Factfiles

Tree Damage in Built up Areas & Development Sites

Damage to the stem and branches

The trunk and branches of trees can be damaged in a number of ways. Damage above ground level is usually caused by the passing of machinery too close to the tree. Fires are also an obvious hazard due to scorching, and an example of a tree prone to scorching is the Beech. Scorching is caused by the removal of existing shade, and can also be caused by reflections of buildings and pavements.

Air Pollution

Air pollution is one main source of damage to the trees of today. The damage is caused mostly from car and lorry fumes. This is also the case in development sites. Looking at their machinery for example, pick up trucks, cement mixers, diggers, work cars, generators and two stoke power engine tools. All these give off harmful gases.

Alteration of water content

Trees can be affected by the improvement of drainage on the development site. This is the lowering of the water table. The water table limits the growth of the roots of most tree species to the soil that lies above the water level. When the water table is lowered, there will be an increase in the area of soil in which the roots can grow. This can be beneficial in the long term.

Water from road surfaces should never be channelled towards trees. This is because the water may be contaminated with road salt or other toxic substances.

Damage in the early stages

Even before work has started on a development site, existing trees can be seriously damaged. If the site is not secure, it is most probable that children will find their way onto the site cause damage. This damage is usually in the way of bark and branch damage. Damage can also occur if fires are lit near to or under trees, and any waste materials that adults dump could be toxic to the tree.

Damage to the root system

It is widely believed that the root system of the tree is not a mirror image of the branches and that there is not usually a tap root. The trees root system is most frequently in 600mm of soil and extends in any direction for distances in excess of the tree’s height. Therefore, it is obvious that when digging foundations on a development site, damaging the trees root structure is probable.

A small tree grown in a nursery can loose up to 75% of its root system and survive relatively unaffected. On the other hand, a fully mature tree can show die back if as little as 5-10% of its root system is lost. A healthy tree growing strong can loose up to 30% of its root system without showing any signs of die back. This may be true, but when you create a problem, it usually leads to others. For example, if you cut 50% of a tree’s root structure away, the tree will become unstable. Also, any loss of roots will lead to the possibility of attack from pests and diseases.

The bark on the root can also be damaged. The bark protects the roots from decay, therefore, this can cause problems. If the bark beyond this point is damaged all the way round, then the root beyond this point will die. The root system can also be damaged by soil compaction, which is caused by heavy objects being stored near to the tree. Also, soil compaction can be caused by heavy machinery being constantly driven over the tree’s root system. The result of this restricts gaseous diffusion within the soil, and asphyxiates the tree’s roots. The root system of a tree must have oxygen to survive, otherwise the implications are disastrous. Damage can also occur by Tarmac layering, water drainage and the incorrect use of herbicides.

Subsidence

Trees that are planted near to buildings on clay soil will eventually start removing large amounts of water. By the tree doing this, the soil will begin to shrink risking possible building subsidence. This would not occur if the tree was there before the building.

Heave

If a well established tree near to an existing building is felled, it will lead to the destruction of the root structure. Once the roots are dead they can not absorb any water any more. This causes an increase of water in the soil which eventually swell, causing damage to the building. This is also a problem when large woodlands are felled to make way for development sites. This is because it can take several years for the soil to fully expand again. However, heave is only a problem on clay soils.

Mechanical Damage

The foundations of buildings can sometimes be damaged by the direct contact of a tree’s root system.

Windsway Damage

If a building is built too close to a tree, then the implications can be disastrous. Basically, the roots of the tree may grow right underneath the foundations of the building. If this happens as the tree sways in the wind, the roots move upwards inflicting damage to the foundations.

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