An arboricultural impact assessment, usually shortened to AIA, is the part of the BS5837:2012 process that works out how a proposed development would affect trees. It compares the development layout against the trees recorded on and around the site, identifies which trees would be removed and which retained, and assesses where construction would encroach on root protection areas. Councils commonly ask for one when a planning application involves a site with trees, either with the application itself or as a condition on the permission.
Where the AIA sits in the BS5837 process
BS5837:2012 is the survey standard for trees and development, and the AIA is one stage in a sequence. Each stage builds on the one before.
- Tree survey. Our surveyors record each relevant tree and grade it into one of the categories A, B, C or U set out in the standard.
- Tree constraints plan. The survey data is plotted on a plan, including the root protection area around each tree, so the designer can see where the trees limit what can be built.
- Arboricultural impact assessment. The proposed layout is set against those constraints. The AIA states which trees would be lost, which would be retained, and where the works would encroach on root protection areas.
- Arboricultural method statement and tree protection plan. Where the assessment identifies impacts, these documents set out how retained trees will be protected while the work is carried out.
Because the assessment depends on accurate survey data, a BS5837 tree survey comes first. An impact assessment written without one has nothing reliable to assess.
What the assessment covers
The AIA is a comparison between what stands on the site now and what is proposed. In practice it answers three questions.
Which trees would be removed?
The assessment lists the trees the design would require to be felled, along with their survey categories, so the council can weigh what would be lost against what is proposed.
How would retained trees be affected?
Removal is not the only impact. Where foundations, drives, services or site access would encroach on a retained tree’s root protection area, the AIA flags it, and the method statement then has to explain how that encroachment will be managed.
Are any of the trees protected?
Works to a tree covered by a Tree Preservation Order need council consent, and works to trees in a conservation area need six weeks written notice to the council. Penalties for unauthorised works on protected trees can include unlimited fines, so protection needs establishing early. Our free checker at /is-my-tree-protected/ reads the national planning dataset and gives an indicative answer, but the council holds the definitive register, so check with your council. This is general information, not legal advice.
How it relates to the method statement
The AIA and the arboricultural method statement do different jobs. The assessment identifies the effects of the proposal. The method statement sets out how the work will be carried out so that retained trees are protected, and the tree protection plan puts those measures on a drawing so everyone on site can see them. On most applications the documents travel together: the tree survey establishes what is there, the impact assessment establishes what the proposal would do to it, and the method statement and tree protection plan establish how the retained trees will come through construction unharmed.
When a council asks for one
Councils validate planning applications, and where trees stand on or next to a site, many will not consider an application complete without tree information. Sometimes the AIA is required when the application is submitted. Other times permission is granted with a condition requiring the tree documents before work starts. Practice varies between councils, so check with your council about what your application needs. If you have been asked for an arb report, a tree report or a BS5837 report as part of an application, an AIA is usually part of what is meant.
An independent assessment
Our surveys and impact assessments are priced and delivered on their own. The findings are what the trees need, and you are free to take the report to any contractor or use it however your application requires. If tree work does follow, we can also carry it out as an ARB Approved Contractor (AC2637). Great Oaks Tree Services Ltd is based at Freshfield Farm, Freckleton, Preston, holds Constructionline Gold accreditation and carries £1m professional indemnity insurance. Our qualified team carries out tree surveys across Preston, Lancashire and the North West. We quote within one working day, survey visits happen within days, not weeks, and the price we quote is the price you pay.
If you need an arboricultural impact assessment, tell us about the site using the free scope check form at our survey enquiry form, or call the office on 07884 274693 and one of our surveyors will talk it through with you.
