What does a tree survey entail and do I need one?
What does a tree survey entail?
Trees offer several core benefits including adding value to a site, benefitting the environment and maintaining ecosystems. They are also aesthetically pleasing, and some hold cultural and historical value, such as the Major Oak in Nottingham’s Sherwood Forest. Likewise, removing a tree can have a detrimental effect on the ecosystem. For instance, any occupying animal species will lose their habitat and the chance of flooding in high-risk areas will increase as trees help to bind the ground together and soak up excess water. As trees also improve air quality by producing oxygen and absorbing carbon dioxide, removing a tree can also seriously impact the effectiveness of photosynthesis.
As a developer, architect or site owner, you may find that your development project is going to impact trees on the site, and if that is the case, you are going to need a tree survey.
How does a tree survey work?
Conducted by an experienced and qualified professional arboriculturist, the first step in the process is what is known as a BS5837 tree survey or a stage one survey. UK planning authorities are required to check the potential impact that a new development could have on trees and their environment. A BS5837 tree survey is a British Standard survey that is designed to carry out the relevant checks, and it is required for any construction, demolition or design work that could potentially infringe on trees.
Before the survey begins, the arboriculturist will ask you a few questions regarding your development in regards to what you are planning to do on the site, as well as details of where and how you plan on carrying out the development. At this point, you will be asked to provide a site plan, often as the result of an ordnance survey or topographical survey. Once all of the relevant information has been exchanged, the arboriculturist can then come to your site to conduct the survey.
The purpose of the BS5837 survey is to inform you and your local planning authority of the practical constraints to your site and development, both above and below ground. Once on the site, the survey is undertaken using a selection of professional equipment including a Pocket GIS, PT Mapper Pro, Trimble Juno 3b and a TreeMinder. From these devices, data on core areas such as the tree species, condition and spatial information will be gathered and stored securely. The arboriculturist can then plot the trees on top of your site plan to create a real-world overview of the site.
Tree retention categories
All trees on or adjacent to your site will be assigned what is known as a BS5837 retention category. Tree retention categories are likely to be the most important form of data you will receive from the tree survey, and the category will define the specific circumstances of each tree.
Category A is the highest classification of a tree, and it means that it is in good health, prominent and has important qualities such as the ability to support ecosystems and add cultural value. Within this category, they are expected to have a remaining contribution of over forty years. As a general rule, no local planning authority will let you carry out work above or below ground within distance of these trees unless there are mitigating circumstances.
Category B is a similar classification to category A. However, category B trees are expected to have a remaining contribution of around twenty years. If possible, local planning authorities like to see category B trees preserved. If they do need removing, however, compensatory planting can be achieved.
Category C is intended for trees that are in poor condition, typically not considered a risk for planning, and only have around ten years of contribution left. However, despite this, your local council may still want a compensatory tree planting in its place after removal.
Category U is a classification that applies to trees that are dead or dying and pose a safety risk. They are usually expected to have a remaining contribution of less than ten years, and whether or not they interfere with your site or development, they should be removed regardless.
It is also important to note that replacing ecological contributions to the environment such as trees are not just for maintaining an aesthetically pleasing look, but also to provide a home and food source to a variety of animals such as bats, birds and insects.
What is a Root Protection Area?
Another important consideration during a tree survey is the impact a development could have below ground. To determine this, the arboriculturist will use what is known as a Root Protection Area (RPA) – a calculation that is used to gauge the rooting environment for the specific tree in question. Calculated by multiplying the diameter of the stem above ground by 12, the radius of the tree’s rooting environment can then be used to determine what areas to avoid when carrying out the development.
A method of potentially reducing the RPA is through a procedure called ‘air spading’ that involves blasting a jet of high-pressure air at the ground to form a trench. The soil can then be displaced without damaging the roots, and the roots can be better exposed to make the RPA reading more accurate.
If your development plans fall within the RPA and pose danger to the corresponding tree, there will be the need for an Arboricultural Impact Assessment (AIA). This predominantly covers three areas of potential conflict - above ground, below ground and on the tree crown. If necessary, undertaking an AIA is not only required to support your planning application, but also to raise any issues and ensure that you remain within your budget and schedule.
Why a tree survey is important in your development project
Once the BS5837 survey is completed, you will submit the report the arboriculturist produced to your local planning authority. The report will outline each tree based on their retention category classifications before demonstrating how your development will protect higher quality trees and mitigate the loss of lower quality trees. As a result of this assessment, you may need to replace trees that were removed during the development. With the information provided by yourself and the arboriculturist, your local planning case officer will then base their decision on the evidence and existing policy.
It is at this point that the importance of the tree survey and any other required arboriculture surveys will come to light as, if the correct surveys haven’t been carried out and the accompanying report hasn’t been passed on to the local planning authority, your development will be refused planning permission. For more information, visit Arbtech.
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