Trees: hazard assessments and condition surveys

The Thomson Ecology arboricultural team undertake tree management and maintenance. We provide inspections of any quantity of trees, from single specimens to large populations numbering thousands of trees. We provide detailed written reports and accurate mapping using GPS positioning. We also undertake internal decay detection and climbing surveys where a need is identified.

Legal obligations

Landowners have legal obligations under the Occupier’s Liability Act (1957 and 1984) and the Health and Safety at Work Act (1974) to ensure the safety of any visitors to their land, be they invited or otherwise. A Common Law duty of care is also owed to persons and structures on adjacent land. In both cases, it must be shown that reasonable measures have been taken to ensure that persons and structures are reasonably safe. The only legally acceptable way to achieve this with regard to trees is by regularly scheduled and recorded inspections.

Visual Tree Assessment

Visual Tree Assessment (VTA) is the industry standard for tree inspection. Our team employs this technique for all inspections and surveys, and works to all current industry best practice guidelines.

Assessing risk

The concept of risk depends on three main factors—likelihood of failure, target, and potential for damage. For instance, a tree with a large, detached hanging limb in the middle of a private woodland would not have a high level of risk due to a lack of target; however even a small tree with root plate heave next to a busy highway would pose a significant risk due to the high likelihood of vehicle impact should failure occur. Accurately assessing risk is therefore essential in a reasoned and appropriate approach to tree management. Our team uses systems such at THREATS and QTRA to ensure high levels of defensibility.

Types of inspections and surveys

Depending on the size of the tree population involved, different levels or types of inspection are deemed to fulfil the ‘reasonable’ criteria. Examples of inspection types include:

individual tree reports

low volume condition surveys

high volume rolling surveys for large landowners, such as local authorities

drive-by surveys for dense populations of roadside trees

Decay detection

If a defect such as a cavity is found during a tree inspection, it may be necessary to quantify the risk that the defect presents. This can be achieved by various methods of decay detection, such as the Resistograph microdrill. A Resistograph determines the resistance given to a calibrated drill as it travels through the stem or major limb of a tree. Cavities and areas of decay have a lower resistance, which is reflected on the drill’s graphical output. We are experienced in this and other forms of quantitative decay detection.

Honey fungus (Armillaria melea) attacking a purple plum ......................... Major fork on a Norway maple (Acer platanoides).