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.
Changes in forest structure, spatial pattern and composition from prescribed fire and thinning in Sierra mixed conifer.
Parks, Sean*,1, North, Malcolm1, Innes, Jim1, Oakley, Brian2, 1 Sierra Nevada Research Center, Davis, CA2 College of Forest Resources, Seattle, WA
ABSTRACT- After a century of fire suppression, thinning and prescribed fire are widely use in western forest restoration, yet there is little information about their ecological effects on forest structure and composition. Using 18 replicated 4 ha plots in old-growth Sierran mixed conifer, we examined changes in tree basal area, density, composition and spatial pattern following 6 treatments in a full factorial design: prescribed burn/no burn was crossed with no harvest, understory thinning (25 cm dbh < remove all trees < 76 cm dbh) and overstory or shelterwood thinning (remove all trees > 25 cm dbh, except 22 large, evenly spaced trees/ha). We measured treated stand structure against hypothesized pre-European structure developed from on-site age reconstruction and active-fire regime old-growth in Yosemite. Thinning intensity had the most significant impact on basal area and density while fire had little impact. Fire, however, significantly shifted composition toward more shade-intolerant species, and composition following the fire/shelterwood treatment had a much higher percentage of pine than pre-European forests. Current mixed-conifer spatial pattern is highly patchy and fire reduced tree clump/gap contrast more toward historic density and distribution. Thinning markedly changed spatial patterns and shelterwood spacing was a significant change from historic forest patch pattern. The burn/no thin treatment had little effect on forest conditions because fire intensity and extent was limited due to late-fall weather conditions. In our study, the understory thinning and prescribed fire treatment produced a structure and composition closest to hypothesized pre-European conditions.
Key words: stand structure, prescribed fire, forest restoration, spatial pattern