risk management theory that seems to have gone badly wrong. I advocate that transposing an approach that evolved in rigidly controlled factory environments to trees, where the sheer variety of circumstances and lack of reliable records limit any meaningful statistical analysis, is not working very well. There is an understandable comfort in numbers, but that can be nothing more than an elusive aspiration in the practical world of trees. The Arboricultural Journal Research Article is a legal-oriented update for strategic tree managers; this ARB Magazine article supplements that overview by providing further clarifications for arboriculturists who wish to feel more at ease with their tree risk management decisions.

This ash tree has severe ash dieback
disease

Figure 2: This ash tree has severe ash dieback disease with at least 75% defoliation. Trees with this level of infection can deteriorate very quickly and must be managed more intensely than healthy trees.

Emerging issues influencing strategic tree risk management

The detailed design of a tree risk management regime is influenced by a range of factors including published legal case outcomes, new technical publications, current government guidance, emerging tree health issues that affect safety, and the building body of practical experience. This reference framework is constantly evolving as practical lessons are learnt, emerging societal preferences are expressed through court decisions, and new research is published. Recent events with the potential to significantly influence the extent of tree management expected by the courts include the following:

1. Civil judgments: These written decisions from the civil courts can be useful because they provide insights into what might be expected of duty holders. The first instance case of Cavanagh v Witley Parish Council & Shepherd3 (2017) and the later High Court Appeal4 (2018) relating to a lime tree that fell causing serious injuries to a bus driver, deal with checking frequency and occupancy issues.

2. Criminal prosecutions: Successful criminal prosecutions relating to trees are rare, and so they are important when they happen. In July 2020, the death of an infant, whose mother was struck by a falling branch while driving in Wirral, resulted in the HSE bringing a case against Wirral Metropolitan Borough Council (WMBC) at Liverpool Magistrates Court, where it pleaded guilty to breaching Section 3(1) of the Health and Safety at Work Act 1974, and was fined £100,000 and ordered to pay costs of £49,363.5

3. Prevention of future deaths (PFD) reports: Coroners have the power to issue PFD reports following inquests where they believe that future deaths could be avoided through changes to operational or management practices. Two inquests that resulted in tree-related PFD reports, Michael Arthur Warren6 (2014) and Lucia Jayne Steer7 (2019), highlighted the importance of formal corporate policies, tree hazard identification training, and fit-for-purpose management of highway trees.

4. Ash dieback disease: Ash dieback disease is progressively killing millions of ash trees across the UK (Figure 2). This is now common knowledge and duty holders failing to heed government-endorsed advice on managing the risk8 will be vulnerable to criticism and liability where unmanaged trees fail and cause harm.

Decision-making frameworks for duty holders

In practice, there is a difference between the expectations of the civil courts of duty holders who have no Health and Safety at Work Act (HSWA) obligations, e.g., homeowners, and those who have a legal duty to comply, e.g., highway authorities and corporations. The main difference is that the courts seem to support homeowners with some tree knowledge checking their own trees without specific training, while duty holders that have HSWA obligations are more likely to be expected to use experienced and trained inspectors. Establishing what the courts are likely to expect in each of these scenarios can be described in terms of the occupancy of the location, the type of check, the credentials of the inspector, and the frequency of revisiting.

Duty holders with no HSWA responsibilities

Duty holders with trees and no business interests active at their properties have no obligations under the HSWA, but they do have a duty of care under civil law to take reasonable care to avoid acts or omissions that cause a reasonably foreseeable risk of harm. In practical terms, that means trees must be checked for obvious defects that could cause harm if they failed. Figure 3 outlines a decisionmaking framework for duty holders with no HSWA responsibilities to manage tree risk.

Duty holders with HSWA responsibilities

Duty holders with business interests active at their properties with obligations under the HSWA have a responsibility to take reasonable care to avoid acts or omissions that cause a reasonably foreseeable risk of harm. In practical terms, the process of assessing the risk and reacting to the findings can be shared between the duty holder and the tree inspector, as conceptualised in Figure 4.

The starting point is to assess site occupancy

Figure 3: The starting point is to assess site occupancy, which provides a reliable indication of whether people or property could be harmed if a tree fails. The assessment of the level of occupancy needed to trigger a check is a matter of judgement for each individual duty holder. If the occupancy is at the lower end of the occupancy spectrum, then no check is needed, and a future review must be scheduled. If the occupancy is at the higher end of the spectrum, the tree must be checked. If duty holders are not confident that they know what obvious defects are and can identify them, they should get help from a professional, and act on it. If they are confident in their abilities, they can check their own trees. If they see nothing of concern, then no immediate action is needed. If they discover a concern, they should get help from a professional and act on it. The risk from all trees should be regularly reviewed, irrespective of whether it is the duty holder or a professional that carries out the check.

Duty holders usually have knowledge of the level of occupancy of the land

Figure 4: Duty holders usually have knowledge of the level of occupancy of the land and there is no need for tree expertise to assess whether it is necessary to visit to check trees. The assessment of the level of occupancy needed to trigger a check is a matter of judgement for each individual duty holder. If the occupancy is at the lower end of the occupancy spectrum, it is unlikely to need any tree input and all that is necessary is to schedule in a future review. If the occupancy is at the higher end of the spectrum, then a check is needed, and there is an expectation that it is carried out by a person with enough experience and/or training to discover significant defects. This could be a trained arborist or an allied professional with specific training in recognising tree defects. If the check reveals no cause for concern, then no intervention is needed, and the next check is scheduled. If the check raises concerns, the need for intervention is assessed, and the duty holder is notified. If there is an imperative to keep the tree and the inspector is not sure about the implications of any discovered problems, or the extent of intervention needed, a more detailed inspection by a trained arborist can be advised. This is a much more detailed investigation than the check, and will clarify what intervention, if any, is notified to the duty holder. How duty holders react to this advice is for them to decide, based on their circumstances.

A conceptual tree risk spectrum

Figure 5: A conceptual tree risk spectrum, with the level of risk gradually increasing towards the highest extreme (red) and gradually decreasing towards the lowest extreme (green). There are no precise boundaries because the risk from trees cannot be reliably quantified, but the region where the risk from a particular tree sits can be described as towards one extreme or the other.

A bridge with a high volume of traffic (occupancy)

Figure 6: A bridge with a high volume of traffic (occupancy) would not normally be considered high risk location unless there was a high likelihood of failure. It’s the same for trees; high occupancy does not automatically mean high risk. (www.shutterstock.com)

A simplistic matrix conceptualising the outcomes of likelihood of failure and consequences combinations

Figure 7: A simplistic matrix conceptualising the outcomes of likelihood of failure and consequences combinations, reasoning that applies to both trees and locations. The level of risk is the product of these two components. A tree or location cannot be correctly called ‘high risk’ unless each component is also ‘high’, but a location can be called ‘high occupancy’ if lots of targets are present irrespective of the condition of the trees. NOTE: This conceptualisation builds on the generalisations illustrated in Figure 5 and must be viewed in the context of a spectrum, where ‘High’ and ‘Low’ represent the extremes, and ‘Medium’ is all that falls between.

Practical considerations for duty holders and arboricultural advisors

On a practical level, other important considerations for duty holders and arboricultural advisors designing tree checking regimes include the following.

Informal observations, formal checks and formal inspections

In a tree risk management context, there can be confusion over the differences between formal and informal tasks, and how they relate to checks and inspections. The Health and Safety Executive in its Sector Information Minute Management of the risk from falling trees or branches 9 usefully differentiates between checks, which are quick and visually oriented, and inspections, which are much more detailed and lengthy investigations. Both checks and inspections are formal tasks undertaken by trained operatives instructed to check specific trees within a specified timeframe. In contrast, informal observations are incidental to other activities and, while potentially helpful to supplement a formal risk management regime, they cannot be relied on in isolation as the main means of managing risks. Informal observations cannot replace the need for formal checks, and it seems unlikely that the courts would accept them as the principal tree-checking mechanism. Although the everyday use of terms such as ‘inspection’ and ‘check’ are interchangeable and have similar meanings, when it comes to tree risk management, they mean very different things, and arboriculturists would be wise to familiarise themselves with those subtleties.

Checking frequency

At first glance, the Cavanagh judgment and subsequent appeal would seem to suggest that a checking frequency of 18 months to two years is necessary to avoid liability, which is a significant increase for many duty holders and, if accepted, has the potential to substantially increase the cost of their regimes. However, it is relevant that the Court of Appeal was only looking at findings of fact relating to that situation in January 2012, namely a large and isolated lime tree in an area of high occupancy. Although this case will be a legal precedent, checking frequencies of three to five years for the wider tree population are likely to remain defensible if individual trees that may fall within the bounds of the judgment are identified for more frequent checking.4

However, ash trees now fall outside this general rule because of ash dieback disease, and all trees that could foreseeably cause harm must be treated differently to the wider tree population. It is a well-documented characteristic that once this species begins to decline in health, trees become vulnerable to secondary pathogens and can rapidly deteriorate to a condition of imminent failure. Evidence is still being evaluated on how quickly the disease can cause instability, but a checking frequency of every two years may be necessary once the disease has resulted in more than 50% defoliation. This is subject to ongoing evaluation by the Forestry Commission and arboriculturists should regularly check for updates to the standing advice.8

Risk spectrum

Conventional risk management theory originated in industrial conditions where reliable records allowed the level of risk to be clearly quantified, but that concept does not translate to trees very well. An alternative approach to understanding the level of risk is to conceptualise it as a spectrum with increasing risk in one direction and decreasing risk in the other (Figure 5). It is not possibly to reliably pinpoint the level of risk relating to trees, but it can be described as sitting towards one end or the other of the spectrum, and so can the direction of movement that arises when management interventions are carried out. The current mixed terminology for describing the level of risk can still be retained, with high, unacceptable and significant equating to one obvious extreme, and low, acceptable and insignificant equating to the other extreme. For example, a large tree with significant defects at a busy location could be described as sitting at the higher end of the risk spectrum and the intention of management interventions would be to shift it towards the lower end of the spectrum. Arboriculturists that struggle with the numerical approach to managing tree risk may find this a useful alternative.

The importance of basic and refresher training

Arboriculture is rapidly evolving because of improved technology, accumulating practical experience informing best practice, and the increasing number of legal developments relating to trees. This pace of change means that, in addition to routine basic training, regular refresher training is becoming essential to update professionals on the latest developments. More specifically, two PFD reports have highlighted deficiencies in training for recognising tree hazards when checking highway trees. In 2019, the National Training Organisation for the Land Based Industries (LANTRA) began offering a one-day training course called ‘Highway Tree Inspection’,10 which clarifies that when driven checks are carried out, the vehicle must be driven at low speed by a driver and a separate spotter must be looking at trees; the spotter must only look at trees and must not be attempting to assess highway and tree issues at the same time; and, where significant trees are present on both sides of the road, each side should be driven separately, and spotters should not attempt to look at both sides of the road during one pass. Furthermore, the vehicle must be prepared to stop to allow a closer visual check for obvious safety conditions and other triggers of possible threats to the highway. Formalised costeffective basic and refresher training has been available from LANTRA for nearly two decades now, and so corporate duty holders should expect the courts to take a dim view of inadequate training for staff charged with checking trees for hazard.

High risk and high occupancy

The Cavanagh first instance judgment and following appeal highlighted the need for care with the use of language relating to the terms ‘high occupancy’ and ‘high risk’ when it applies to trees and their locations.11 These terms are broadly interchangeable with a similar meaning in everyday conversational use, but in a technical context relating specifically to tree risk, they are worlds apart and mean very different things. This subtlety originates from the widely accepted definition that risk is the product of the likelihood of something bad happening and the consequences of that event (harm to people, property, or prospects), often summarised as Risk = Likelihood x Consequences. Figure 6 illustrates this concept where the risk of harm from using a busy bridge with constant heavy traffic is the product of the Likelihood of a structural failure and the severity of the harm that could arise (Consequences). In a tree context, the severity of the Consequences is often broken down into two components: 1) the occupancy, i.e., the number of targets; and 2) the amount of harm that could arise using the proxy of the size of the part expected to fail, on the assumption that the larger the part, the greater the harm is likely to be. For example, the level of risk from the ash tree in Figure 2 from its deteriorating condition as time passes could be described as moving towards the upper end of the risk spectrum shown in Figure 5 because the Likelihood of failure is high, and so are the Consequences, i.e., it is big (size) and there are many targets (occupancy).

In casual conversation, it is common for locations with lots of targets such as busy roads or property to be described as high risk, but that only considers the Consequences part of the equation in isolation without considering the Likelihood component. Just having lots of targets is not enough to make it ‘high risk’; there has to be a high likelihood of failure before it can be correctly called ‘high risk’. For example, the bridge in Figure 6 could reasonably be described as high occupancy, but it would not normally be thought of as high risk. It can only be high risk if there is a high likelihood of failure, and under a normal management regime, regular checks confine that likelihood to the lower end of the spectrum. It is the same for trees: there can only be a high risk if there is a high likelihood of failure, which can normally be controlled by regularly checking, and a high severity of consequences, i.e., big size and high occupancy (Figure 7). Whether it is bridges or trees, in the absence of a known high likelihood of failure, the correct description of a location with lots of targets is ‘high occupancy’, not ‘high risk’.

In summary, if a failure that causes harm results in legal proceedings, it is likely that duty holders and their arboricultural advisors will be expected to have considered all these matters, updated their risk management processes to account for them, and taken reasonable and proportionate measures to reduce significant risks of harm.

References

1. Decision-making for arborists: How to get it right and sleep tight on windy nights (2013). ISA Arborist News. html5.dcatalog.com/?docid=2e673a77-9270-4a84-b4d5-a2a400bb6926&page=52.

2. The implications of recent English legal judgments, inquest verdicts, and ash dieback disease for the defensibility of tree risk management regimes (2021). Arboricultural Journal. www.tandfonline.com/doi/full/10.1080/03071375.2020.1854996?src=.

3. Cavanagh -v- Witley Parish Council & Shepherd (2017). Ministry of Justice. www.barrelltreecare.co.uk/assets/Uploads/Cavanagh-judgment-no-markup.pdf. 4. Witley Parish Council -v- Cavanagh (2018). Ministry of Justice, Court of Appeal. www.bailii.org/ew/cases/EWCA/Civ/2018/2232.html.

5. Council fined following fatality caused by a tree branch striking a moving vehicle (2020). Health & Safety Executive. press.hse.gov.uk/2020/07/20/councilfined-following-fatality-caused-by-atree-branch-striking-a-moving-vehicle/.

6. Prevention of Future Deaths Report – Michael Arthur Warren (2014). Ministry of Justice. www.judiciary.uk/publications/michael-warren/.

7. Prevention of Future Deaths Report – Lucia Jayne Stear (2019). Ministry of Justice (www.judiciary.uk/publications/lucia-stear/).

8. Operations Note 46a: The management of individual ash trees affected by ash dieback (2019). Forestry Commission. www.gov.uk/government/publications/managing-ashtrees-affected-by-ash-dieback-operationsnote-46a/managing-ash-trees-affectedby-ash-dieback-operations-note-46a.

9. Management of the risk from falling trees or branches (2013). Health & Safety Executive. www.hse.gov.uk/foi/internalops/sims/ag_food/010705.htm.

10. Highway Tree Inspection (2019). LANTRA. www.lantra.co.uk/course/highway-tree-inspection.

11. Briefing note on Witley Parish Council -v- Cavanagh (2019). Barrell Tree Consultancy. www.barrelltreecare.co.uk/assets/Uploads/BTC136-Cavanagh-Briefing-Note-260119-Updated-031019.pdf.


Jeremy Barrell

Jeremy Barrell is an author and Managing Director of Barrell Tree Consultancy (www.barrelltreecare.co.uk/). He is an accomplished expert witness, appearing in seven of the 12 English civil judgments published in the last 20 years relating to harm arising from tree failures. He specialises in writing tree risk management policies for corporate and local authority duty holders responsible for large numbers of trees. Keep up to date with his posts on the latest developments in tree risk management at twitter.com/JeremyDBarrell.


This article was taken from Issue 193 Summer 2021 of the ARB Magazine, which is available to view free to members by simply logging in to the website and viewing your profile area.