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WHAT ARE TREES? |
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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, with the 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. |
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BALANCE .. TREES AND PROPERTY |
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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. |
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TREES TOO LARGE ... AND TOO CLOSE |
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| 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 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. |
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TREES IN COUNCIL OWNERSHIP |
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| 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 telltale signs to look for are: |
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| Isolated cracks in ceilings or at the junction of walls and ceilings are not likely to be indications of tree subsidence. | ||||
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Fig. 1 |
Fig.2 |
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