In 2010, we were engaged to conduct a tree risk assessment and provide recommendations for future management of 8 woodland sites. Management of risk from falling trees had previously been on an ad-hoc basis, with staff reacting to situations as they arose.
One of the sites is a 100-acre site attracting over 100,000 visitors each year. The site contains two major visitor attractions.
We met with the client to clarify their priorities, gleaning important information from their historical knowledge of the sites and the way in which they were accessed by the public. We advised a risk-based approach to the management of tree safety on the site using our Quantified Tree Risk Assessment method. First taking an overview of the trees and the land-use (people and property) upon which trees could fail, we considered the relationship between trees, infrastructure, site users, neighbours, and the public.
A walkover assessment of each site was carried out, viewing at an appropriate level of detail all trees within falling distance of highways, a railway, residential boundaries, footpaths and other areas of significant land use. Using our bespoke CWSurveys data collection software, the trees and woodlands were plotted on drawings. The grouping of trees on each site was informed by the structure of the tree population and how it interfaced with land-use (people and property). Trees were plotted individually only where they were identified as having potentially significant risks associated with them, or there was some other management reason to record them. More detailed assessments of tree stability were made if the initial view was insufficient for the surveyor to reach a conclusion.
The assessments have been subject to regular reviews and meetings with the client to discuss our findings. Over the years, we have been engaged on additional projects to evaluate the potential impacts of construction and other activities in and adjacent to the woodlands.
Significantly elevated risks considered to be unacceptable were mitigated. However, in line with current good practice (National Tree Safety Group, 2011) where risks were identified as being potentially tolerable, the benefits of retaining the hazard, e.g. the dead tree or damaged branch, were considered and balanced against the risk, and in many cases hazards were retained providing the risks were within tolerable limits.
For each site, the client was provided with a schedule of our inspection records in spreadsheet format, and tree and groups plotted on a drawing for each site. Using a colour-coded traffic light system to identify levels of risk, both on the drawings and in the schedules, enabled the client to identify risk distribution across the site at a glance. We provided our client with sufficient information to enable reasonable safety and silvicultural management of their tree resource. Rather than dictating to the client by specifying timescales for implementation of remedial and other management works, we categorised works in a way that enabled the tree manager to work within the budgetary and day-to-day management constraints that only they have knowledge of.
This approach provides clear guidance on the management of risk from falling trees and encourage a proactive approach to the silvicultural management of their tree populations. This will often in itself reduce the risks.
Cheshire Woodlands use of Quantified Tree Risk Assessment has proved invaluable. It has helped us to retain trees that were condemned by another advisor. They have used measurable data to provide us with a valid tree risk assessment.