Characteristics and consequences of root diseases in forests of Western North AmericaAuthor(s): D.J. Goheen; W.J. Otrosina
Source: In: Frankel, Susan J., tech. coord. User’s guide to the western root disease model, version 3.0. Gen. Tech. Rep. PSW-GTR 165. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Station: 3-8.
Publication Series: Miscellaneous Publication
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DescriptionRoot diseases are somewhat mysterious. Operating as they do within the soil, it is difficult to actually view root pathogens or follow their progress in causing disease. The signs and symptoms that they produce can be quite subtle and variable. Just identifying which pathogen occurs in a specific situation is often challenging. Nevertheless, in the past two decades, forest managers have become increasingly aware of the important roles that root disease organisms play in forests and the significant influences that they exert on the ability to attain desired management objectives. Root pathogens usually affect groups of neighboring trees in progressively expanding disease pockets or centers. These centers generally contain dead trees that have died at different times over several years and living but infected trees in various stages of decline. They are commonly characterized by much lower stocking levels than surrounding healthy portions of stands, and they also may contain numerous windthrown or broken trees on the ground. Root disease centers vary in size from those involving only a few trees to those covering hundreds of acres. They may be very discrete or they may involve a scattering of affected trees dispersed over a larger area.
On individual trees, crown symptoms associated with most root diseases are similar and include reduced height growth, loss of needles, chlorotic foliage, death of branches, production of distressed cone crops, and, ultimately, host mortality. Accurate identification of which root pathogen or pathogens occur in an area usually requires digging to expose roots, and removing bark from roots and root collars to reveal the inner wood. Often laboratory culturing or more sophisticated techniques such as isozyme and DNA analyses are necessary to identify the biological species or strain of the causal fungi. Although a number of root diseases are found in the West, three are considered to be the most significant. These are laminated root rot, caused by the fungus Phellinus weirii; Armillaria root disease, caused by Armillaria ostoyae; and Annosus root disease, caused by Heterobasidion annosum. The impacts of these fungi on forest stands are modelled in the Western Root Disease Model, Version 3.0. A general understanding of their biology is presented to enhance the reader's ability to input data and interpret outputs.
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CitationGoheen, D.J.; Otrosina, W.J. 1998. Characteristics and consequences of root diseases in forests of Western North America. In: Frankel, Susan J., tech. coord. User’s guide to the western root disease model, version 3.0. Gen. Tech. Rep. PSW-GTR 165. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Station: 3-8.
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