PARENT SESSION
OOS 5: Restoration Effects of Fire and Thinning Treatments on Mixed-Conifer Ecosystems.
Organized by: M North and J Innes
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 148.
Effect of silvicultural treatments and perscribed fire on coarse woody debris dynamics in a sierran old-growth mixed-conifer forest.
Innes, James*,, North, Malcolm,
ABSTRACT- Although coarse woody debris (CWD) serves several important ecosystem functions including providing wildlife habitat, nutrient and moisture reservoirs and long-duration fire fuel, the effect of widely applied restoration treatments such as fire and thinning on CWD are poorly understood. Using plots that received a combination of fire and thinning treatments, we mapped all logs greater than 30 cm (small-end diameter) in 72 ha of an old-growth mixed-conifer forest in the Sierra Nevada, California before and after treatments. We hypothesized that: 1) cutting alone would increase the density, volume and mass of CWD; 2) mean piece large-end-diameter and volume would decrease with thinning since most remaining CWD would be slash; 3). Plots that were burned or burned and cut would see a decrease in density, volume and mass. Coarse woody debris in the cut only plot increased from 46 to 75 pieces per ha and mean piece volume and diameter decreased significantly (p< 0.05) from 4.8 to 2.6 m3 and 77 to 61 cm, respectively. Plot-level volume (m3)and mass (Mt), however, decreased by 10 and 4 % respectively. In the burned, and cut and burned plots decreases in volume and mass ranged from 70 to 40% and 69 to 20% respectively. In all burned and cut plots average piece size and diameter decreased significantly. In the burn only treatment, diameter decreased by only 8 cm, compared to the burn and cut treatments with a 20+ cm decrease. These data suggest that thinning and fire alters the structure of CWD more so than fire alone. In addition, fire effects on CWD appear to be highly variable in space and time due to factors such as season of burn, fire intensity and topography, and that the legacy pattern of unconsumed CWD that is created can be long lasting.
Key words: forest structure