Arboricultural Impact Assessment in Bromley

An arboricultural impact assessment — usually shortened to AIA — is a specialist report, written by a qualified arboriculturist, that assesses how a proposed development will affect the trees on and around a site, and how those trees affect the development in return. It is the analytical heart of a family of tree documents prepared to British Standard BS5837:2012, 'Trees in relation to design, demolition and construction'. Its purpose is to give the local planning authority everything it needs to judge whether a scheme strikes an acceptable balance between building and trees, and to condition how the retained trees are protected if permission is granted.

The AIA does not stand alone. It sits on top of a BS5837 tree survey, which records and categorises every tree of relevance to the site, and it is accompanied by a tree constraints plan that maps those trees and their root protection areas. Where trees are to be retained close to construction, the AIA leads on to an arboricultural method statement and a tree protection plan, which set out exactly how the retained trees will be safeguarded during demolition and building. Together these documents are what most people, and most councils, mean when they talk loosely about 'a BS5837 report' or 'a tree survey for planning'.

What makes the AIA distinct from the survey underneath it is that it is a judgement, not just a record. The survey says what is there and how good it is; the AIA says what your specific design does to it — which trees are lost, which are retained, where the layout encroaches on root protection areas, what pruning is needed, whether new buildings will overshadow trees or trees overshadow buildings, and whether the remaining relationship between the trees and the homes is a sustainable one for the long term. That is the question the council actually has to answer, and the AIA is written to answer it directly.

So when we talk about an arboricultural impact assessment for a Bromley project, we mean a properly sequenced package: an accurate BS5837 survey of every relevant tree; a tree constraints plan that puts those trees and their root protection areas onto the site layout; an impact assessment that tests the proposed design against them; and a tree protection plan and method statement that show how the retained trees survive the build. The rest of this page explains how each part is prepared, and why it matters so much in this particular, tree-rich borough.

The short answer, in Bromley, is: far more often than owners expect. As a rule of thumb, if there are trees on your site, on immediately neighbouring land, or on the highway close enough that their roots or canopies could be affected by what you are building, you should assume the council will want a BS5837 tree survey and an arboricultural impact assessment. Bromley's Local Plan is explicit that where development proposals threaten to affect important or significant trees, the council will require a tree survey and arboricultural implications assessment prepared in accordance with BS5837:2012. In practice that catches a very large proportion of residential applications in this borough.

The requirement is driven by the local validation checklist. When you submit a planning application, Bromley checks it against a list of documents that must accompany applications of that type in that location; if a required document is missing, the application is not validated and is not assessed until the gap is filled. An AIA and tree survey is one of the documents Bromley will request where trees could be affected, so a missing or inadequate tree assessment is a classic cause of an application being held at validation — losing you weeks before the case is even looked at on its merits.

Certain situations make an AIA close to unavoidable. Any protected tree — one covered by a Tree Preservation Order, of which Bromley has over two thousand — near a development almost always triggers the requirement, as does any tree within one of the borough's forty-seven conservation areas, where trees are protected by law whether or not there is a specific Order. New dwellings, backland and garden-plot development, knock-down-and-rebuild schemes, basements, and extensions close to trees are the usual candidates. Even a modest extension can need one if it sits within the root protection area of a decent tree next door.

The safest approach in Bromley is to treat the tree question as one of the first things to settle, not one of the last. We check, at feasibility, what trees are on and around the site, whether any are protected, and whether the proposal is likely to affect them — and therefore whether an AIA will be needed and what it will have to show. That early check does two things: it tells you whether you need the report at all, and, far more importantly, it lets the trees shape the design before you have committed to a layout that the trees will later veto.

The document that governs almost every aspect of tree assessment for planning in England is British Standard BS5837:2012, 'Trees in relation to design, demolition and construction — Recommendations'. It is the reference point councils use, the framework Bromley's own Local Plan names, and the standard a competent arboriculturist works to. It sets out how trees should be surveyed, how they should be categorised for their quality and suitability for retention, how root protection areas are calculated, and how trees should be protected during construction. When Bromley asks for a 'BS5837 report' or a 'tree survey to BS5837', this is what it means.

The standard is deliberately sequential, and understanding that sequence is the key to understanding the whole process. First comes the tree survey, which records and categorises the trees. From the survey flows the tree constraints plan, which shows the trees, their crown spreads and their root protection areas on the site layout so that constraints are visible before the design is fixed. The design is then developed with those constraints in mind. The arboricultural impact assessment tests the resulting proposal against the trees, and finally the arboricultural method statement and tree protection plan set out how the retained trees will be protected on site.

The philosophy behind BS5837 matters as much as its mechanics. The standard is built on the principle that trees should be a material design consideration from the outset, not an obstacle to be dealt with once the building has been drawn. It expects the designer to understand the trees, to design around the ones worth keeping, and to justify any losses — rather than to design in a vacuum and then squeeze the trees to fit. This is exactly why we bring the tree survey forward to the start of a project: BS5837 is written on the assumption that you will design with the trees, and schemes that ignore that assumption are the ones that come unstuck.

BS5837 is a British Standard, not a statute, so it is not law in the way a Tree Preservation Order is. But it has enormous practical force: it is the recognised methodology, it is what Bromley expects, and an assessment that does not follow it properly will be given little weight and may be rejected. In effect, following BS5837 is the price of being taken seriously on trees in a Bromley application — which is why every part of the package we prepare is built around it.

Every arboricultural impact assessment starts with a tree survey, carried out on site by a qualified arboriculturist. The surveyor visits the site and records data on every tree — and every significant hedge and group of trees — within influencing distance of the proposed works, including trees on neighbouring land and on the highway where they could be affected or could affect the scheme. For each tree the survey records its species, its height, its stem diameter (measured at 1.5 metres above ground level), its crown spread in the cardinal directions, its crown clearance above ground, its estimated age class, its physiological and structural condition, and any defects, disease or management needs.

From those measurements the surveyor assigns each tree a retention category using the BS5837 cascade chart. Category A trees are the highest quality, with an estimated remaining life expectancy of at least forty years — trees that make a real contribution and should strongly influence the design. Category B trees are of moderate quality, with a remaining life of at least twenty years. Category C trees are of low quality — often small, young or unremarkable — with a remaining life of at least ten years, or trees whose value is limited. Category U trees are those in such poor condition, or so dangerous, that they cannot realistically be retained for more than around ten years and are recommended for removal irrespective of the development.

That categorisation is the single most consequential output of the survey, because it drives everything that follows. It tells the designer which trees are worth designing around and which matter less; it frames how the council will view any losses (removing a category A tree is a serious matter; removing a category U tree usually is not); and it feeds directly into the impact assessment. A survey that categorises trees carelessly — over-grading mediocre trees, or under-grading good ones to make a scheme look better — produces an assessment that the council will not trust, so honest, defensible categorisation is fundamental.

The survey is presented as a schedule — a table of every tree with its data and category — accompanied by the tree constraints plan. In a borough as wooded as Bromley, that schedule is often long: a single suburban plot in the leafy north can have mature trees on every boundary and in every neighbouring garden, and a plot on the edge of the North Downs can back onto ancient woodland. The survey has to capture all of it accurately, because the impact assessment can only be as good as the survey it rests on.

The most important constraint a tree imposes on a design is usually invisible, because it is underground. The root protection area, or RPA, is the notional area around a tree that must be left undisturbed to sustain the tree's health and stability. BS5837 defines it as the minimum area around a tree deemed sufficient for its continued survival, and it is what the design has to respect: build, dig, compact soil, store materials or run services within an RPA and you risk killing or destabilising the tree, often slowly and after the building is finished.

BS5837 gives a simple formula for calculating the RPA. For a single-stemmed tree, the RPA is a circle with a radius of twelve times the tree's stem diameter (measured at 1.5 metres above ground level). A tree with a 30-centimetre stem, for example, has an RPA radius of 3.6 metres; a large mature tree with a 60-centimetre stem has an RPA radius of 7.2 metres — a substantial circle. The calculated area is capped at 707 square metres, equivalent to a radius of about 15 metres, so even the very largest trees have a defined limit. For multi-stemmed trees there are variations on the calculation, and the shape of the RPA can be adjusted where local soil and rooting conditions justify it, but the twelve-times-diameter rule is the starting point.

The RPA is plotted onto the tree constraints plan as a circle (or an adjusted shape) around each retained tree, and it becomes a no-go zone for the design. This is where trees really bite on a scheme: a mature oak or beech on a Bromley boundary can throw an RPA that reaches well into the buildable part of a plot, and the RPAs of several trees together can leave surprisingly little developable ground. Understanding the RPAs before the layout is drawn is the difference between a design that works with the trees and one that has to be torn up when the arboriculturist points out that the proposed extension sits squarely on top of a protected tree's roots.

Where a design must place hard surfacing, a path or occasionally a structure within an RPA, BS5837 allows for special engineering solutions — no-dig construction, cellular confinement systems, pile-and-beam foundations, ground protection — that can permit limited works without unacceptable harm to the roots. These are legitimate and often decisive tools on tight Bromley plots, but they have to be designed and justified in the AIA and method statement, not simply asserted. Getting the RPA right, and being honest about any incursion into it, is at the very heart of a credible arboricultural impact assessment.

The tree constraints plan (TCP) is the drawing that turns the survey into something a designer can work with. It takes every surveyed tree and plots it accurately onto the site layout — showing the trunk position, the crown spread, the root protection area, the tree's category (usually colour-coded, with category A, B, C and U shown differently), and any above-ground constraints such as shading arcs where trees will cast shadow onto a proposed building. It is, in effect, a map of where you can and cannot build.

The order in which the TCP is produced is the whole point. BS5837 expects the constraints plan to come before the design is fixed, so that the layout responds to the trees rather than colliding with them. On a Bromley plot that means we produce the survey and the constraints plan early, and design the proposed scheme on top of it: keeping the footprint clear of the RPAs of the good trees, placing the building where it does the least harm, arranging windows and gardens to work with the canopies, and taking any unavoidable losses from the least valuable trees. Design led by the constraints plan is what BS5837 is really asking for.

The shading arcs on a TCP are a subtlety that catches many schemes out in a leafy borough. A large tree to the south of a proposed house can overshadow it heavily, and while trees generally win that contest in planning terms, a scheme that puts habitable rooms and gardens in permanent deep shade is a poor scheme — and a future occupier who wants the tree removed for light is a future enforcement problem. Designing so that the home has reasonable light without needing the tree gone is part of a good relationship between building and tree, and the TCP is where that is worked out.

The constraints plan also becomes the foundation for the two drawings that follow: the impact assessment's analysis of what the design does to each constraint, and the tree protection plan that shows how the retained trees will be fenced and protected. Because all three drawings share the same accurately plotted trees and RPAs, the whole package is internally consistent — the trees shown as retained on the design are the trees protected on the protection plan, and the RPAs respected in the layout are the RPAs fenced on site. That consistency is exactly what a Bromley tree officer looks for.

With the survey done and the design developed against the constraints plan, the arboricultural impact assessment analyses the specific effect of the proposal on the trees. This is the analytical core of the whole exercise, and it is where the arboriculturist's judgement earns its place. The AIA identifies which trees are to be removed and why; which are to be retained; where the proposed works encroach on root protection areas and by how much; what pruning or crown work is needed to accommodate the scheme; and whether new structures will overshadow trees or trees will unduly overshadow new homes.

For each retained tree, the AIA assesses the impact both above and below ground. Above ground it looks at the proximity of buildings to canopies, the pruning required, the effect of level changes, and the pressure a new occupier might put on the tree for light or leaf-fall reasons. Below ground it assesses incursion into the RPA — from foundations, excavations, services, drainage, hard surfacing, compaction and material storage — because that is where most tree damage from construction actually happens. The assessment then judges whether, taken together, the impacts are acceptable and the retained trees can be expected to survive in good health for the long term.

Where trees are to be lost, the AIA has to justify it and, usually, propose mitigation. Removing a category U or a poor category C tree is generally straightforward to justify. Removing a category A or good category B tree is a serious matter that the council will scrutinise hard, and in Bromley — where trees carry great weight and many are protected — an unjustified loss of a good tree is often fatal to an application. The AIA sets out the arboricultural case for any removal, and typically proposes replacement planting, because the mandatory and policy expectations now running through the system lean strongly towards net tree gain, not loss.

Crucially, the AIA is written to inform a planning decision, so it does not simply describe impacts — it reaches conclusions the council can rely on. It states clearly whether the scheme is arboriculturally acceptable, on what basis, and subject to what protection and mitigation. A good AIA gives the tree officer a clear, evidenced recommendation to agree with; a weak one leaves the officer to work out the answer themselves, which in a tree-sensitive borough usually means a refusal or a demand for more information. Writing the AIA to close the question, honestly, is the skill of it.

An assessment that concludes trees can be retained is only credible if it also shows how they will actually survive the build — and that is the job of the tree protection plan (TPP) and the arboricultural method statement (AMS). Most tree damage on a construction site happens not through deliberate felling but through carelessness: roots severed by a trench for a drain, soil compacted by a lorry parked over an RPA, bark stripped by a passing digger, or the ground within an RPA quietly used for storing bricks and mixing concrete. The TPP and AMS exist to prevent exactly that.

The tree protection plan is a drawing showing the physical protection measures on site: the location of protective barriers (usually a robust fence to a defined specification, positioned at the edge of the RPA to create a construction exclusion zone), any areas of ground protection where limited access within an RPA is unavoidable, and the trees being retained and removed. It defines, in effect, a fortress around the roots of the retained trees, into which construction traffic, materials and excavation may not go without specific, controlled measures.

The arboricultural method statement is the written companion to that drawing. It sets out, in practical detail, how the retained trees will be protected through each phase of demolition and construction: how and when the protective fencing is installed and that it stays up throughout; how any works that must happen within an RPA (a service run, a section of hard surfacing) are carried out using special foundations, hand-digging or no-dig techniques; how materials and machinery are kept clear of the RPAs; how any approved pruning is specified (referencing BS3998, the standard for tree work); and, on sensitive sites, arrangements for arboricultural supervision of key operations with named contacts.

In Bromley, the TPP and AMS are frequently secured by planning condition, meaning permission is granted subject to the protection measures being provided and followed. That has teeth: breaching the condition can invalidate the permission and, where protected trees are involved, expose you to prosecution. So these are not paperwork for the file — they are the practical instructions that keep the trees alive and keep the development lawful. We prepare them to be genuinely usable on site, so the contractor knows exactly what is required and the retained trees the whole application relied on actually make it through the build.

Bromley wears its greenery as an identity. It is the largest of the London boroughs by area, the most rural, and by common measure the most heavily wooded — with around 2,181 hectares of woodland, of which the council itself owns some 552 hectares, and a tree canopy that is among the most extensive in the capital. Until 1965 it was part of Kent, and much of its southern half still reads as Kent countryside: farms, hedgerows, chalk downland and, above all, woods. The borough was created in 1965 from a group of former Kentish authorities, and it has protected its trees and its landscape with unusual determination ever since.

The borough's northern half is the classic 'leafy suburb' — the mature Victorian and Edwardian villas of Beckenham, Chislehurst, Shortlands, Bickley and Bromley itself, set in generous gardens lined with the plane, lime, oak, beech, cedar and pine that give the streets their character. These suburban trees, many of them large and mature, are exactly the trees that constrain the extensions, rebuilds and backland schemes that make up so much of the borough's residential planning workload. An arboricultural impact assessment in this part of Bromley is usually about mature specimen and garden trees on tight plots, frequently protected by TPOs.

The southern half is a different world of trees again. Here the landscape climbs into the North Downs and the ancient woodland around Downe, Cudham, Keston, Chelsfield and Biggin Hill — the same small-fielded, hedge-and-wood countryside in which Charles Darwin lived and worked at Down House, and much of which is Green Belt, some of it Sites of Special Scientific Interest, and some ancient woodland carrying the highest protection in the planning system. High Elms Country Park, Jubilee Country Park, Petts Wood and Hayes Common are all part of this deeply wooded southern half. Trees here are not just amenity features; they are habitats, landscape and, in the case of ancient woodland, irreplaceable.

For an arboricultural impact assessment, this context is the whole point. It means trees are one of the most significant material considerations in almost any Bromley application, that the council has more expertise and more expectation on trees than most, and that the standard of assessment has to be correspondingly high. It also means the specifics matter enormously: whether your trees are protected, whether you are near a conservation area or ancient woodland, and how good the trees really are. Knowing exactly where your site sits in Bromley's green map — its TPOs, its conservation areas, its proximity to protected woodland — is the foundation of an AIA that stands a chance, which is why we always start with the site.

A Tree Preservation Order (TPO) is a legal instrument made by a local planning authority to protect a specific tree, group of trees or woodland that makes a significant contribution to the amenity of an area. Bromley has an unusually large number — well over two thousand TPOs across the borough — reflecting how much its trees matter to its character. A TPO makes it an offence to cut down, top, lop, uproot, wilfully damage or wilfully destroy the protected tree without the council's written consent. Given how many there are in Bromley, checking whether any tree on or near your site is subject to a TPO is one of the very first things we do.

The law sits in Part VIII of the Town and Country Planning Act 1990 and in the Town and Country Planning (Tree Preservation) (England) Regulations 2012, which came into force on 6 April 2012 and created a single, consolidated procedure for all TPOs. Under this regime, works to a protected tree need a formal application for consent to the council, and Bromley can grant, refuse or grant with conditions — including a condition requiring a replacement tree. Where a protected tree is removed with consent as part of a development, the arboricultural documents are exactly where that is planned, justified and mitigated.

The penalties for breaching a TPO are severe, and they are meant to be. Anyone who, in contravention of an Order, cuts down, uproots or wilfully destroys a tree, or wilfully damages, tops or lops it in a way likely to destroy it, is guilty of an offence under section 210 of the 1990 Act, liable on summary conviction to a fine of up to £20,000 and, on conviction on indictment, to an unlimited fine. In setting the fine the court can take into account any financial benefit gained — so an owner who fells a protected tree to make a plot easier to develop can expect a penalty designed to remove that gain entirely. There is also a statutory duty to plant a replacement tree where a protected tree is unlawfully removed.

There are narrow exceptions — trees that are genuinely dead or that present an immediate danger, works required under other legislation, and works to implement a full planning permission — but they are limited and easily overstepped, and Bromley expects to be notified even where an exception is claimed. The practical message for anyone developing in Bromley is simple: assume the trees may be protected, check before you touch anything, and let the arboricultural assessment plan any tree work properly. The cost of getting it wrong, financially and to the reputation of your application, is out of all proportion to the cost of doing it right.

Beyond individual TPOs, Bromley has forty-seven conservation areas, and within a conservation area the law protects trees automatically, whether or not any specific Order applies. Under section 211 of the Town and Country Planning Act 1990, anyone proposing to cut down, top, lop, uproot or otherwise carry out work to a tree in a conservation area must give the council six weeks' written notice — a 'section 211 notice' — before doing so. This gives Bromley the opportunity to decide, during those six weeks, whether to make a Tree Preservation Order to protect the tree permanently.

This blanket protection catches a great many Bromley trees, because so much of the borough's most attractive suburban and village fabric is within conservation areas — from the historic cores of Chislehurst, Beckenham, Hayes and West Wickham to rural conservation areas around Downe, Cudham and Keston. If your project is within a conservation area, you should assume that any tree affected is protected in this way, that a section 211 notice or, where the works form part of a planning application, proper arboricultural documentation is required, and that the council will look at trees with particular care.

When notifying works to a conservation-area tree, the council expects the notice to describe the nature and extent of the proposed work — with pruning expressed in accordance with BS3998, the British Standard for tree work — together with a sketch plan showing the location of the tree and, usually, photographs. Carrying out work to a conservation-area tree without giving the required notice is an offence, carrying the same severe penalties as a TPO breach, so the six-week notice is not a formality to be skipped in a hurry to start on site.

For an arboricultural impact assessment, the conservation-area dimension means two things. First, the survey and assessment have to identify clearly which trees are protected by virtue of the conservation area, not just by individual Orders. Second, any tree work bound up with the development has to be planned so it can be authorised lawfully — through the application itself where it forms part of the permitted scheme, or through the section 211 notice procedure where it does not. Getting that right is part of what a properly prepared AIA delivers in a borough with as many conservation areas as Bromley.

Bromley's statutory development plan is the Bromley Local Plan, adopted on 16 January 2019, used alongside the London Plan to determine applications. Its 'Valued Environments' chapter sets out the borough's approach to trees, landscape and biodiversity, and it is unusually protective — as you would expect from the capital's most wooded borough. It is here that the Local Plan sets the expectation that where development proposals threaten to affect important or significant trees, the council will require a tree survey and arboricultural implications assessment prepared in accordance with BS5837:2012. That policy is the direct local basis for the AIA requirement.

The Local Plan's tree and landscape policies do more than require assessment. They expect development to retain trees of value wherever possible, to justify any losses, to protect retained trees during construction (typically through conditioned tree protection plans and method statements), and to provide replacement and new planting so that the borough's tree stock is maintained or enhanced. Significant and ancient hedgerows are given similar protection, with the council using planning conditions to safeguard them during building works. The direction of travel is unmistakable: keep the good trees, justify anything you lose, and plant to compensate.

Bromley's commitment to trees is visible beyond the Local Plan too. The council's Tree Management Strategy for 2023 to 2027 sets out twenty-five policies for managing the borough's trees, and its 'Treemendous' programme planted around five thousand additional street trees between 2021 and 2024, alongside new micro-forests in parks and greenspaces. This is a council that plants trees enthusiastically and protects them firmly — which tells you a great deal about how it will view an application that proposes to remove them. An AIA that respects that ethos, keeping and protecting trees and mitigating any losses, is speaking the council's own language.

The wider policy context reinforces all of this. National planning policy, through the National Planning Policy Framework, gives ancient woodland and ancient and veteran trees the highest protection — treating them as irreplaceable habitats whose loss should be refused save in wholly exceptional circumstances, with compensation not counting in the balance. And the mandatory biodiversity net gain regime, requiring most developments to deliver at least a 10% net gain in biodiversity, adds a further reason to retain trees and plant new ones. In Bromley, with its ancient woodland in the south, these national duties bite hard, and a good AIA is written with them in view.

An arboricultural impact assessment is rarely the only document supporting a Bromley application, and its real value shows in how it connects to everything else. The AIA has to agree with the architectural drawings — the trees retained on the site plan are the trees the AIA retains, the RPAs respected in the layout are the RPAs the AIA assesses, and the building footprint the arboriculturist analyses is the footprint the architect has drawn. When the design and the tree assessment are prepared together, that alignment is automatic; when they are prepared in isolation and stapled together at the end, the contradictions are exactly what a tree officer spots.

The AIA also interlocks with the other environmental documents a scheme may need. On many Bromley sites it sits alongside an ecological assessment — because trees are habitats, and features such as bat roosts and nesting birds have their own legal protection — and alongside the biodiversity net gain assessment that most schemes now require, where retained and new trees contribute to the habitat calculation. On sites with basements or significant excavation, the arboricultural constraints feed into the structural and drainage design. The AIA is a piece of a coordinated environmental case, not a silo.

For validation, the AIA is one of the documents Bromley checks the application against, so it has to be complete and correct at submission. A design and access statement, where required, will refer to the trees and to how the design has responded to them; the site and landscape plans will show the retained trees, the protection fencing and the new planting; and any tree work will be reflected consistently across the drawings and the reports. A well-assembled application reads as one coherent story about the site, of which the trees are a central chapter.

The deepest way the AIA fits the application, though, is that in Bromley it often shapes the application rather than merely supporting it. Because trees carry so much weight here, the tree constraints frequently determine where the building can go, how big it can be, and whether the scheme is viable at all. Treating the AIA as an integral part of the design process — bringing it forward, letting it inform the layout, and coordinating it with everything else — is how a Bromley application is built to succeed, rather than assembled and hoped through.

For an extension in Bromley's leafy suburbs, the tree question is usually about the mature trees on and around a tight plot. A rear extension on a Beckenham or Chislehurst villa can easily reach into the RPA of a large boundary tree — the owner's own, or a neighbour's — and the AIA has to show whether the extension can be built without unacceptable harm, often using special foundations to avoid disturbing roots. Many of these trees are protected by TPOs, so the assessment also has to plan any pruning or work lawfully. Bringing the tree survey forward here frequently changes the size or position of the extension for the better before it is ever drawn.

For a knock-down-and-rebuild, the trees can be the making or breaking of the whole plot. Replacing a modest house with a larger one on a wooded suburban plot means the new footprint has to fit within the space the trees leave, and the demolition and rebuild have to be sequenced to protect retained trees throughout. The AIA and the tree protection plan are central, because a rebuild involves heavy machinery, deep excavation and prolonged site activity — all of which threaten trees — and because the loss of a good tree to make room for a bigger house is exactly the kind of proposal Bromley resists.

For backland and garden-plot development — squeezing a new dwelling behind or beside an existing one, a common Bromley pattern — trees are very often the decisive constraint. Garden plots in this borough are typically well treed, frequently with protected trees, and the combined RPAs can leave little developable ground. The AIA determines whether a viable dwelling can be fitted between the trees at all, whether the access can be built without harming roots, and whether the losses needed are justifiable. Many backland schemes live or die on the arboricultural assessment, and doing it first tells you whether the plot is worth pursuing.

For new houses on the wooded fringes of the south of the borough, the stakes rise again. A plot near ancient woodland, or within or beside a conservation area, faces the highest tree protection in the system, and the AIA has to engage the buffer expectations for ancient woodland, the categorisation of high-value trees, and the openness and landscape sensitivities of the Green Belt countryside. Here the tree assessment is inseparable from the wider planning case, and a rigorous, honest AIA that keeps the important trees and protects the woodland is often the price of any consent at all.

The most common and most avoidable mistake is designing first and surveying the trees afterwards. Owners and inexperienced designers draw the scheme they want, submit it, and only then discover — from the arboriculturist or from the council — that the extension sits on a protected tree's roots or that the layout requires the loss of a category A tree the council will never accept. By then the design is committed and the choice is an expensive redesign or a refusal. BS5837 exists precisely to prevent this, and bringing the survey forward is the single biggest improvement most tree-affected schemes can make.

The second common failure is an inadequate or missing assessment at validation. Submitting a Bromley application affecting trees without a proper BS5837 survey, AIA and (where needed) protection plan means the application is not validated, and the clock does not start until the gap is filled. Worse, a superficial 'tree report' that does not follow BS5837 — no proper categorisation, no calculated RPAs, no real impact analysis — will be given little weight and may simply be rejected, wasting the fee spent on it. Half a tree assessment is often worse than none, because it looks like an attempt to do the minimum.

A third failure is over-optimistic categorisation and unjustified losses. Grading mediocre trees down so they can be removed, or glossing over the impact on a good retained tree, produces an assessment the council will not trust — and Bromley's tree officers are experienced enough to see through it. Removing a category A or good category B tree without a compelling arboricultural and planning justification, or without proper replacement planting, is one of the surest ways to attract a refusal in this borough. Honesty in categorisation and realism about losses are not just ethical; they are tactical.

The fourth, which bites after permission rather than before, is failing to implement the tree protection properly on site. A permission granted subject to a conditioned tree protection plan and method statement is only lawful if those measures are actually installed and followed — the fencing put up before demolition and kept up, the RPAs kept clear, the approved working methods used. Contractors who ignore the protection can damage or kill the very trees the application relied on, breach the condition, and, where protected trees are involved, expose the owner to prosecution. A protection plan is only as good as its enforcement on the ground.

An arboricultural impact assessment rarely travels alone. On most tree-affected Bromley schemes it forms one part of a small suite of BS5837 documents: the tree survey and schedule that underpin it, the tree constraints plan that maps the trees, and — where trees are retained near construction — the arboricultural method statement and tree protection plan that follow it. Together these make up the full arboricultural package, and Bromley may want all of them, either at application or secured by condition for the AMS and TPP.

Beyond the tree documents, ecology is the closest relation. Trees are habitats, and features such as bat roosts, nesting birds and, in the south of the borough, links to ancient woodland engage separate legal protections and often a preliminary ecological appraisal or protected-species survey. Because a scheme that removes or works near trees can affect these features, the arboricultural and ecological assessments have to be consistent with each other, and on many Bromley sites both are needed. Where trees or hedgerows are removed or created, they also feed into the biodiversity net gain assessment that most developments now require.

On the design side, the AIA is reflected in the architectural and landscape drawings — the site plan showing retained trees, protection fencing and new planting, and often a dedicated landscape or planting plan proposing the replacement and new trees that mitigate any losses. Where the site has basements, retaining structures or significant level changes, the arboricultural constraints feed into the structural and drainage design, because foundations and services within or near RPAs need special detailing. And a design and access statement, where required, ties the arboricultural response into the overall design narrative.

We coordinate this whole set so it tells one consistent story. It is common, when documents are prepared by separate consultants who never speak to each other, for the tree report to retain a tree the landscape plan removes, or for the ecology survey to assume a tree the AIA fells. Those contradictions are precisely what a Bromley case officer notices and holds an application up over. Preparing the arboricultural assessment as part of a coordinated package — architecture, trees, ecology and biodiversity aligned — is how we avoid that and keep the application moving.

The cost of an arboricultural impact assessment depends chiefly on how many trees are involved and how complex the site is. A modest extension affected by one or two boundary trees needs a smaller survey and assessment than a backland plot ringed by mature protected trees, or a new house near ancient woodland with a long tree schedule and detailed protection design. Because Bromley sites are so often well treed, the survey can be substantial — but it is also proportionate: the arboriculturist records what is relevant to your specific proposal, not every tree for miles. We scope the work to your site and give you a clear fee before it begins.

There is no separate council fee for the arboricultural documents themselves — they are part of your planning application, whose fee is set nationally and payable to Bromley on submission — but there are related costs to budget for. If protected-tree works are involved, an application for consent to work on TPO trees, or a section 211 notice for conservation-area trees, may be needed. Where the AIA identifies ecological features, a separate ecological survey may follow. And on sensitive sites, arboricultural supervision during construction is an additional, though usually modest, cost that protects a much larger investment.

On timescales, the survey itself is quick once the arboriculturist can access the site — typically a site visit and then the schedule, constraints plan and report produced over a couple of weeks. The real timing benefit, though, comes from doing it early: an AIA prepared before the design is fixed shapes the layout and avoids the far larger delay of a redesign or a refusal later. An AIA commissioned in a panic after a validation query, by contrast, holds the whole application in limbo until it is delivered, so front-loading the tree work almost always saves time overall.

It is worth being clear about where money is really lost on tree-affected schemes in Bromley. It is not on a thorough survey and a well-judged assessment. It is on buying or committing to a plot whose trees make it undevelopable; on a design that has to be torn up because the trees were assessed too late; on a refusal because the loss of a good tree could not be justified; or on damaging a protected tree during construction and facing prosecution and a replacement duty. Spending properly on getting the arboricultural assessment right, and early, is the most cost-effective way to develop among Bromley's trees.

The process starts with feasibility, and on a tree-affected Bromley site this stage does a lot of the work. We establish what trees are on and around the site, check whether any are protected by a TPO or by a conservation area, look at proximity to ancient woodland and other designations, and form an early view of whether the trees will constrain the scheme and what the AIA will have to show. This is where we tell you honestly whether the plot can take the development you have in mind, and how the trees will shape it — before you commit to a design.

We then commission or carry out the BS5837 tree survey and produce the tree constraints plan, and we design the proposed scheme on top of it, so the layout responds to the trees from the start. Where the trees allow the scheme with care, we develop the design to fit; where they do not, we adjust it — moving the footprint, using special foundations, or reconsidering the ambition — rather than pressing on with a layout the trees will veto. Designing with the constraints plan is the heart of getting a Bromley tree case right.

Bromley offers pre-application advice, and on a genuinely tree-sensitive scheme — a backland plot, a scheme proposing to remove protected trees, or a site near ancient woodland — it is often worth using. A written steer from the council's officers, including its tree officers, flags concerns while the scheme can still be adjusted and shows the eventual case officer that the proposal has been developed carefully. We advise whether pre-application is worthwhile and prepare it where it adds value.

We then prepare the full application — the architectural drawings, the arboricultural impact assessment, the tree protection plan and method statement, and the other supporting documents the site needs — and submit it to Bromley through the Planning Portal, managing it through validation and determination. We respond to the case officer's and tree officer's queries, provide additional information, and negotiate amendments where they will secure a positive decision. Once permission is granted, we help discharge any tree-related conditions and make sure the protection measures are ready to be implemented on site — so the trees the application relied on actually survive the build.

To make it concrete, consider a common Bromley scenario: an owner of a large Edwardian house in Beckenham wants to build a new dwelling in the rear part of the garden — a backland plot — served by a driveway down the side of the existing house. The garden is generously treed, as Beckenham gardens are, with a mature oak on the rear boundary, a large lime beside the proposed access, and several smaller trees dotted through the plot. It is exactly the kind of project where the trees, not the design, decide the outcome.

At feasibility, we check the trees and find that the oak and the lime are both covered by a Tree Preservation Order — unsurprising in this borough — and that the plot is not in a conservation area. We commission a BS5837 survey. The oak is categorised A, the lime B, and the smaller trees a mix of C and one U. The survey plots each tree and its root protection area onto a constraints plan, and the picture is immediately clear: the oak's RPA reaches well into the buildable ground, the lime's RPA overlaps the intended driveway line, and the developable envelope between them is tighter than the owner had assumed.

That constraints plan drives the design. We position the new dwelling to sit clear of the oak's RPA entirely, keeping the borough's best tree untouched; we design the driveway past the lime using no-dig, cellular-confinement construction so the access can cross the edge of the lime's RPA without excavation or compaction that would harm its roots; and we take the losses from the category C and U trees only, proposing replacement planting to more than compensate. The scheme that emerges is smaller and better placed than the owner's first idea — but it is one the trees can accommodate, which the first idea was not.

On the application, the AIA sets out the retained oak and lime, justifies the modest losses, and demonstrates that the retained trees will survive; the tree protection plan shows protective fencing around the oak and the ground-protection and no-dig detail at the lime; and the method statement specifies how the driveway is built and how the trees are protected through construction, with arboricultural supervision of the works near the lime. Submitted through the Planning Portal and managed through Bromley's determination, a scheme like this goes in as a considered, tree-led proposal the council can support — rather than an over-ambitious layout that the oak alone would have defeated. Once approved, the conditioned protection measures carry the trees safely through the build.

The south of Bromley contains something the rest of London has very little of: genuine ancient woodland, together with the ancient and veteran trees that go with an old wooded landscape. Ancient woodland is land that has been continuously wooded since at least 1600, and it is treated in national policy as an irreplaceable habitat — its ecological complexity cannot be recreated, so its loss cannot be compensated for by planting elsewhere. The National Planning Policy Framework gives ancient woodland, ancient trees and veteran trees the highest level of protection, and development that would result in their loss or deterioration should be refused unless there are wholly exceptional reasons.

For a residential scheme anywhere near this landscape — a plot backing onto woodland around Petts Wood, Hayes Common, Keston or the North Downs villages — the arboricultural assessment has to take ancient woodland into account directly. Standing advice from the government expects development to keep a suitable buffer between the built form and ancient woodland (commonly at least fifteen metres, and often more depending on the scheme), to avoid indirect harm from drainage, lighting, root disturbance and the everyday pressures a new house brings to a woodland edge, and to design in a way that protects the woodland's long-term integrity. The AIA is where that buffer and those protections are set out.

Veteran and ancient individual trees — the great old oaks and other trees that a landscape like Bromley's south still holds — carry a similar irreplaceable status. They have exceptional biodiversity, cultural and landscape value, and their loss or serious harm is treated as unacceptable save in wholly exceptional circumstances. Where such a tree is on or near a site, the arboricultural assessment has to identify it as veteran, calculate a generous root protection area appropriate to its age and importance, and design to protect it absolutely. The government advises seeking advice from a registered arboriculturist before any work near veteran trees, which is precisely the expertise a proper AIA brings.

The practical point for anyone developing in the greener south of Bromley is that ancient woodland and veteran trees raise the bar significantly. A scheme that respects them — keeping a proper buffer, protecting the roots and canopies, avoiding indirect harm — can succeed; a scheme that encroaches on them is very likely to be refused. Identifying this constraint at the outset, and designing around it honestly, is one of the most important things an AIA does in this part of the borough, and it is not an area for guesswork or wishful thinking.

Alongside the long-standing tree protections, a newer duty now shapes how development treats trees: biodiversity net gain (BNG). Introduced through the Environment Act 2021 and mandatory for most developments since early 2024, BNG requires a development to deliver a measurable improvement in biodiversity — at least a 10% net gain, calculated using the statutory biodiversity metric, and secured for at least thirty years. Trees, hedgerows and woodland are significant habitats within that metric, so retaining existing trees and planting new ones directly affects whether a scheme meets its BNG obligation.

This changes the calculus around trees in a helpful direction. Where once the pressure was simply to protect trees, now there is an additional, quantified incentive to keep them and to plant more: retained mature trees carry high habitat value in the metric, and their loss has to be made up elsewhere, often at cost. For a Bromley scheme, where trees are abundant and valued, coordinating the arboricultural assessment with the BNG assessment means the trees you keep and the trees you plant are working for both the tree case and the biodiversity case at once.

Smaller householder applications — a typical extension — are generally exempt from the formal mandatory BNG requirement, but the underlying expectation to protect and enhance biodiversity, and Bromley's own policies favouring tree retention and replacement, still apply. For larger residential schemes — new dwellings, backland development, multiple units — BNG is a live obligation, and the arboricultural documents and the biodiversity assessment have to be prepared together so that the trees are counted consistently and the net-gain figure is real. A tree the AIA fells cannot be a tree the BNG metric assumes retained.

The broader message is that trees now sit at the intersection of several duties in Bromley: the borough's own strongly protective Local Plan policies, the legal protections of TPOs and conservation areas, the highest national protection for ancient woodland and veteran trees, and the mandatory biodiversity net gain regime. A modern arboricultural impact assessment is written with all of these in view, so that the treatment of trees satisfies not just the tree officer but the whole framework the application has to pass through. That integrated approach is what a good AIA delivers.

Crown Architecture works on residential projects across Bromley and its surrounding Kent and Surrey fringe, and we treat trees the way this borough demands: as a central design constraint, not an afterthought. We coordinate the architecture and the arboricultural assessment together, bringing the tree survey and constraints plan forward so the design responds to the trees from the first sketch — which, in a borough this wooded, is the single most important thing you can do to give a scheme its best chance. Splitting the design from the tree assessment is how Bromley applications go wrong; joining them up is how they succeed.

We know the Bromley context intimately: the leafy suburban north with its mature protected garden trees, the deeply wooded south with its ancient woodland and Green Belt, the borough's forty-seven conservation areas and its thousands of TPOs, and a council that plants trees enthusiastically and protects them firmly. We use that knowledge to give you honest advice at feasibility — including telling you when the trees make a plot or a scheme unworkable — and to prepare arboricultural assessments and tree protection strategies that engage the council's genuine concerns rather than trying to slip past them.

Just as importantly, we prepare a coordinated, self-consistent package. The trees retained on the drawings are the trees the AIA retains and the protection plan protects; the RPAs respected in the layout are the RPAs assessed and fenced; the losses proposed are justified and mitigated with replacement planting; and the ecology and biodiversity documents line up with the tree case. A case officer and a tree officer can read our applications as one coherent story about the site, which is exactly what they need to be able to approve them without filling in the gaps.

And we stay with the project. We manage the application through Bromley's validation and determination, respond to the case officer and the tree officer, negotiate amendments where that will secure a positive decision, and — once permission is granted — help discharge the tree-related conditions and make sure the protection measures are actually implemented on site, so the trees the whole application depended on survive the build. The aim is a single, accountable point of contact from the first tree survey to a completed home that sits comfortably among Bromley's trees. It all starts with a free, no-obligation quote.