Harmon, Mark E. 1989. Effects of bark fragmentation on plant succession on conifer logs in the Picea - Tsuga forests of Olympic National Park, Washington. American Midland Naturalist. 121: 112-124.
Plant succession on Picea (spruce), Pseudotsuga (Douglas fir) and Tsuga(hemlock) logs in the Hoh Rain Forest, Washington, was examined using the chronosequencemethod. Bark fragmentation patterns differed among these species; Picea and Tsuga logs losttheir bark in 60 years and Pseudotsuga in 190 years. Bark of logs of all species was 85-90%covered by bryophytes within 11-19 years after tree fall. Live and dead bryophytes reachedsteady-state masses on bark of 324 and 684 g/m2 within 91 and 150 years, respectively.Humus mass on bark of logs of all three species increased slowly the first decade and rapidlyafter 20 years; a steady-state humus mass of 4400 g/m2 was predicted after 190 years. Treedensity on bark peaked at 140/m2 at 15-25 years and then thinned at a rate of 8%/yr. Barkfragmentation influenced succession by removing plants and reinitiated the sere. Modelingindicates differences in succession patterns among species of logs were caused by differencesin bark fragmentation patterns. Although logs are a major seedbed in Picea-Tsuga forests,self-thinning, bark fragmentation and toppling of trees greatly reduced long-term survivalon logs.