Duff reduction by prescribed underburning in Douglas-fir.

Predictive equations for duff reduction and mineral soil exposure by prescribed fire are presented. An explanation is suggested for the dependence of duff combustion on surface fuel combustion. Surface fire duration and fuel moisture estimates of the National Fire-Danger Rating 1,000-hour timelag are the best predictors for reduction in moist duff. Duff layers with less than 30-percent moisture burned independently of surface fires.