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.