Protection of retained trees during development

Trees are often overlooked during development and as a result many are either lost or given inadequate protection that results in their demise within a few years. In 2005 the British Standard BS 5837 Trees in relation to construction - recommendations was released and this is now considered the benchmark document for how to successfully retain suitable trees in proximity to development.

Trees have to adapt to their immediate surroundings and any changes will have some effect therefore it is essential that a detailed tree survey that complies with the British Standard is undertaken before a scheme is designed.  This will schedule the trees according to their suitability for retention and identify the extent of land required to ensure that they have the best chance of survival. Older trees are more vulnerable and they are often the most desirable to retain for both their amenity and conservation value.

Common damage to trees during development

• abrasion of bark and wounds that leave wood tissue exposed
• crushing of roots be vehicles / plant equipment and / or storage of materials
• severing and removal of roots by excavation
• broken branches leaving wood tissues exposed
• poor pruning
• fire damage
• poisoning of roots from spillage or storage of fuel, oil, chemicals etc 
• changes in soil levels around trees resulting in root death
• installation of impermeable surfaces

The part of the tree most susceptible to damage is the root system because:

• roots cannot be seen and their extent is not realized

• of a lack of understanding of root function and their importance for the health of the tree

The effects of damage can be serious but often it takes several years for this to become evident and is not always linked back to the cause -  damage during development work. Often by the time the damage becomes evident the developer may no longer own the site leaving the new owner with the problem and the potential need for costly tree work.

Lack of protection can also result in damage to bark and branches that can disfigure a tree and result in disease and decay that also reduce safe life expectancy.

Tree Root Systems

Roots have three main functions:

• absorption of water, oxygen and nutrients

• tree ‘food’ storage in the form of starch

• structural support

Tree root development is entirely opportunistic and spreads horizontally to a distance and depth entirely dependent upon the ground conditions encountered. Very few trees have a 'tap root' after the first few years. Roots require oxygen and water to function and therefore most will remain close to the surface,  research has shown that 90% of tree roots are to be found in the top 600mm of soil. Roots may extend horizontally for considerable distances and where conditions are suitable this distance may be equivalent to two or even three times the tree height.

The majority of roots are the easily overlooked fine, fibrous roots that absorb water, oxygen and nutrients from the soil; these are easily damaged by crushing and removal during soil stripping operations. The main structural support roots are usually found within a few metres of the tree stem and these are linked to the fibrous roots by a network of cable like roots that also provide additional anchorage.

All tree roots are important. 

Prevention of Damage

The guidance contained within BS 5837 Trees in relation to construction – recommendations identifies a Root Protection Area (RPA) based on the stem diameter but protective measures may need to be increased to the extent of the branch spread to avoid damage to the above ground parts of the tree. Tree protective measures are detailed within section 9 of  BS 5837 Trees in relation to construction – recommendations (see right) but as an alternative to weldmesh panels, 20mm exterior grade ply or other robust boarding can be securely attached to the framework.

It may be necessary to carry out temporary work within the Root Protection Area especially on a small or difficult site, for example the erection of scaffolding. The diagram below should be used for guidance.

Further information on tree protection can be obtained from:

• Contact: Rob Sim (Arboriculturist) on Thursdays and Fridays only
• Address: Eden District Council, Planning Policy, Department of Communities, Mansion House, Penrith, Cumbria, CA11 7YG
• Telephone: (01768) 212159
• Email: rob.sim@eden.gov.uk
• Fax: (01768) 890732