Phellinus weirii

Abstract: Mountain hemlock forests in the Oregon Cascades exhibit wave-form dieback resulting from infection by laminated root rot (Phellinus weiril). Although Phellinus remains viable in dead roots after the wave of dieback passes, many regenerating mountain hemlock forests do not become immediately reinfected. We measured at least a doubling of nitrogen availability in the dieback and regrowth zones, and thought that this increased availability could improve tree resistance to the fungus. To test this hypothesis, we grew small mountain hemlocks under nutrient and light limitations in a growth room, and then inoculated them with the fungus. Trees growing without added nutrients had significantly greater foliage damage and mortality after Phellinus inoculation than did trees growing with nutrients. Shading significantly increased susceptibility whether or not nutrients were added. We believe that increased nitrogen availability and possibly increased light levels after dieback in the field act similarly to increase resistance and prevent reinfection of the regrowing stands. Foliage damage and susceptibility to infection were related to pool sizes of total nitrogen, phos- phorus, and nonstructural carbohydrates. Plants with very low nitrogen reserves (< 10 mg per plant), or very low energy reserves (< 20 mg starch per plant), were more susceptible. It appears that resistance to Phellinus occurs via a defensive pathway that requires resources of both nutrients and carbohydrates.

Abstract: Because Pseudotsuga menziesii (Douglas fir), an early seral dominant in western Oregon forests, is particularly susceptible to the pathogenic root rot caused by the fungus Phellinus weirii, it was hypothesized that successional development in affected forests would be accelerated. The basal area of late successional tree species and common shrubs were compared inside and outside Phellinus weirii“infection centers”. Future successional impacts indirectly caused by disease presence were assessed by comparing the abundance of regenerating tree species inside and outside of these centers. Results for old-growth sites in the lower Cascades supported the initial hypothesis. The presence of Phellinus weirii at these sites appears to push changes in the late successional species basal area along the same trajectory. At the Coast Range sites, however, shrub growth was greatly enhanced rather than the growth of Tsuga heterophylla (western hemlock), the only late successional tree species at these sites. Regeneration of trees was sparse in all areas and was negatively correlated with the basal area of existing western hemlock, and not directly correlated with the presence of the pathogen. However, because the basal area of western hemlock is influenced by the presence of disease in the Cascade sites, Phellinus weirii may be an influential indirect factor in the future successional direction of the sites. This study demonstrates the potential importance of native pathogens in determining the successional status of a community, as well as the importance of such biotic agents in the physical structure of multi-strata forested communities as a whole.

Abstract: The forests of western North America are affected by root diseases caused by several endemic fungi. These have both important economical and ecological impacts. Phellinus weirii (laminated root rot) is particularly important in coastal Douglas fir forests. Forest managers would like to know the location of pockets of Phellinus weirii infected trees for the purpose of salvage, remedial activities and inventory. Airborne multi-spectral imagers, coupled with automated detection of damaged trees have potential to provide a cost-effective survey method. Two sets of Compact Airborne Spectrographic Imager (CASI) airborne multi-spectral imagery were acquired at 60 cm resolution over the same Douglas fir dominated site in coastal British Columbia, Canada. They were acquired in successive years and radiometric corrections for the effects of illumination and view angle applied. Trees of varying levels of root rot symptoms were assessed in the field and manually delineated on the imagery. Spectral properties of these...