Street tree valuation systems

Street trees and urban woodlands provide a number of environmental and social benefits, including contributing to climate change adaptation and mitigation and providing urban green space. This Note presents the results of a review of three approaches to estimating the amenity value of street trees: CAVAT, Helliwell and i-Tree. The review showed that the three valuation systems differ significantly in methodology, data requirements and outputs. At one end of the spectrum the Helliwell system is entirely based on expert judgement, focuses solely on visual amenity value and has very low field data requirements. At the opposite end of the spectrum i-Tree requires data collected from a sample or a complete inventory of the street tree population as well as community-specific information (e.g. programme management costs, city population size, and price of residential electricity) to output customised benefit and cost data. CAVAT falls somewhere in between, focusing on wider benefits of trees to communities rather than purely visual amenity, but not outputting detailed benefit and cost data. The CAVAT and i-Tree systems can meet the needs of both small communities and large metropolitan areas. However, if limitations on data availability can be overcome, i-Tree offers significant advantages of flexibility, detailed output and permits a wide range of benefits to be assessed. The Helliwell system seems best targeted to single tree and small-scale community evaluations, but can also handle urban woodlands. Research Note