PRESCRIBED BURNING IN UNEVEN-AGED STAND MANAGEMENT OF PONDEROSA PINE DOUGLAS-FIR FORESTS

The purpose of this study was to examine the effects of low intensity prescribed fires on wildfire hazard reduction, site preparation and tree mortality of uneven-aged managed ponderosa pine/Douglas fir (Pinus ponderosa/Pseudotsuga menziesii) forests. The study also provided the opportunity to determine the effects of uneven-aged silviculture on fire hazards. Burning followed the individual-tree selection cutting and full-tree utilization of an uneven-aged silvicultural prescription, which was developed for two stands in western Montana, U.S.A. Prescribed burning, following the full-tree utilization, proved to have no usefulness on fire hazard reduction. Uneven-aged cutting without any fuel management treatment showed substantial fire behavior potential, far beyond the control limit of direct attack methods. Residual duff depth was not significantly different between the burned and the unburned treatment units. Mineral soil exposure of the burned unit was significantly greater than the unburned unit in only one of the study stands. Removal of the litter fuels was significantly greater in the burned units, contributing to a receptive seedbed for natural regeneration of shade-intolerant tree species. Fire succeeded in eliminating Douglas fir regeneration. Losses of ponderosa pine seedlings were substantial, but a few saplings and seedlings did survive the fire. Fire also killed 6·5 to 9% of the overstory trees (over 3 m in height). Overstory mortality was statistically significant, but this mortality was confined to smaller trees (less than 12 cm in d.b.h.). Guidelines are offered for a safe and effective prescribed burning under standing timber in ponderosa pine stands. © 1992 Academic Press Limited.