Predicting Duff and Woody Fuel Consumption in Northern Idaho Prescribed Fires

Experimental burns were conducted on 36 plots in mixed conifer logging slash in northern Idaho to investigate consumption of duff and woody fuel. Fires were conducted in spring and fall, in YUM (yarded unmerchantable material) and non-YUM dearcuts and seed-tree cuts. Preburn duff depth averaged 3.8 cm and consisted of a shallow layer of decomposing litter, averaging 2 cm, interspersed with deep pockets of rotten wood averaging 13 cm. Preburn total woody fuel quantities ranged from 63 to 193 t/ha. Regression relationships between fuel consumption and fuel characteristics were developed. Duff depth reduction was related to preburn duff depth and to a lesser extent, duff moisture content. Percent duff consumption and mineral soil exposure were related negatively to duff moisture and positively to large fuel (diameter \u3e 7.6 cm) diameter reduction. Diameter reduction of large fuel pieces was positively related to preburn diameter and negatively related to measured moisture content. Consumption of rotten material was greater than that of sound material. These relationships were compared to other empirical fuel consumption models and a theoretical model in predicting our fuel consumption. The relationships presented here can be used to predict duff and woody fuel consumption from prescribed burning in logging slash in the mixed conifer type of the northern Rocky Mountains