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Arboricultural consulting Tree surveys and assesments

Planning and development surveys (to BS5837)

When developing a site, it is important to consider trees early in the planning process. BS5837:2012 Trees in relation to design, demolition and construction - recommendations, gives national guidance on the correct procedures required to satisfy Local Planning Authorities. Full planning permission may then be subject to material conditions to protect trees on site before, during and after construction.

Arboricultural surveys and Tree Constraints Plan

Thomson Ecology specialises in carrying out high quality arboricultural surveys and producing site-specific arboricultural reports in line with BS5837:2012. Using hand-held GPS mappers, we accurately record the location of the trees onto a digital, topographical plan and measure a range of the trees’ attributes. We then assess their structural and physiological condition and identify any tree works required to mitigate against harm to people or property. As defined in BS5837:2012, each tree is categorised according to its qualitative and arboricultural, landscape or cultural and conservation value.

Included in our reports is a Tree Constraints Plan. This plots the locations, the canopy extents and the Root Protection Areas (RPA) for each recorded tree. The RPA is the minimum area around a tree that must be preserved in order to help maintain the future health and stability of the tree. The extent of the RPAs will help you to determine the space available for your proposed development plans.

Arboricultural Impact Assessment (AIA)

Once the detailed design for the site has been drawn up, an evaluation of the effect of the proposed development on the trees can be determined in an Arboricultural Impact Assessment (AIA). Frequently requested as part of a planning application, the AIA details the likely impact that the design will have on existing trees, including:

The AIA usually includes a draft Tree Protection Plan visually illustrating the tree protection and special construction measures required.

Arboricultural Method Statement (AMS) and Tree Protection Plan

Once the final design has been produced, we produce an Arboricultural Method Statement (AMS) which gives precise details of how retained trees will be protected during construction, and how works within the Root Protection Areas (RPAs) of retained trees will be undertaken without detriment to the future health of the trees. The AMS is usually drawn up once planning permission has been obtained and the construction phasing decided. However, local planning authorities can ask to see generic method statements at the planning submission stage.

Planning and development surveys (to BS5837)

Trees: site supervision

When prescribed by a planning condition or in an AMS, we undertake arboricultural site supervision of construction work close to trees to ensure that damage to trees is avoided. This often involves supervising and checking the erection of tree protection fencing and temporary ground protection, maintaining supervision during excavation works within the RPAs of retained trees and ensuring that installation techniques for new hard surfacing and specialist foundations are carried out without negatively affecting the retained trees.

Arboricultural site supervision leads to a clearly auditable system of site monitoring which gives clients confidence that their activities have not had a detrimental effect on the retained trees, and can be used to allay any concerns the Local Planning Authority may have over construction works.

Tree hazard assessments and tree condition surveys

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 carried out by suitably qualified persons.

Visual Tree Assessment

Visual Tree Assessment (VTA) is the industry standard and legally accepted method for tree inspections. It recognises symptoms produced by a tree in response to a weak spot or mechanical stress, and identifies other growth defects. Our team of arboricultural consultants employ this technique for all arboricultural surveys they undertake and use its findings when determining any tree works required.

Tree risk assessment

The concept of risk depends on three main factors – the likelihood of failure of all or part of the tree, the target which might be affected and the 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 as 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 tree inspection types include:

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 tree 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.