The following information is from Spies et al. (1988). See Spies et al. (1988) for more detail about sample design and methods, and for a map of study sites. Note* This data is applicable to all of the WLCH Wildlife Habitat Types and all the S-Classes therewith.
The Old Growth Study was conducted in Douglas-fir-dominated forests in Washington and Oregon in three physiographic provinces: southern Washington Cascade Range, western Cascade Range of Oregon, and southern half of the Oregon Coast Range. The study area encompassed the western hemlock vegetation zone, the lower elevational portion of the Pacific silver fir zone, the northern margin of the mixed-conifer zone in southern Oregon, and the eastern margin of the Sitka spruce zone in the Oregon Coast Range. A total of 196 stands representing different ages (40 to 900 years) and site conditions were sampled in 1983 and 1984. All stands originated after wildfires that killed all or nearly all of the overstory trees. The stands had not been disturbed by roads, harvesting, or other forest management activities. Sampled stands were classified as young (< 80 yr), mature (80-199 yr), or old growth (> 200 yr)
Stand size ranged from about 4 to 20 ha. Within each stand, five nested circular plots were established systematically at 100 or 150 m apart. Each set of nested plots consisted of a 0.05-ha plot for down wood, a 0.1-ha plot for all snags, and a 0.2-ha plot for snags >50 cm dbh and >15 m tall.
All down wood >10 cm diameter (large end) that projected into the plot were measured. Data recorded included length (within the plot), horizontal diameter at both ends, species, and decay class. All snags >0.1 m tall with upper diameters >10 cm (10 cm dbh for snags >1.4 m tall) were measured in the 0.1-ha plot and recorded by species, dbh, height, and decay class.
The volume and number of logs and snags and the projected area of logs were computed by species and decay class for each plot in the stand. Volume was computed using the formula for a cone. Stand values were then calculated from the means of the plot values.
For comparing to the DecAID wildlife and inventory summaries, we considered all Old Growth Study plots to be in westside conifer hardwood forest. The physiographic provinces used in the Old Growth Study were the same as the subregions used in DecAID, except no Old Growth Study data were available for the Washington Coast Range. We assumed that the “young” stands of the Old Growth Study fell within the “mid-successional” category used in DecAID, and that both “mature” and “old growth” stands fell within “late-successional.” For DecAID, we used the estimates of down wood cover published in Spies et al. (1988, Table 3, p. 1694). For estimates of snag density, we obtained the original snag data from Tom Spies and recompiled them using the same minimum dbh of 25.4 cm as used for the inventory data.
Spies, Thomas A.; Franklin, Jerry F.; Thomas, Ted B. 1988. Coarse woody debris in Douglas-fir forests of western Oregon and Washington. Ecology 69:1689-1702.