Figure 4. — Relationships 

 between fuel bed bulk 

 depth (first year) and 

 expected number of 

 intercepts per foot of 

 transect for modeling 

 fire behavior in slash. 



o 

 o 



O- 

 Q 



v: 



ZD 

 CO 



Q 



LxJ 

 CO 



CURVES ARE OF THE FORM Y 

 CURVE _a_ CONDITION 

 0.767 



iVx 



2 - 



1 - 



A 



B 0. 940 



C 1.22 



D 0. 542 



E 0.877 



HIGH LEAD HARVEST, ALL SPECIES 

 PRECOMMERCIAL THINNING. PINES 

 PRECOMMERCI AL THINNING, OTHERS 



GROUND LEAD HARVEST, OTHERS 

 GROUND LEAD HARVEST , P INES 



1 2 3 4 5 6 7 8 9 10 

 NO. i-to 1-INCH PARTICLE INTERCEPTS PER FOOT 



Bulk Depth Versus High Intercept Depth 



Measurement of bulk depth is time consuming and subject to personal interpretation. 

 However, the simpler to measure "high intercept depth" (Brown 1974) tends to under- 

 estimate fuel bed compactness, resulting in a systematic overestimation of the rate of 

 fire spread and reaction intensity by Rothermel's (1972) model (Brown 1972; Bevins 1976; 

 Hough and Albini 1978). But because it is rapid, reliable, and widely used, we deter- 

 mined the regression relationship between high intercept depth and bulk depth to provide 

 a formula that can be used to reduce the high intercept measurements for use in the 

 Rothermel fire spread model. The analysis was made on pairs of bulk depth and high 

 intercept depth measurements taken at each point. 



Examination of a large number of regressions for various combinations of skidding, 

 species, and age revealed no substantive differences between the regression coefficients. 



1 1 



