Graduate Thesis Or Dissertation
 

Comparison of Phellinus weirdi root rot damage in a 60-year-old Douglas-fir (Pseudotsuga menziesii) stand with the damage in the preceding old-growth stand

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  • Laminated root rot of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) caused by the fungus Phellinus weirii (Murr.)Gilbertson was studied in two successive stands in the Oregon Coast Range. Damage due to the disease in a 60-year-old second-growth stand was compared with incidence in the preceding 300-year-old stand on the same site. Information for the comparison was gathered by mapping all current stand trees (living and dead) and the remains of previous stand trees on four one hectare plots. Damage in each stand generation was assessed in terms of the reduction in stand density and basal area by P. weirii caused mortality, the extent of infection among living trees, and the plot area covered by the disease. Current stand damage estimates were based on the amounts and distribution of healthy, infected and dead trees. Live infected trees were diagnosed by the presence of either surface mycelium or internal decay as evidenced by root collar excavation and increment boring of all trees around disease centers. Previous stand damage estimates were based on the number and distribution of infected stumps, snags, and old down trees. Setal hyphae were used as positive evidence of P. weirii decay in old growth residuals. The comparisons of damage revealed that laminated root rot was more destructive in the previous stand at the time of its harvest than in the current second-growth stand. The reduction in stand density by P. weirii caused mortality was greater in the previous stand (75.5%) than in the current stand (41.7%). In the previous stand 60.9% of the trees living at harvest were infected while 35.1% of the living trees were infected in the current stand. The reduction of Expected Basal Area (of a healthy stand on the site) by P. weirii caused mortality was also greater in the previous stand (56.6%) than in the current stand (22.5%). The proportion of the Actual Basal Area infected was also higher in the previous stand (61..8 %) than in the current stand (41.1%). Phellinus weirii was present on 82.5% of the previous stand plot area compared to 51.2% of the current stand plot area. The difference is largely attributable to the larger Area of Concentrated Mortality in the previous stand (68.4% vs. 36.3%). Differences between plots in the Total Area of Infection in the current stand were best related to differences in the type of inoculum from the previous stand and area affected by these inoculum sources (Area of Potential Inoculum). Sixty-five percent of the currently diseased area lay beyond the Area of Potential Inoculum from the previous stand, indicating significant tree to tree spread in the current stand. Although damage levels were higher in the previous stand (at its harvest) than those currently found, the average annual rate of damage increase was much higher in the current stand than the previous stand. Projections of current damage rates to a comparable age predict much higher losses due to the disease in the current stand than were found in the previous stand.
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