The British Standard "Trees in Relation to Design, Demolition and Construction to Construction - Recommendations" (BS 5837) (2012), details the steps that should be taken to ensure that trees are appropriately and successfully retained when a development takes place.
This means that where there are trees either on a potential development site or within close proximity to the site, the district council will consider them when making decisions on planning applications for that site.
Planning applications and the development that may follow should, where appropriate follow the processes and recommendations laid out in BS5837 (2012).
Full copies of BS 5837 are available to purchase from the British Standards Institution.
There are several elements of BS 5837 that are vital when considering a development site that contains trees or has trees in close proximity.
Tree Constraints Plan
The first and most vital stage in the design and layout of any site is the creation of a Tree Constraints Plan.
The early availability of a Tree Constraints Plan to the development design team will benefit the developer by:
- Reducing redesign time as trees will be identified before the initial design is drawn up
- Reducing the risk of applications not being registered by Development Control
- Reducing the risk of tree issues being raised during the planning application process
- Increasing the speed at which tree issues can be dealt with during the application process
The Tree Constraints Plan should be a combination of the information gathered during a topographical survey (location of all trees, shrubs and hedges and other relevant features such as streams, buildings and spot level heights) and an accurate tree survey.
The tree survey should be carried out in accordance with BS 5837 (2012), and contain the following information about each tree on the site that has a stem diameter above 75mm measured at 1.5m above ground level, and those trees of smaller diameter that are of particular interest or potential value:
- A tree reference number (this should relate to the to the Tree Constraints Plan)
- Tree species
- Stem diameter taken at 1.5m from ground level (Diameter at Breast Height)
- Branch spread (in four directions North, East, South and West)
- Height of crown clearance above ground
- Age class
- Physiological condition
- Structural condition
- Preliminary management requirements
- Estimated safe useful life expectancy
- Category grading (see BS 5837)
It is important to remember that the parts of a tree that lie below the soil surface, its roots, are just as important as those above ground (trunk, branches, leaves).
Every effort should be made to ensure that the roots of retained trees are not damaged during the construction process.
Root problems can lead to a decline in a tree's health resulting in the need for a tree to be removed or even structural collapse.
Tree roots can be easily damaged by:
- Crushing by vehicles/plant equipment and/or storage of building materials or soil
- Compaction of the surrounding soil leading to root death by asphyxiation (lack of oxygen) or drought (inability to obtain water)
- Severing and removal of roots by excavation
- Poisoning from spillage or storage of fuel, oil, chemicals etc.
- Changes in soil levels around trees resulting in root death as a result of exposure or asphyxiation
- Installation of impermeable surfaces leading to a decline in tree health due to lack of water
It is vital therefore that the Tree Constraints Plan should also clearly show the Root Protection Area of each tree.
A tree's Root Protection Area can be equated to a circle, using the tree as the centre-point, with a radius that is twelve times the tree's Diameter at Breast Height for a single stemmed tree, or alternatively ten times its basal diameter measured above the root flare for a multi-stemmed tree.
Tree Protection Plan
Trees are particularly vulnerable on development sites and may be affected either immediately if removal or pruning is necessary to accommodate a development, or in the longer term.
This may be as a result of disturbance during the development process or following pressure to remove or prune trees from the occupants of new buildings.
The design layout should take these issues into account.
Once it has been decided which trees, hedges or shrubbery are to be incorporated into a design layout it is important to ensure that they will survive the development process.
A Tree Protection Plan is an essential aspect of tree protection with regard to development.
The Tree Protection Plan is a scale plan showing:
- Any proposed or existing buildings or structures
- All retained trees both on and neighbouring the site and their corresponding Root Protection Areas and crown spreads (N, E, S and W)
- The location of protective fences or barriers (details of how these are to be constructed must also be supplied)
- Proposed location of all plant and materials storage
- Drainage runs, roads and driveways
- Existing and new accesses
- Any other surface or underground features that may affect the trees on or neighbouring the site
Arboricultural Method Statement
If construction or the laying of hard surfaces is allowed within the Root Protection Area of a tree, or if any part of the development process is likely to detrimentally affect any retained trees, then it is likely that an Arboricultural Method Statement will be required.
An Arboricultural Method Statement details the methodology for the implementation of any aspect of development, that has the potential to result in the loss of or damage to a tree, and explains how this damage will be avoided.