Estimating the economic value of trees at risk from a quarantine disease

The total economic value of tree species susceptible to Phytophthora ramorum, the causative agent of sudden oak death, was investigated in North Yorkshire. The results of a dichotomous-choice contingent-valuation study, using a 'follow-up' dichotomous-choice question, are presented. Two approaches were used in order to obtain the mean willingness to pay (WTP): a bivariate probit model that provides information about the crucial variables that affect the WTP, and the maximization of a log-likelihood function that accounts for a double-bounded bid. Previous studies suggest that the second approach produces more accurate estimates. Using both methods the mean WTP was estimated to be approximately 55 pound per annum per individual taxpayer over five years. This is similar to values placed by the public on trees susceptible to P. ramorum in California, USA.