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When trees are present on or near a development site, they can shape everything from layout and foundation design to planning strategy and construction sequencing. The earlier those constraints are understood, the more options the project team has. Leave tree considerations too late and the design may already be committed to positions that are difficult, or expensive, to change.
An Arboricultural Impact Assessment is the document that brings tree constraints and proposed development into the same conversation. It explains how a scheme may affect existing trees, which can be retained, what may need to be removed and how retained trees should be protected through demolition and construction.
An Arboricultural Impact Assessment (commonly referred to as an AIA) is a report that assesses the likely effect of proposed development on existing trees. It is usually prepared as part of the BS5837 planning process, following an initial tree survey and Tree Constraints Plan, and tests the proposed layout against the tree information already collected.
In practical terms, it addresses questions such as:
Our BS5837 tree surveys are designed to support the full planning process, from initial survey data through to impact assessment, mitigation and practical protection measures.
An Arboricultural Impact Assessment should not be viewed in isolation. It is one part of a wider process that helps design teams and planners understand trees in relation to development. A typical sequence looks like this:
For development teams, the scope of BS5837 matters. Tree considerations do not end when the planning report is submitted; they carry through into the build phase as well.
An Arboricultural Impact Assessment is commonly required where a development site contains trees, sits close to trees, or may affect trees on neighbouring land. This can include:
A tree does not have to sit inside the red line boundary to be relevant. Trees on neighbouring land can still influence layout, access, foundations and construction methods if their crowns or root protection areas extend into the site.
This is one reason early advice matters. If the first proper tree review happens after the layout is fixed, the options narrow and the risk of redesign increases. Great Oaks provides tree reports for planning applications that set out constraints, impacts and protection measures clearly, so the information can be used effectively by architects, planners, engineers and contractors.
A good AIA should be clear enough for a planning officer to understand, but practical enough for a project team to use. The detail will depend on the scale and complexity of the scheme, but common sections include:
The result should be a report that serves the planning application and helps the project move from consent into delivery.
It is easy to think of an Arboricultural Impact Assessment purely as a planning document. Its real value, however, often comes earlier in the process.
An AIA commissioned before the layout is finalised can identify conflicts while there is still room to respond. It can show where a building footprint encroaches on a Root Protection Area, where an access route may need adjusting, or where a service trench would create avoidable risk. Identifying these issues before submission is considerably easier than addressing them through planning conditions or post-consent redesign.
The Planning Portal’s guidance on trees and planning permission notes that local rules can affect what permissions are needed. Where protected trees or trees in conservation areas are involved, the planning strategy needs to be confirmed before work starts. An AIA helps bring those issues into the design conversation early enough to be managed properly.
Tree protection can affect both design options and programme timing, and it should be checked before assuming a tree can be removed or altered.
Some trees are protected by Tree Preservation Orders. Others are protected by virtue of standing in a conservation area. In both cases, pruning, removal or other works may require consent or formal notice before they can proceed. GOV.UK guidance on Tree Preservation Orders and trees in conservation areas sets out how these protections operate in England.
An Arboricultural Impact Assessment can clarify the implications for the proposed scheme and support the planning submission by explaining whether tree works are necessary, proportionate and directly linked to the design. It should also demonstrate how retained protected trees will be safeguarded during demolition and construction.
Root Protection Areas are one of the most important considerations in the BS5837 process. The RPA is the area around a tree that should be protected to help safeguard its roots and rooting environment. Development activity within or close to this area can affect a tree’s long-term health and structural stability. This may be due to excavation, compaction, level changes, contamination, surfacing or service installation.
Development near trees is not necessarily impossible as a result, but the design team needs to understand the constraint and consider suitable approaches. Depending on the situation, a scheme might require revised building positions, adjusted access routes, no-dig surfacing, alternative service corridors, hand digging or supervised excavation, changes to drainage or levels, or root investigation to inform final design decisions.
Where root location needs more detailed evidence, our root investigation and tree radar surveys can help identify likely root presence, depth and direction, supporting more informed design decisions where roots and infrastructure meet.
Not all trees carry the same planning weight. Some are significant because of their size, age, condition, ecological value, historic associations or contribution to the wider landscape. These need to be identified early.
Ancient and veteran trees require particular care. Government guidance on ancient woodland, ancient trees and veteran trees is relevant wherever these features may be affected by development.
If a high-value tree is discovered late in the process, the consequences can be significant. The layout may need to change, further reports may be required and the planning risk increases. A well-timed AIA keeps those decisions visible before the project becomes locked into a design that is difficult to defend.
Where a tree has genuine landscape value but cannot remain in its current position, tree relocation may be worth exploring on suitable sites.
These three documents are often referenced together in planning conditions, but they do different jobs. Understanding the distinction helps project teams know what is expected at each stage.
Great Oaks has a separate guide to tree protection plans for development sites, which explains how protection measures can reduce redesigns, planning queries and construction-stage issues. For more complex sites, the planning authority will typically expect all three documents to work together.
Tree-related planning delays often stem from gaps that could have been addressed earlier. Common issues include:
These issues do not always prevent a scheme from proceeding, but they can generate questions, revisions and uncertainty that slow the programme. A clear AIA reduces that friction by demonstrating that tree impacts have been properly assessed and that the project team has a practical plan for managing them.
An Arboricultural Impact Assessment is not simply a document that lists tree removals. Used early enough in the design process, it can also identify where modest changes to layout, access or construction method would allow better trees to be retained.
Sometimes removal is unavoidable. A tree may be low quality, in poor condition or in direct conflict with an essential part of the scheme. In other cases, a revised building position, an alternative service route or a different construction approach can protect a valuable tree without compromising the development.
This is where arboricultural advice can add genuine value to the design process, helping teams understand which constraints are fixed, which can be engineered around and which call for a different approach altogether.
An Arboricultural Impact Assessment should make tree constraints clearer, not more complicated. It should help the planning team, the design team and the site team understand what needs to happen next, and give them the information to act on it.
Great Oaks provides BS5837 tree surveys, Arboricultural Impact Assessments, Tree Protection Plans, Arboricultural Method Statements and practical arboricultural consultancy across Preston, Lancashire and the wider North West.
Whether you are preparing a planning application, responding to planning comments or reviewing a development layout before submission, contact Great Oaks to discuss your site.
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