Trees are woody plants with a trunk. Shrubs are also woody but have no trunk with the branches more or less at ground level. It is easy to distinguish the two as trees have a crown at the top and shrubs have a crown closer to the bottom.
There are many types of trees: large and small, stout and slender, erect and weeping and evergreen and deciduous. Over the centuries of cultivation and with propagation we now have a great assortment of trees offering considerable choice for landscapers, park planners and the gardening home owner.
Trees are usually quite distinguishable from one another even during the winter when they can be recognised by their bark, twigs and branches. No one tree is the same as another even if it is the same species. Their rate of growth, shape and ultimate size will all be determined by their position and climatic environment.
The changing seasons are reflected by the leafy and leafless phases in the life of the deciduous tree. In the spring, as the weather gets warmer, new sets of leaves grow covering the tree with bright green foliage. During the summer the leaves absorb and use the energy of sunlight to produce organic food materials; this process is known as photosynthesis. Each leaf contains the substance chlorophyll and with light energy makes chemical substances which are retained and can be released as energy for growth or to build up the tree. Carbon dioxide which is present in the atmosphere is combined with water absorbed by the roots to form energy rich sugars. Together with mineral salts, which the roots absorb, an intricate chemical process takes place and forms the trees substance, i.e. wood, roots, seeds, and leaves.
In the Autumn the leaves provide mobile food material. They change colour from green through to orange and then, after their work is done, they fall from the branches, leaving behind them small leaf scars. At this stage the tree has already made preparations for the new leaf growth. On the ground, the fallen leaves decay and produce a rich mineral nutrient mould which feeds the trees roots.
Evergreen trees have a longer life cycle. Each leaf lasts for several years. Each year new ones are added and a few of the older ones fall but the tree never becomes leafless.
This growing process produces a cycle of moisture demand from the ground, greater in the summer and less in the winter, and on clay this alters the volume of the ground and can cause subsidence.
BALANCE .. TREES AND PROPERTY
Beautiful though they may be it is necessary to make sure that trees on your land (and your neighbour’s) contribute to the environment without damaging properties. Leafy suburbs, residential tree-lined avenues and wooded gardens are a inherent and integral part of our “green and pleasant” land. But beware the dangers!
Large trees spread out and their roots can quickly become entangled with house foundations. Worse still – a tree’s search for water can suck moisture from the ground leaving clay soils shrinking. This causes a lack of support to a property’s foundations and can lead to subsidence.
A mature deciduous tree can draw up to 50,000 litres of water a year from the surrounding soil. Biggest culprits are Willows. They look great but the best place for them is at the bottom of the garden – at least 11m from your house. Other large water users are Poplars, Elms, Oaks, Horse Chestnuts, Planes and Ash. Among those that can be planted nearer to your home – but not too near! – are Magnolia, Yew, Holly, Laurel, Spruce and Pine.
Keeping the problem of a trees location in the relationship to a building in perspective is very important. Leafy suburbs, residential tree lined avenues and wooded gardens are an inherent and integral part of our environment. In both town and country they enhance the amenity and give colour and form with the passing of the seasons. However, the eventual size, species and location should be taken into consideration
Inappropriate species planted near to building should be avoided. The right tree for the right place should be the balance which we look for. Even if a tree is close to a building it may not necessarily cause a problem. There are, for instance, many thousands of oak trees within 8 metres that have existed for many decades and do not cause such damage. We should never jump to any conclusion that trees are always the culprit for a building’s ills. The age and method of construction and the way it has been maintained are of equal importance.
The wisdom of retaining a particular species, together with the overall tree health should be considered where trees are particularly abundant or close to the property of a certain age. Many arboriculturalists will have received training in the methods to advise you on these matters.
TREES TOO LARGE … AND TOO CLOSE
There are no hard and fast rules of assessing the risk of damage that tree growth close to a building will do. Because of the immense number of variable factors that take place in the process, making predictions is fraught with difficulty.
This is where the application of a little common sense is called for! If there are large trees near your house, and by large we mean over 8 metres (26 ft.) and by near we mean 10 metres (33 ft.) serious consideration should be given to regular pruning particularly if you live in an area where there are clay subsoils.
Our best advice is to always seek site specific advice in the first instance by reference to your local authority tree officer, or a qualified and experienced arboriculturalist, particularly if your neighbourhood is in a conservation area. By pruning regularly not only will the aesthetic shape of the tree be maintained but by restricting the leaf growth you will also restrict root spread and moisture demand.
Always remember that even if your house is affected by tree growth desiccation, the degree of damage is usually very small and is more likely to be unsightly rather than structurally unsound.
Did you know?
Preliminary research by the Building Research Establishment suggests:
- Detached properties have a greater susceptibility to subsidence or heave damage than non-detached
- Properties built prior to 1900 are less susceptible to damage than those built thereafter
London clay is, by far, the most commonly encountered “problem” soil.
- It typically takes about 50 years between construction and the onset of damage, while only about 6% of cases occurred in the first 10 years after construction.
- The likelihood of a property being underpinned following damage generally increases with the level of damage
Oak trees are, by far, the most damaging species of tree.
TREES IN COUNCIL OWNERSHIP
Avenue and street trees that are owned and maintained by the Local Authority have usually been chosen for their particular qualities: slower growing varieties requiring less maintenance or pruning are more appropriate to the street scene and have been fashionable for more than 50 years with the advent of the Town and Country Planning Act.
Before then developers and owners alike planted grand avenues of plane, poplar and elms. Alas many of the elms have succumbed to disease but the planes and poplars have now reached maturity. Plane especially can be cut back well without difficulty or serious harm to the tree. Most local authorities are aware of the relationship between trees and property and the risk of subsidence related damage that can occur.
The specific responsibility for the maintenance of the trees varies from authority to authority. If you think that a local authority tree is causing damage you should contact your authority’s Tree Officer or Parks Department and seek their advice, but remember only if there are clear indications that damage is occurring. Suspicion that it may cause a problem is not sufficient. Some of the tell-tale signs to look for are:
- Diagonal cracks wider at one end than the other appearing in the walls around the doors and windows, both inside and out (fig.1).
- Are the cracks wider than 5mm?
- Are any doors or windows sticking?
- Cracks around bay windows
- Floors beginning to slope (Fig. 2).
Call us on 07596 695651 or 07770 598 712
Subsidence Claims Advisory Bureau
9 Clevedon Road, Bexhill on Sea, East Sussex