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:
