BS5837 Tree Survey, Tree Constraints Plan

Two of our tree experts working on site.

A BS5837:2012 survey is essentially just a constraints exercise. It answers the question “do I need to protect any trees within or adjacent to my site?” Alternatively, put another way; “does my development scheme look defensible?”

The way we answer these questions is fairly simple and the best way to explain how we do this, is to reverse engineer the process. Your local planning authority has a Tree Officer, who is normally responsible for weighing the council’s policies on tree management against your development ambitions and providing a decision recommendation (grant/refuse permission) to your Case Officer. He or she will use British Standard 5837:2012 to guide this decision.

Therefore, to ensure that this recommendation is favourable, we work with you to ensure that your scheme provides for a sensible tree removal/retention balance. That means showing that you can retain and protect good quality trees on and adjacent to your site, while offering a thorough justification for accepting the loss of those of lesser quality.

This stage of work is often required simply to validate your planning application, distinct from an arboricultural impact assessment, or method statement and protection plan, which are more often than not required at later design and planning stages, or as conditions of consent.

How much does a tree survey cost?

Our BS5837 Tree Survey starts at just £349. We say ‘starts at’ because the price will vary depending on the size of your site, the number of trees, the location of the site and a few other factors such as the availability of our consultants.

More About Your  BS5837 tree survey

In this section you will find a little more detail, to help you understand more completely what your BS5837 survey is, and why it is important to get right, in order to guarantee you success at planning.

You’ll also find some internal and external links at the bottom of this page, should you want to read even more about trees and the planning process. In the overview, we talked about your BS5837 (originally published in 1980 as a ‘code of practice’, published as a ‘guide’ in 1991 and revised in 2005 and again in May of 2012) survey and constraints plan drawing being a ‘constraints exercise’, that is a function of our ‘tree quality assessment’.

So exactly how is that quality assessed? Well, far from being arbitrary, this quality assessment (among many other things) is exactly what BS5837 seeks to standardise. Here’s how it works: Your BS5837 survey is intended to inform your design team and local planning authority of the realistic constraints to your development presented by trees on and adjacent to your site, above and below ground.

The survey is undertaken using a Trimble® Juno handheld (Global Positioning System) location device and PT Mapper Pro, which stores both the schedule data (such as a tree’s highlight, species, conditions, etc) and the spatial information, enabling us to plot your trees on to your Ordnance Survey tile or topographical survey.

Our tree constraints plan drawing will be produced and issued to you in AutoCAD and PDF formats, so that your design team or architect can overlay it onto their own plans an drawings. You will also receive an interpretive report that identifies the surveyor and site, defines much of the methodology of BS5837 and summarises the general nature and condition of the tree stock surveyed. It looks something like this:

What do we require from you to do all of this? Not a lot.

• A time and a place
• Your site plan (e.g. a geo-referenced Ordnance Survey tile or topographical survey)
• That’s it!

BS5837 Tree Survey – The Need To Know

BS5837 retention categories are arguably the most important piece of data to you and your designers. They are definitely something you want to pay close attention to. All trees that are on and adjacent to your site will have a BS5837 retention category, which is a function of a tree’s size, health/longevity and amenity contribution. The better quality the tree, the more of a constraint it presents to development, and vice versa. Here’s a really simplistic overview of the BS5837 retention categories:

• Cat A – The most important trees. Normally these will be particularly good specimens, be prominent in the street scene, or have other important quality qualities (such as ecosystem services or cultural value – think Robin Hood and the Major Oak in Sherwood Forest). Generally Cat A trees will be estimated to have a remaining useful contribution of at least 40 years. These trees are effectively an outright constraint to development. No local planning authority – that we have come across – will let you incur above or below ground, within influencing distance of such a tree, unless you have a very, very good reason for doing so.
• Cat B – These trees should normally have a remaining useful contribution of at least 20 years and should be of similar quality to Cat A trees, perhaps with less historic, cultural and street scene significance. Think perhaps about a row of huge, mature lime (Tilia spp.) trees along a town centre boulevard. None are so significant or dominant as to be categorised A, yet they are otherwise sound and nevertheless make a significant amenity contribution to the urban landscape. Local planning authorities will normally wish to see Cat B trees retained – unless there are extenuating circumstances (for instance, building a school or clinic) and compensatory planting can be achieved. Building near these trees and even within root protection areas can be achieved by negotiation and with innovative use of engineering, such as piled or cantilevered foundations, and tree-friendly surface treatments, such as GeoSynthetics® CellWeb.
• Cat C – These trees are generally very low quality with a useful remaining amenity contribution of at least 10 years. Unless you intend to remove very large numbers of Cat C trees, their loss is not normally considered to be a planning risk and individually it is very rare for them to be a constraint to your development. However, it is still common for your local planning authority to seek compensatory planting in exchange for their removal.
• Cat U – These are trees that are either dead, dying or dangerous, or those with a useful remaining amenity contribution of <10 years. These tree do not represent a constraint to your development as they are considered to be of such low quality that they should be removed in any event, for reasons of sound arboricultural management.

Canopies and The Root Protection Area

Above we talked about BS5837 Cat A and B trees needing proper consideration in your development scheme, in order to eliminate your planning risk. Part of that consideration is protecting the tree, both above and below ground. Above ground, the constraints are fairly clear and obvious; the canopy is visible for all to see.

Protecting the canopy isn’t complicated, and can often be as simple as erecting a herras fence around the tree, with signage, so that plant and machinery do not damage it. So far so good. Below ground, things are a little different. A little less tangible. The so-called ‘root protection area’ is a calculated functional minimum of rooting environment that (the authors of BS5837) consider the tree needs to sustain itself. Calculated, meaning – it’s a guess, but at least it’s a calculated one!

The equation to compute the radius of the area when represented as a circle with the tree in the centre, is very simple – you take the diameter of the stem at 1.5m above ground level, and multiply it by 12. There are variations on this theme for multi-stemmed trees, but they are much of a muchness. So, if you have a tree that has a stem diameter of 0.5m, you need to avoid disturbing the ground around the tree up to 6m away from the stem.

We say avoid, because there are instances where it is possible, with a little tenacity, to justify some incursion into that area, for example for car parking, or even foundations. Why is all this necessary? Because roots, just like any other part of a tree, still need to respire at a cellular level and therefore require oxygen and gaseous exchange to take place, in order to survive.

As the model in the picture below demonstrates, most of your trees’ roots are in the top 600mm of soil, and almost none of them go down more than a metre. For this reason, they spread out in a network over a very wide area and are sensitive to compaction (squeezing the air spaces out of the soil) as well as direct loss by cutting.

Source: BS5837:2012

A couple more facts about root protection areas (RPA):

• They can be offset by as much as 20% under certain circumstances
• They must take account of restrictions to root development, such as basements
• The do not have to be circular
• They normally extend beyond the canopy of the tree

One Smart Way to (Potentially) Reduce Your RPAs

Over the years, we have perfected the art of reducing root protect areas drastically, by proving roots are not present, via a process known as ‘air spading’ – blasting a very high pressure jet of air at the ground to excavate a trench, say where you’d like to build up to, which has the effect of displacing the soil without damaging roots.

This information can sometimes be vital as it can literally knock metres off an RPA’s radius. In some areas of London where the value of property is in the thousands of pounds per square foot, having one of our arboriculturists investigate a calculated (=theoretical) root protection area with an air spade to obtain an objective (=actual) root distribution, can pay for itself many times over, improving the profitability of your development.

Of course, this can be a double edged sword, by actually confirming the tree survey and constraints plan’s indication of rooting volume on your site, but in the umpteen times we’ve used the air spade, it’s only happened a couple of times and frankly, since you’re no worse off than when you started, it’s use on contentious sites is a no-brainer. Here’s a really short clip of Arbtech and the air spade in action: