Estimating the susceptibility to Phytophthora alni globally using both statistical analyses and expert knowledge

Abstract

Phytophthora alni subspecies alni Brasier and S.A. Kirk is a recently hybridized soil and waterborne pathogen causing root and collar rot of species of the genus Alnus spp. (alder). It has quickly spread throughout Europe via planting of infested nursery stock and irrigating fields with infested river water. Once introduced, the pathogen spreads naturally by means of streams, floods, and other drainage water. Phytophthora alni can also be passively transported with the bare-root nursery stock, as it is able to adhere to and infect fine roots of visually symptomless plants of alder and other tree species exposed to the pathogen. We used a classification tree on 434 infested and healthy sample points to determine the required conditions for P. alni to successfully infest a nonflooded forest site. Sample points had been collected from 2003 through 2006, and a potential distribution surface was created for forested areas in Bavaria. A tenfold cross-validation accuracy of 78 percent was attained. To understand the potential hazard posed by P. alni elsewhere in the world, the rules from the Bavarian classification tree were applied along with additional expert knowledge in a multicriteria model to create a global susceptibility surface for P. alni.

Parent Publication

• Advances in threat assessment and their application to forest and rangeland management—Volume 1 and Volume 2.

Citation

Downing, Marla C.; Jung, Thomas; Thomas, Vernon; Blaschke, Markus; Tuffly, Michael F.; Reich, Robin. 2010. Estimating the susceptibility to Phytophthora alni globally using both statistical analyses and expert knowledge. In: Pye, John M.; Rauscher, H. Michael; Sands, Yasmeen; Lee, Danny C.; Beatty, Jerome S., tech. eds. Advances in threat assessment and their application to forest and rangeland management. Gen. Tech. Rep. PNW-GTR-802. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest and Southern Research Stations: 559-570.