Bridgeoporus nobilissimus is much more abundant than indicated by the presence of basidiocarps in forest stands

Abstract

The polypore Bridgeoporus nobilissimus produces large perennial basidiocarps on large diameter Abies stumps, snags and trees in coniferous forests of the Pacific Northwest. Despite the size and persistence of the basidiocarps, they are rarely observed, making the conservation of this species a concern. We determined that a genetic marker for this fungus could be detected in DNA extracted from wood cores taken from trees hosting basidiocarps. We then tested 105 trees and stumps that did not host B. nobilissimus basidiocarps in plots surrounding B. nobilissimus conks, and 291 trees and stumps in randomly located plots in four stands that contained at least one B. nobilissimus basidiocarp. We found that trees of all sizes throughout all of the stands hosted B. nobilissimus . The proportion of Abies trees (live and dead) colonized by B. nobilissimus in these stands ranged from .06 ± .04 in a recently thinned stand to .39 ± .08 in an old growth stand. The spatial density of B. nobilissimus colonized trees ranged from 25 ± 13 to 61 ± 12 trees/ ha. The spatial density was highest in the old growth stand, but intermediate in the recently thinned stand. In a separate study we detected B. nobilissimus DNA in three conifer species that were not known to host this species: Pseudotsuga menziesii , Tsuga heterophylla , and Thuja plicata . Our results indicate that the survival strategy of this fungus is to produce and maintain a mycelial presence in its hosts while infrequently producing a long-lasting basidiocarp. The detection of B. nobilissimus , and other fungi adopting this reproductive strategy, is difficult using visual observation, but achievable using methods based on DNA detection of mycelia in hosts.