Evaluation of Mechanized Thinning and Prescribed Fire Effects on Long-Term Fuels Accumulations in Uneven-Aged Jeffrey Pine

Abstract

Forest thinnings implemented through cut-to-length and whole-tree harvesting followed by underburning were evaluated for their effects on long-term downed and dead fuels accumulations in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) accompanied by isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on an initial inventory consisting of dry weight and fuel bed depth measurements conducted posttreatment, accumulations in the cut-to-length treatment were elevated according to most measures. Burned stand portions exhibited smaller quantities of fuels initially in individual timelag categories and in total as well as reduced fuel bed depths compared to their unburned counterparts except for the 1,000-hr fuels in the whole-tree treatment where postburn mortality of small stems nullified this effect. A linkage between initial mortality resulting from prescribed fire and final 1,000-hr fuels, as measured 8 yr later, was established but was probably attributable to combined thinning and burning effects. Over the course of the study, either greater accruals or diminished reductions in loading were apparent within burned stand portions compared to unburned portions, most notably in the whole-tree treatment. Results presented here provide insight into potentially compromised fuels reduction outcomes when implemented in uneven-aged stands on dry forest sites.