Approaches to Tree Value
CAVAT values the tree stock in terms of their extrapolated and adjusted replacement cost and their relative degree of public amenity. This is related to an approach taken in the United States by the Council of Tree and Landscape Appraisers’ (CTLA), the Trunk Formula method, which has been adapted for the UK by Adam Hollis (Amenity Tree Valuation, Provisional Guidance Note, 2007). However the output of the CTLA Trunk Formula Method is framed in terms of the value of the tree to its owner, whether that might be a private individual or a public authority.
In CAVAT the value of the mature tree is extrapolated from the value of a square centimetre of the cross sectional area at breast height. This in turn has been derived form the average installed cost of a basket of commonly chosen street trees, according to the cost of a square centimetre of stem cross section.
Alternative approaches to tree valuation include measuring the output of the trees either in terms of their visual amenity or their measurable outputs in terms of benefits to the community.
The Helliwell method, developed in the UK, values the visual output of trees. i-Tree, based on work in the 1980’s by the US Forestry Service and subsequently developed, expresses the value of the trees in terms of their carbon sequestration, building energy use reduction, absorption of carbon emissions etc. In i-Tree, trees are given a structural value using either the CTLA trunk formula method or, in the UK, CAVAT.