Figure 5. — Duff reduction 

 related to the water content 

 of the louer half of the 

 duff layer (from Shearer 

 1975). 



50 100 150 200 



DUFF MOISTURE CONTENT 

 (PERCENT OVENDRY WEIGHT) 



At 50 percent water content, the duff layer is mostly burned off, but as the water 

 content increases, a decreasing percentage of the duff layer is consumed. Above 110 

 percent, however, duff reduction drops to a uniformly low amount. 



When the results of this study are superimposed on Shearer's curve, it is not 

 surprising that lower duff water content had no significant correlation to duff consump- 

 tion. In the clearcuts, lower duff water averaged 155 percent, with a range from 71 to 

 275 percent. The shelterwood averaged 148 percent with a range from 77 to 205 percent. 

 The range of the subblock mean lower duff water contents (140 to 188 percent) is plotted 

 on figure 5 in order to clearly show that the conditions as sampled were outside of the 

 predictive portion of the curve. 



The unusually high duff moisture resulted from the high precipitation and low 

 temperature on the Coram Experimental Forest during August 1975, the month preceding 

 the fires. During that month there was a total of 4.07 inches (10.34 cm) of precipita- 

 tion, twice the normal mean, and the average daily maximum temperature was 66.9°F 

 (19.3°C), approximately 2°F (1.2°C) below normal. This was the coldest August ever re- 

 corded at the Hungry Horse Dam, and the third wettest since records were started in 1947. 



Soil Water 



None of the prescribed fires greatly changed the amount of water within the sur- 

 face 4 inches (10.16 cm) of soil; within the upper inch (2.54 cm), the average was 

 27.1 percent before, and was 26.8 percent after fires. Of the 398 samples taken 

 within the surface inch during the week of burning, 63 percent contained 20 to 30 per- 

 cent water, while 15 percent contained less than 20 percent water and 22 percent con- 

 tained greater than 30 percent water. Nearly half of the samples within the surface 

 inch increased in water following burning, probably indicating a zone of condensation 

 similar to that described by Uggla (1973). 



The amount of water within the surface inch of soil varied significantly by cut- 

 ting method. The average amount of water was least within the shelterwood cutting, 

 intermediate within the small clearcut groups, and greatest within the clearcuts. In 

 addition, the average amount of water increased (but not significantly) with greater 

 elevation by type of cutting. 



10 



