is derived by simply adding maximum windspeed in miles per hour, air temperature in 

 degrees Fahrenheit, and vegetation cover in percent (wind mi/h + °F + percent veg. 

 cover = score). If metric measurements are used the formula is 0.6 (km/h) + 1.8 (°C) 

 + percent veg. cover + 32 = score. 



Considering the three fire class ratings of 1, 2, and 3 (table 2), a score of less 

 than 110 will not provide conditions necessary for burning (class 3) . A score of 110 

 to 125 indicates conditions prevail for a class 2 fire. A score of 125 to 130 indicates 

 conditions are optimum for a class 1 or self-sustaining fire that will carry itself 



Figure 6. — A class 1 or self-sustaining five capable of carrying through the vegetation. 



May 9 3 1975, bum at White River , Nevada. 



(fig. 6) . A score higher than 13'0 indicates a hazardous condition in the scattered and 

 dense pinyon- juniper communities when burning should not be attempted. 



When these simple scores were compared on 17 bums (table 2), 15 of the 17 (88 per- 

 cent) were correctly classified. A discriminant analysis (Klecka 1975) was used to con- 

 struct a weighted score of the variables- -wind, temperature, and cover--to separate the 

 burns into three classes. This more sophisticated method correctly classified 82 percent 

 of the burns. With more observations, these results would change; however, the simple 

 score method compares very favorably with the discriminant analysis. 



This simple scoring applies to the cooler months of April, May, October, and Novem- 

 ber, or anytime when air temperatures are below 75 °F and windspeeds are above 5 mi/h. 

 Total vegetation cover varied from 42 to 66 percent on all successful burns (table 2) . 

 Forb and grass cover was minimal in all areas. 



There appears to be a narrow separation between conditions necessary for prescribed 

 burning which will adequately carry a fire and those of a wildfire which develop concern 



9 



