Surface area of the 0- to 1-cm. fuel accounted for differences between species. 

 Presence of needles on the ponderosa pine branches provided this species with the most 

 surface area. Of the correlation between the X and Y variables, was closest to 

 Y (r = 0.57). Moisture content was nonsignificant in the regression because of the 

 small range in moisture values. X^ was nonsignificant in regressions in which species 

 were kept separate. 



Reaction Intensity 



The measured Ir values were mostly less than the predicted ones, as shown in the 

 following tabulation: 



Ponderosa pine Douglas-fir Species combined 



Average reaction intensity 



Measured, B. t.u./ft . ^-min . 4,621 3,599 4,130 



Predicted, B.t .u. /ft. ^-min. 4,800 3,808 4,324 



Average absolute deviation, percent—''' 53.6 52.8 53.2 



Overpredictions 10 9 19 



Underpr edict ions 3 4 7 



We could not substantiate conclusions about the accuracy of the model to predict Ir 

 because we were unable to measure Ij^ precisely under field conditions. There was a 

 tendency to overestimate flame depth used to calculate Ir (equation 3) because the 

 widest portion of the flame was outlined on the photographs. The fact that fuel weight 

 loss during passage of the flame front was based on an average value for all plots also 

 contributed to the deviations. 



Weight Loss Related to Particle Size 



The average percent weight loss during passage of the flame front for sample fuel 

 particles from all plots is tabulated below: 



Ponderosa pine Douglas- fir 

 Percent Percent 



Needles -'^96 



Branches by, 

 diameter^ (cm. ) 



0.2 — - 94 ± 2 



0.5 -- 80 ± 16 



1 73 ± 13 71 ± 18 



1-3 42 ±21 36 ± 15 



3-5 15 ± 7 11 ± 6 



■••Measured Ir - predicted Ir x 100 was calculated for each plot and averaged with 

 Measured Ir 



sign ignored. 



^The needles were completely consumed; however, needles contain 4 percent ash which 

 theoretically is not a weight loss. 



^Diameters were chosen to provide sensitivity at the small sizes. Inasmuch as 

 ponderosa pine and Douglas-fir branches have a different size distribution, different 

 diameters for the small sizes were chosen. 



'*The second values are standard deviations. For ponderosa pine particles, n = 26; 

 for Douglas-fir particles, n = 18. 



18 



