Application of tree visual assessment for failure and health evaluation - a case study of aged trees in Taichung City and County.
Chan MingHsun, Wang YaNan, Kao YuChien, Chen JinHau, Lin Chinsu, Hsiao WenWei
Author Affiliation: Experiment Forest, College of Bio-resources and Agriculture, National Taiwan University, Taipei, Taiwan.
Journal of the Experimental Forest of National Taiwan University 20 : 99-116
Abstract : Aged or shade trees belong to public facilities. Management of these trees is closely related to the people's life, health and property. Managers of these trees are responsible to ensure the safety of pedestrians, since these trees pose a potential risk for the pedestrians. In addition, possible damages to properties of the third party by the falling of aged or shade trees compose liability for those tree managers. However, those taking care of shade trees do not understand the technical standards and thereby log and trim trees arbitrarily. This paper employs tree visual assessment to evaluate aged or shade trees in Taichung city (Taiwan) and offers technical standards for judging the danger and health of aged or shade trees. This technique is a non-destructive evaluation and is composed of two procedures: surface assessment and accurate examination. Surface assessment includes the gesture and shape of trees, the extending length of branches, the damage of the edge of branches, thickness of leaves and the degree of aging of the barks. The degree of aging can be classified into five types: better 0.8, slightly worse 0.8-1.6, worse 1.6-2.4, significantly worse 2.4-3.2 and immediately dying 3.2. According to the degree of decay, accurate examination is ranked into four levels: the first level 25%, the second level 26-50%, the third level 51-75%, the fourth level 76-100%. A comprehensive evaluation based on the degree of decay and health is divided into four levels: healthy, noticeable, significantly noticeable and dangerous. According to the surface assessment, four are significantly worse of the third level of decay; nine are worse of the second level of decay and three are slightly worse of the first level of decay. As far as the accurate examination of trunk decay is concerned, one is in the second and third level and 14 are in the first level. Judging from the comprehensive evaluation of tree visual assessment, three aged trees are in healthy condition, two are in noticeable condition, and two mangoes are in substantial condition. None is in the dangerous condition. It is notable that the two mangoes might break because of the decayed trunk over the threshold (30%).