Fuel Bed Alterations by Thinning, Chipping, and Prescription Fire in a Sierra Nevada Mixed Conifer Stand

Abstract

Thinning using cut-to-length harvesting coupled with on-site slash chipping and redistribution and followed by prescribed underburning were assessed for their impacts on downed and dead fuels in an eastern Sierra Nevada mixed conifer stand. California white fir (Abies concolor var. lowiana [Gord.] Lemm.) dominated stand composition and was targeted in the thinning operation while Jeffrey pine (Pinus jeffreyi Grev. & Balf.), sugar pine (Pinus lambertiana Dougl.), incense-cedar (Libocedrus decurrens Torr.), and California red fir (Abies magnifica A. Murr.) were less prevalent. Thinning increased total fuel loading 6% and bed depth 14% but the chipping operation confined the additions to the 1+10-hr and 100-hr timelag categories. Subsequent underburning consumed the fuels produced by the mechanical treatments plus a substantial portion of the preexisting load, and the resulting reduction in total loading was almost twice that combusted in the absence of the thinning and chipping operations. Among an array of regression models used to evaluate assorted variables for their predictive capacity regarding downed and dead fuels, positive correlations between both 1+10-hr and total fuels prior to treatment and pretreatment basal area were prominent. Results reported here quantify fuel load modifications from management practices that are being increasingly utilized to enhance stand health and fire resilience in the Lake Tahoe Basin and surrounding forests.