An overriding management goal for national parks is the maintenance or, where necessary, the restoration of natural ecological processes. In Sequoia-Kings Canyon and Yosemite National Parks, there is concern about the effects of fire suppression on the giant sequoia-mixed conifer forest ecosystem. The National Park Service is currently using prescribed fire management and prescribed burning as tools to reintroduce fire as a natural process. However, there are questions about the positive and negative effects of reintroducing fire in the giant sequoia-mixed conifer ecosystem.Reintroducing fire in the Sierra Nevada forests needs critical evaluation with respect to the pathogens that affect giant sequoias. We designed a 3-year study, funded by the U.S. Department of the Interior, National Park Service, to: (1) determine the effects of fire scars and their re-burning on the incidence, extent, and survival of fungi in giant sequoia; (2) identify pathogens, insects, location of decay, and other characteristics present in standing old-growth giant sequoia fire scars; (3) evaluate host specialization and cross infectivity of isolates of Heterobasidion annosum from white fir (Abies concolor), red fir (Abies magnifica), and giant sequoia (Sequoia gigantea); and (4) develop criteria and recommendations for monitoring the effects of fire on pathogens in giant sequoia stands.The total circumference of giant sequoia trees affected by fire scars ranged from 3.3% to 69.5%. Cross-sectional area affected by fire scars ranged from 3.2% to 53.7%. The season of year in which prescribed burning takes place could influence the effect fire has on giant sequoia. A survey of 90 fire scars for the presence of resin, Mycocalicium, carpenter ants, other insects, Arachnids, decay above and below groundline, and bird activity (i.e., cavities) yielded a high presence of each factor when all burn groups were combined. Statistically significant differences in bird cavity activity, decay above groundline, and carpenter ant activity were noted among the unburned group, 1-year burn group, and 5-year burn group. The Pilodyn wood tester was effective in determining the presence of decay above and below groundline. A variety of microfungi were found associated with giant sequoia fire scars. The fungi most frequently isolated were: Byssochlamys fulva from 34 out of 90 fire scars (38%), Acrodontium intermissum from 22 out of 90 fire scars (24%), and Tritirachium sp. from 14 out of 90 fire scars (16%). Several other microfungi and Basidiomycetes were also identified. H. annosum acts as both a saprophyte and a pathogen in the giant sequoia-mixed conifer ecosystem. The results of these experiments have demonstrated H. annosum can spread from true fir to giant sequoia and vice versa, given that they are of the same 'S' intersterility group. © 1998, Tall Timbers Research, Inc. Abstract reproduced by permission.