Mapping Sudden Oak Death Risk Nationally Using Host, Climate, and Pathways Data

In 2002, a team of United States Department of Agriculture-Forest Service (USDA-FS) scientists developed a preliminary risk map to serve as the foundation for an efficient, costeffective sample design for the national sudden oak death detection survey. At the time, a need to initiate rapid detection in the face of limited information on Phytophthora ramorum necessitated a simple spatial intersection of factors traditionally used in risk mapping: (1) distribution of hosts known or likely to be susceptible to the pathogen, (2) climatic conditions adequate for survival and propagation of the pathogen, and (3) pathways for introduction of the disease outside the currently infected region. The resulting map consisted of hexagons indicating three ordinal levels of risk (high, moderate, low) covering the conterminous U.S. Beyond aiding prioritization of sampling effort, the map has facilitated the dissemination of information about the potential threat of the disease to the public. However, additional information about the pathogen has emerged in the last few years, so we created a new map by incorporating current data and approaches to better depict principal factors of P. ramorum risk. The new risk map will be used to improve sampling procedures for detecting the pathogen’s potential movement into wildland areas. In addition, it will serve as the basis for analysis of the potential economic costs if P. ramorum were to become established in eastern U.S. forests.