Planning green infrastructure

When conducting development work or highway improvement works near to trees, it is essential that everyone working on the site adopts all the measures identified to retain trees and minimise damage. It is also essential that all site operatives (site managers, clerks of works, all contractors’ operatives including subcontractors etc.) understand what is needed. 

A meeting should be arranged before work begins with everyone involved to establish good communication and identify all the requirements for retaining trees. Regular meetings and toolbox talks should then take place while the works are ongoing to identify additional requirements and potential problem areas. It is important that all appropriate practices and protection methods are written into contracts, along with penalty clauses which provide an incentive to adopt good practice.

Tree protection measures must be thorough and should be put in place before the works begin and maintained until the works are finished. Inadequate or inappropriate protection measures are a waste of money and can lead to significant damage, which may only become apparent months or years after the works are completed. A damaged or deteriorating tree due to poor site management can present a significant danger to users of the highway and loss of important local amenity and natural capital. 

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Photo of a retained mature tree showing signs of stress and damage New buildings have been erected too close to the existing mature tree which is, leading to health and safety problems in the future.

Figure 38: Retained mature tree showing signs of stress and damage from construction activity. New buildings have been erected too close to the existing mature tree which is, leading to health and safety problems in the future.

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Building so close to retained trees leads to problems with shade and leaf litter. This can result in trees being mutilated and high future maintenance costs.

Figure 39: Building so close to retained trees leads to problems with shade and leaf litter. This can result in trees being mutilated and high future maintenance costs. 

The council’s forestry officer and/or the consultant arboriculturalist should be involved at an early stage so that they advise on retaining existing trees and planting new specimens. The potential growth of retained trees, their future compatibility with new and existing highway features and how near new and existing service runs will be all must be considered. An appropriate protection zone must be provided around trees that are to be retained. All necessary tree maintenance work, both before and after construction, must be carried out by trained operatives in consultation with the council’s forestry officer.

Avoiding damage to trees during construction works

Installing Highway Equipment

When designing and planning highway equipment, consider the location of trees, whether they are on the highway or on nearby property. Care should be taken to avoid installing this equipment within a tree’s potential rooting area and within its crown or potential growing space. Site equipment such as road signs, street lights etc. should be sited to avoid damage to trees during installation and to avoid the need for regular pruning to maintain visibility.

Table 25: The following activities are common causes of damage to trees when construction is carried out within the trees’ natural rooting area.
Excavating trenches

To install and maintain services, for 
foundations, kerbing and so on.

Alterations in soil level

Raising or lowering the soil level.

Installing non-porous surfaces

Affects soil aeration and drainage.

Compacting the surface

By plant, vehicles and storing material.

Soil pollution 

Storing toxic materials (for example, diesel 
oil and road salt).

Physical damage

By plant and machinery to a tree’s roots, 
trunk and branches.

Changes to soil hydrology

 

Caused by changes to drainage which 
accelerates water run-off or compacts the soil which causes waterlogging.

Fires

Burning unwanted material within the tree’s root spread can cause considerable damage to the tree’s roots, trunk and branches.

Exposure

Damage caused by increased levels of sunlight and wind when neighbouring trees are removed.

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Diagram showing the causes of damage to trees during construction works such as soil pollution, bark wounds and soil compaction

Figure 39: Damage to trees during construction works

A tree’s root system can extend radially (outwards) to a distance much greater than the tree’s height. Ideally the whole of this area should be protected and remain undisturbed during construction work.

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