FIELD GUIDE FOR VISUAL TREE ASSESSMENT (VTA)

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Abstract
The VTA-Method (VISUAL TREE ASSESSMENT) consists in three steps. Visual control of the tree in order to find external symptoms of internal defects. If the constant stress distribution in a tree is disturbed due to the presence of a defect the tree attaches more wood at the overloaded spot. So bulges or dents are formed near decayed hollows and ribs near cracks etc. If symptoms are detected the related defect has to be confirmed and measured by deeper inspection. This can be done by measuring the velocity of a sound wave traveling through the cross-section and by drilling methods. The strength of the remaining healthy wood is determined now with the FRACTOMETER, a wood testing device in pocket-size. If defect size and wood quality is known failure criteria are used to decide whether the tree is dangerous or not. VTA is nondestructive for healthy trees. Only if there is a reason for increasing concern the tree is subject of deeper inspection but also in this case the wounding of the tree has to be kept minimum.

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