All you need to know about tree surveys

What is a tree survey?

It is a tree report undertaken by a qualified arboriculturist of a tree, or group of trees, to assess their physiological and structural condition. Such details help a tree owner, developer, landscape designer, architect or property manager to make an informed decision over retaining or removing a tree or group of trees. The tree survey will give information including the species of tree, its measurements, age, health and life expectancy alongside recommendations regarding future management.

Is a tree survey necessary when making a planning application?

If you are thinking of building, adding an extension or renovating a property, trees must be considered if they are on your development site or close to it. A tree survey is relevant for developers, architects, site owners, landscape designers or project managers.

Local authorities in the UK are required to check the impact of any planning scheme on trees present and vegetation in close proximity to the proposed site.

A tree survey assesses the condition of tree stock to reduce risks.

Why are trees given such consideration?

Trees have a host of attributes: they benefit the environment and help maintain eco systems, they can have cultural and historical significance and provide a home to a wealth of species. Trees also add amenity value to a site or area, they can help reduce flooding in `at risk’ areas and improve air quality by producing oxygen and absorbing carbon dioxide.

Protection is given to trees under the Town and Country Planning Act 1990 and the Planning (Listed Buildings and Conservation Areas) Act 1990; these protect trees via Tree Preservation Orders and through conservation area designations.

Other relevant legislation is The Wildlife and Countryside Act 1981 which protects habitats and specific animal species. All local planning authorities will require documentation to clarify the potential impact of any development on trees.

Protected trees such as this ancient oak are likely to need a tree survey.

What are the different types of tree survey?

The BS5837: (2012) Tree Survey (or Stage One survey).

This is required to assess whether any trees need to be protected on or adjacent to a development site. It will be carried out by a qualified arboriculturist who will ask about your scheme, obtain details of the location and request a site plan before visiting the site and carrying out the survey.

The aim of the BS5837 Tree Survey is to inform you, the landscape designer and the local planning authority, about any issues or constraints to development with the site from trees above and below ground and enable an informed decision.

Using professional survey and GIS equipment including a Trimble handheld (Global Positioning System) location device and a PT Mapper Pro, which stores data about individual trees along with spatial information, the consultant will plot trees onto your Ordnance Survey tile or topographical survey.  

A tree constraints plan is produced which helps inform where development can proceed without negatively impacting on trees. It indicates the trees’ position, crown spread, retention category, shade constraints and root protection area, and can be overlaid onto your plans and drawings.

The detailed information gathered includes identification of the tree species, physical measurements of trees, overall health, predicted lifespan, future growth potential and recommendations about management.

Such high quality tree reports may help landscape designers decide which trees to incorporate into their design; they also identify any dangerous trees which may need to be removed for safety reasons. The professional tree surveyor assesses all trees on the site and considers their location in relation to the proposed planning application.

If conflicts are identified, the consultant investigates opportunities for revising the project to avoid harming the desirable trees in question. If this is not achievable, the trees’ quality assessment can be used to make an informed decision regarding the treatment of the tree in question: this may involve relocation, removal or replacement.  All trees on and adjacent to the site will also be recorded so that any designs can ensure the continued longevity of third-party trees.

Trees on a building site.

Category A.

This is the highest classification, given to the most important trees which are in good health and may have relevant environmental and cultural qualities or provide ecosystem services. Such trees are expected to live for over 40 years. Generally, a local planning authority will not give consent to carrying out work above or below ground within a certain distance of Category A trees unless there are exceptional mitigating circumstances.

Category B.

Here, trees have an expected lifespan of at least 20 years. For example, an avenue of mature lime trees in a town centre may fall into this category – while none are individually important enough to be classed as Category A, they are relevant to the urban landscape. A local planning authority will usually want such trees preserved; building within the root protection areas will require negotiation but there may be extenuating circumstances and innovative engineering techniques may come into play. If removal is required, compensatory planting may be required.

Category C.

Small trees (less than 150mm diameter) and trees in poor condition and not generally considered to pose a problem when planning permission is sought will be classed as Category C; they will have at least 10-years of life ahead of them. It is rare for them to be a constraint to development; however, a planning authority may require compensatory planting if they are removed.

Category U.

Trees which are dead or dying and may pose a safety risk will fall into this category; they have a lifespan of less than 10 years left and are not a constraint to development. They may also be in perfect health but causing a legal nuisance.

Highly visible tree roots.

Root Protection Area (RPA)

The tree condition survey must assess the impact that any development could have on underground elements of the tree: the rooting environment. The RPA is a notionally circular area around each tree that should remain undisturbed by development to ensure the future longevity of that tree.

The RPA is determined by multiplying the tree diameter of the stem at 1.5m above ground by 12. This establishes the radius of the RPA, and it can be used to decide what area to avoid during the development. Most tree roots are contained in the top 600mm to 800mm of soil; they are sensitive to soil compaction and need oxygen and gaseous exchange between the rooting medium and the atmosphere to take place in order to survive.

If a scheme involves the RPA, further investigations may be required to determine the position and size of any roots within a proposed footprint. To help in identifying exactly where roots lie beneath the soil, it can be useful to use the air spading technique; this involves tree surveyors directing a high-pressure jet of air at the ground to create a trench near the tree in question, revealing its roots without damaging them.

This method can inform the design and positioning of `in ground’ elements of a proposal and make a development scheme viable; it may of course confirm the original tree constraints, but the developer will not be in a worse position for having explored the option.

A tree survey under way in woodland.

Other types of tree survey include:

An Arboricultural Impact Assessment (AIA)

This follows from the BS5837 Tree Survey and is carried out to assess how a development will impact on existing trees. It is also important to consider potential impacts to the liveability of a proposal from any retained trees. The AIA identifies potential concerns and provides design guidance and/or solutions to maximise planning chances.

The tree report considers:

  • The interplay of proposed structures upon RPAs of trees that are desirable for retention, as these must be protected to ensure tree longevity post completion. Guidance is given to the design team as to how any such issues may be overcome.
  • The positioning and extent of new hard surfaces within and adjacent to RPAs and how these may be successfully achieved. Creating hard surfaces within the RPAs of trees is perfectly achievable if implemented in sympathetic ways.
  • Any planned level changes may impact RPAs and must be identified at this stage so that the issue may be rectified before the planning authority has a chance to refuse on these grounds.
  • Potential for seasonal nuisance from retained trees. Objections to planning applications often cite ‘future pressures for removal or pruning’ resulting from perceived potential issues of leaf and debris fall, shading and proximity. There is nuance here as different species have different attributes. Future growth is also considered.
  • Which trees will need to be removed or pruned to implement the proposal.
  • Mitigation planting for any tree losses or indeed to improve the current tree-related benefits.

The tree constraints plan drawing is combined with the architect’s proposed scheme to produce the AIA; the tree surveyor can then advise on scheme alterations and provide engineering solutions to deal with conflicts and help a plan progress.

A tree survey being carried out.

Arboricultural Method Statement

Once a defensible scheme is achieved and the proposals are finalised, this may be required by the local authority prior to it discharging planning conditions to ensure that contractors involved in construction activities from demolition, ground works, materials storage, vehicular movements and landscaping do not inadvertently damage trees by inappropriate actions. It will detail any specialist methodologies for installation of specific elements of the proposal that have potential to harm retained trees.

A Tree Protection Plan drawing will accompany the statement and will identify where protective measures are needed to prevent tree damage. This is a continuation of the AIA process and formalises solutions that have been incorporated into the design as a result of the advice given. This is the document that will form part of the planning permission. It must, by nature, be pragmatic and implementable on a work site.

Arboricultural supervision and site monitoring

As part of the planning process, a local authority may require inspection of measures to protect trees on development sites by way of regular monitoring and reporting. If any of the protective measures are identified as not being adhered to, or ineffective, the retained arboricultural consultant will propose solutions. An AIA is needed, plus a method statement and tree protection plan.

Mortgage Tree Report

Anyone who plans to buy land with trees on may need a tree report to satisfy a mortgage provider, who will assess how trees may affect the purchase. The report carries out checks for tree safety aspects and tree condition. A landowner may also require this report to present to an insurer. A tree survey report may be required by anyone buying or selling a house to investigate matters such as subsidence or tree problems and advise on how to reduce risks to an acceptable level.

Tree surveys are required to reduce risks on tree-lined roads.

Health & Safety Tree Survey

Private or commercial clients may require this survey to monitor single trees for risk hazard: regular surveys may be required to help tree owners or managers meet legal obligations on trees and mitigate risk posed by trees to people or property. Part of this survey work may involve ensuring that correct procedure is adhered to regarding Tree Preservation Orders (TPOs), which protect trees from removal or damage by pruning, or when dealing with trees in designated conservation areas.

Consultants can grade each tree to assess life expectancy and address issues such as fungal decay to enable informed decisions and reduce risk. Veteran and ancient trees may need to be surveyed for their habitat value and for population number recording reasons; typical issues to look out for include trunk hollowing which may occur in the ancient stage of a tree’s life – often the longest phase – as the tree becomes gradually colonised by fungi which can lead to rot and loss of limbs.

How to get a tree survey

To start a tree survey, you need to contact a suitably qualified ecological consultancy like Arbtech. They will be able to tell you what is required and when the survey will be done. Getting in touch with an ecological consultancy early on is recommended so that you reduce the chances of delaying your project. Here are the current costs for tree surveys carried out by Arbtech Consulting Ltd.

Stage 1: BS5837 tree survey and tree constraints plan: from £349. This is required for most planning applications where trees are on or adjacent to the proposed site. The only variable is the number of trees on the site; with a site containing 100 trees or less, prices start at £349 plus VAT.

Stage 2: ArboriculturalImpact Assessment, Method Statement and Tree Protection Plan: from £249.

Stage 3: Arboricultural Supervision and Site Monitoring: from £299. An Impact Assessment, Method Statement and Tree Protection Plan are needed before this survey can be carried out.

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