Fuel-Load Reductions Resulting from Prescribed Burning in Grazed and Ungrazed Douglas-fir Stands

Abstract

Prescribed understory burning was carried out in both grazed and ungrazed Douglas-fir stands on the University of Idaho Experimental Forest. Burning conditions were moderately cool with 10-hr time-lag fuel moisture varying from 11 to 19%. Preburn and postburn fuel loadings were determined by use of the planar intersect method. Preburn data indicated greater fuel accumulations in grazed stands, 55,460 kg/ha, as compared to ungrazed stands, 44,710 kg/ha. Difficulty in achieving a satisfactory rate-of-spread and fire intensity was encountered due to the combined effects of a very dry summer followed by a wet fall. Moist conditions on the study site, lack of fine fuels, and accumulation of heavy fuels in the grazed portion produced a burn of patchy nature. Fire rate of spread varied from 0 to 183 cm/minute with flame height up to 91 cm. Result was a fuel reduction of 60.2% in the grazed stand and 35.2% in the ungrazed stand. Prolonged grazing in this area had created a dense, overstocked stand with insufficient fine fuels to carry a fire, which severely limited the effectiveness of prescribed burning.