CAVAT (Capital Asset Value for Amenity Trees) has become popular for appraising urban trees in the UK. It is one of several approaches to addressing amenity value. Each has its problems. Expert-driven approaches may be subjective and unrepresentative. Consumerbased approaches remain susceptible to expert biasing and incentives to overstate values (stated preference approaches), or inappropriate modelling of valuation (hedonic pricing). Cost-based approaches use objectively quantified sums of money, but it is problematic to relate these costs to resultant benefits. CAVAT’s unit value factor, per square centimetre of basal area, is derived by dividing the cost of planting an amenity tree by the basal area it has at planting time. This is scaled up to the basal area of the tree being assessed. Further adjustments are made for particular aesthetic characteristics, the number of beneficiaries, and the life expectancy of the assessed tree. The fundamental problem, in treating the unit value factor as a measure of benefit, is that it is set as though planted trees are not expected to grow further, but is then applied to trees that have grown further. This leads to size being double counted. Taking rational and explicit account of tree growth in setting a base value gives tree values only about 3% of CAVAT’s value, or even less. Major modification of CAVAT is needed before
