Tree Root Size Charts – Do they exist and are they accurate?

We are often asked for tree root size charts or tables to determine where the roots of trees are located in relation to the size, height, or species of tree. While there are no species-specific tree root size tables or charts relating to the above, the best resource that homeowners, planners, and consultants have is within the document – British Standards: 5837:2012 – Trees in relation to design, demolition and construction – recommendations (BS.5837:2012)

Within this document, it states that in order to determine the Root Protection Area (RPA), or the area where the most important rooting activity is taking place you should calculate this as follows:

“For single stem trees, the RPA should be calculated as an area equivalent to a circle with a radius 12 times the stem diameter”

The above calculation means a tree with a diameter of 500mm DBH has a calculated RPA of 6m radius surrounding the tree and the total area encompassing the RPA is 113m2. A much larger tree with a DBH of 1000mm would have a calculated RPA radius of 12m and a total area of 452m2.

This simple calculation gives an estimate of the RPA of the trees, however, it does not take into account site or species-specific information such as impacts to root growth such as utilities, buildings etc.

Within the scope of BS.5837:2012 there is scope for adopting a modified RPA, although typically this can only be modified by 20% of the standard calculation.

What does this mean for trees?

In essence, this means that trees on construction or development sites are being given arbitrary protection from damage or in many cases unnecessarily impeding design and construction in areas where no rooting activity is taking place.

How can we gain an accurate understanding of where tree roots are located?

At Arboraeration we understand the balance between tree retention and protection, and the need for development in the urban environment. Based on this we have a number of options for our clients in order to gain an accurate understanding of the location, size, and type of roots that are found and show where active construction will not negatively affect the trees.

Airspade investigations

Using our airspade we can safely and efficiently excavate trial pits to physically see where tree roots are located, measure their diameter and offer advice on options of root pruning and site suitability. When used correctly by an experienced operator airspades do not cause damage to tree roots and are ideally suited to this task.

The airspade is ideally suited to smaller areas of 1-12m long trial pits and typically used when predesigned plans are encroaching onto the RPA of trees.

Tree Radar

Arboraeration are please to say that we are one of the few companies in the UK to be able to offer Tree Radar Surveys of tree roots and sites. This type of survey uses Ground Penetrating Radar (GPR) to plot the location, depth and size of tree roots accurately and quickly.

Results of these surveys are presented in easy to read diagrams and can even be uploaded onto topographical surveys.

Tree Radar surveys are used in larger areas, or where soil excavations cannot take place (Such as highways, footpaths, beneath existing foundations, etc) or when there are multiple retained trees on-site and an accurate picture is required.

If you wish to find out more information please feel free to Email Us or call on 02071 834 473

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