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PiCUS Sonic Tomograph (Victoria Park, Rangiora)

Purearb was engaged by Warner Tree Care Limited on behalf of the Waimakariri District Council to assess the condition of one Council owned Weeping ash (Fraxinus excelsior 'Pendula') within Victoria Park, Rangiora.

This report aimed to provide an assessment to determine internal structural condition using ultrasound testing to one planting of Weeping ash, to enable recommendations and potential options for the ongoing management of the tree. The provided information was reviewed in conjunction with the Warner Tree Care, tree condition survey to enable the Council to make an informed decision and to exercise judgement for the management of the tree.

The assessment height was selected following an initial climbing inspection, indicated a cavity opening filled with cement, highlighted concern with the tree's proximity to the picnic area to warrant a further investigation. The tree's circumference (205cm) and geometry of the measuring level determined the number and location of measuring points. Sensor measuring point 1 was set at North, and the subsequent 9 sensors were spaced strategically around the circumference of the tree, creating a horizontal plane.

The concrete (barrier) identified, may effectively impede linear propagation of the acoustic waves, causing faulty interpretations to lead to erroneous tomograms, that may create results which do not reflect the correct composition of the wood. Therefore, the chosen tomogram measuring level was taken at approximately 220 centimetres to determine observable partially altered wood in different stages of decomposition, starting with early stages of (incipient) decay (leading to a correspondingly small change in density) and degraded wood structure to the main bifurcation junction.


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