What is QTRA?

The Quantified Tree Risk Assessment (QTRA) method, developed by Mike Ellison at Cheshire Woodlands, applies established and accepted risk management principles to tree safety management. The method moves the management of tree safety away from labelling trees as either ‘safe’ or ‘unsafe’ and in most situations away from requiring definitive judgements from either tree assessors or tree managers. Instead, QTRA quantifies the risk from tree failure in a way that enables tree managers to balance safety with tree value.
By quantifying the risk from tree failure, QTRA enables a tree owner or manager to manage the risk in accordance with widely applied and internationally recognised levels of risk tolerance. QTRA also provides a decision-making framework which allows decision-makers to consider the balance between the benefits provided by trees, levels of risk they pose, and costs of risk management.

How often do I need a tree inspection and risk assessment?

That depends on the characteristics of your trees and their location. If you follow the National Tree Safety Group guidance for domestic tree owners, and you have a population of healthy trees, it might be sufficient that you keep an eye on your trees, check them after storms for obvious defects such as splits, partial uprooting and broken branches, and then engage an arboriculturist when you identify something of concern that you’re not sure about.

What level of risk do trees pose?

How long is a piece of string? For the average person in the UK, the annual risk of dying as a result of being struck by a tree is around 1 in 10 million. To put that into some sort of perspective, the risk of death on our roads is almost 600 times greater at around 1 in 17,000 per annum. Of course, in that huge mix there is a wide range of risk and some trees do present very high risks, particularly when they are large and unstable, and adjacent to busy areas. But, importantly, most trees present very low risks.

What does a Tree inspection and risk assessment report include?

It depends on the level of detail that you are looking for and the characteristics of your tree population and location. Big old trees adjacent to busy areas require more detailed assessment than younger trees in a low use location. Sometimes we will carry out a detailed inspection of each tree, but more commonly we carry out a Walkover Assessment, taking a general view of your trees at an appropriate level of detail, we then record individually only those trees that present significantly elevated risks, or where there is some other reason to.

Who is responsible for tree safety?

Property owners and managers have a duty (under English law) to ensure, insofar as is reasonably practicable, that people and property are not exposed to unreasonable levels of risk from the mechanical failure of their trees. In 2007, The National Tree Safety Group was formed, and in 2011 it published a suite of guidance on taking a reasonable and proportionate approach to tree safety, which has been endorsed by the UK Health & Safety Executive. Take a look ( https://ntsgroup.org.uk/guidance-publications/), there’s simple, clear guidance for the domestic tree owner, and more extensive guidance for large landowners, councils, and tree professionals.

My neighbour’s trees are close to the site boundary, do these need to be included in a survey?

This depends on the extent of the size of the trees and whether their roots are likely to be significantly impacted by the proposal. We consider the Root Protection Area (RPA) of the tree, which is the area of ground around the tree that needs to remain undisturbed during construction operations. The RPA is initially represented by a circle that is centred on the tree stem and has a radius equal to 12 times the stem diameter measured at a height of 1.5m.

What is a BS5837 Survey and why do I need one?

The importance of trees within the planning system has increased significantly in recent years, and the effects of development upon trees is a ‘material consideration’ in the planning process. This means that local planning authorities must consider the impacts on trees when determining planning applications.
In practical terms, this means detailed arboricultural information must be submitted where trees are present on or adjacent to a site beginning with a tree survey to the standards set out in BS5837:2012 Trees in relation to design, demolition and construction – Recommendations as a pre-requisite for the registration of planning applications.