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Trees can live for a long time but eventually die, either from natural causes or killed by man. Ill-health of trees can be diagnosed, and early treatment, pruning or felling to prevent the spread may result in timber stocks and amenity trees being saved. Arborists/arboriculturists need to be aware of the risk posed by hazardous trees. Construction projects sometimes avoidably damage trees. ==Sources of tree damage== The causes of tree damage and abnormalities can conveniently be divided into either biotic (from living sources) or abiotic (from non-living sources).〔Strouts, R. G. and Winter, T. G., Diagnosis of ill-health in trees, Research for Amenity Trees No. 2 1994〕 Biotic sources include insects (e.g. that bore into the tree), mammals (e.g. deer that rub bark off), fungi, birds, nematodes, bacteria and viroids.〔Wiseman, P. Eric, Integrated Pest Management Tactics, Continuing Education Unit, International Arboricultural Society Vol 17, Unit 1, February 2008〕 Abiotic sources include lightning, vehicles impacts, construction activities, drought, waterlogging, frost, winds, chemicals in the soil and air and soil nutrient deficiencies. Construction activities can involve any of a number of damage types, including grade changes or compaction that prevent aeration to roots, spills involving toxic chemicals such as cement or petroleum products, or severing of branches or roots. Any of these damage sources and the natural ageing of trees may result in trees or parts of them failing prematurely. The term "hazard trees" is commonly used by arborists/arboriculturists, and industry groups such as power line operators, for trees that, due to disease or other factors, are more susceptible to falling in windstorms, or having parts of the tree fall. Damage may also disfigure amenity trees, create unacceptable risks to people, reduce the safe useful life of trees or reduce the value of commercial timber. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tree health」の詳細全文を読む スポンサード リンク
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