Preserving mature trees improves land value and environmental quality. Established trees give a feel of maturity to a new development and enhance the sustainability of our environment. The council is developing strategies to enhance tree management in North Lincolnshire. As part of this approach it has adopted the Trees and Development Supplementary Planning Guidance (SPG).
To grow, trees need a balance of moisture, nutrients and air. Changes in light levels, soil composition and structure easily disturb this microclimate. Trees are easily damaged. Unplanned and poorly controlled site works can easily cause the rapid decline and death of trees.
Retaining trees needs accurate and detailed information. Before deciding anything about the development of a site it should be properly surveyed. This information can then be used in all other site development matters.
Site survey information is then used to produce a tree survey. This plots the exact position of all trees and hedges and provides accurate information on the crown spread and trunk girth of each. The species, health and amenity value of the trees are then assessed by an arborist to identify trees worthy of retention.
Tree protection during construction
It is vital to protect identified trees before any work starts.
Over 90 per cent of tree roots are very close to the soil surface (within 600mm). Significant damage is caused by plant and machinery used in site clearance as this compacts the soil. Raising ground levels around trees also smothers roots.
Sturdy fences should be erected to enclose the area covered by the spread of the branches, or an area equal to half the height of the tree, whichever is the greater. These areas must then be left undisturbed during site works:
- nothing should be stored or sited in them
- vehicles should not be allowed to pass into them
- fires must not be lit within them or within scorching distance of tree canopies.
Buildings
The relationship between buildings and trees can be beneficial to both if considered at the design stage. Building works can damage roots and buildings can rob trees of light, and vice versa. So, on sites with trees, it is in everyone’s interest to get the design and siting of buildings right.
Qualified arborists can advise on where best to site buildings. Where possible, buildings should be set away from the crown spread of trees, sited to the south of large trees or trees that will become large. *
Similar consideration applies to other issues related to preserving soil structure around trees. These include:
- temporary site access
- general site access
- ways of working within exclusion zones when this is the only possible way of proceeding.
Soil type
This is important in determining distances between trees and new buildings. It should be established as a matter of course through site investigation. Where it is not possible to build away from trees to be retained, root barriers or novel foundation constructions may be a way forward. **
Site works and service provision
Avoiding root disturbance will ensure the successful retention of trees and hedges. Site works such as trenching for foundations, service runs and road construction should be kept well clear of established zones. Properly designed service provision using common service trenches will also save money.
* The Trees and Development SPG provides a means of calculating how far a building should be sited away from the tree(s) to be retained.
** Novel foundations will require design by a structural engineer to show compliance with the building regulations.
The full version of the Trees and Development SPG is available to download:
Note: The above document is in Portable Document Format (PDF) and therefore requires a suitable reader to view it. A reader can be downloaded free from the Adobe website (full instructions for downloading the reader are provided on the site).
More information: