In the course of reading a resource consent application for a tree removal recently, I came across the standard accepted method for assessing the value of trees in order to work out the cost of mitigation (i.e. what new trees or other plantings will be planted) in dollar terms. Having a professional interest in such things – I am a business broker as well as an elected member of Council – I am setting out the approach in this post.
Removal Costs are based on the current costs of tree removal incurred by Council including the physical removal of the tree and stump.
The following formula is used to assist with calculating the monetary amenity value of a tree.
Value (V) = Basic Value ($) x Species (S) x Aesthetics (A) x Locality (L) x Condition (C)
When young trees with less than a 6cm trunk diameter or less will be replaced by another tree, there will be no amenity value charge. The Auckland method is based on the method used by the City of Melbourne which was derived from the formula (by Dr. Peter Yau, 1990) of the Maurer-Hoffman Formula.
The basic monetary value of a tree is taken from the internationally accepted table of values devised by the American Council of Tree and Landscape Appraisers and the International Society of Arboriculture, which in the base year 1988 was US$27 per square inch basal trunk area. When converted to a value corresponding to centimetres in trunk diameter at breast height (DBH) the Basic Monetary Value table has been updated to reflect more current monetary values.
Basic Value ($) is determined by matching the trunk diameter at breast height (DBH) with its corresponding base value:
Species Factor (S)
A tree is assessed according to its known natural life span and its rate of growth in a particular environment. For example, a long-lived tree will be scored higher than a short-lived tree. significant features of the tree will also modify how the tree is scored. Judgement regarding species factor must be made by a qualified arborist.
The aesthetic value of a tree is determined by the impact on the landscape if the were removed. This category is closely tied to the locality factor (L).
The locality factor is determined by the tree’s geographical situation. Trees in a large city main street or boulevard score highest because of the stressful growing environment in which the tree has to survive. As the location becomes more rural, the significance of the tree diminishes.
Tree Condition (C)
The tree condition value is determined by the corresponding total score of the assessment criteria.