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.
Tree regeneration strategies in response to burning and thinning restoration treatments in Sierran mixed-conifer forest.
Zald, Harold*,1, Gray, Andrew1, 1 Pacific Northwest Research Station, Corvallis, Oregon, USA
ABSTRACT- Thinning and burning treatments have been proposed to restore dry-site forest types impacted by a century of fire suppression in the western U.S. This study examined tree regeneration response to a variety of restoration treatments in a mixed-conifer forest in the Sierra Nevada of California. Treatments were imposed in a factorial design of two burn treatments (unburned, burned) and three thinning treatments (unthinned, moderate thin, and shelterwood cut), replicated thrice on 4 ha plots. Regeneration studies included pre- and post-treatment systematic surveys of understory trees (<5 cm Diameter at Breast Height (DBH)), and sowing of tree seeds in selected patch types. Shade-tolerant Abies concolor and Calocedrus decurrens dominated the pretreatment regeneration pool, followed by Pinus lambertiana and Abies magnifica, with Pinus jeffreyi, Prunus emarginata, and Quercus kelloggii being minor components. Frequency of most species was strongly associated with soil moisture abundance and light levels. Most species occupied distinct portions of the light and moisture gradients, but A. concolor, C. decurrens, and P. lambertiana all occurred in similar conditions. Reductions in density of understory trees were somewhat greater in the thin-and-burn than in the thin-only treatments, with the greatest reductions seen in the shelterwood treatments. However, natural regeneration, particularly of A. concolor and C. decurrens, was rapid and dense, particularly in the moderate-thin treatments. Regeneration of P. lambertiana was relatively uniform across treatments. Survival of germinants was greatest for the pines, with the greatest initial mortality seen in the burn-shelterwood treatments. The similarity of the dominant species environmental niches and the initial regeneration response make it unclear whether these treatments alone will lead to increased dominance of pines in these stands.
Key words: fire, regeneration, mixed-conifer, thinning