diameter growth of 30 to 50 percent can be expected in larger trees when crowns 

 are damaged more than 50 percent . 



The smaller trees, which were generally in the intermediate and suppressed 

 crown classes, showed average or even better growth following the fire. The 

 thinning effect of the fire had released these trees more than the larger 

 trees . 



The reduced diameter growth following a fire cannot be considered of major 

 importance because it is only a temporary reduction that probably will be off- 

 set by the releasing effect of the thinning. 



Height growth was similarly studied, but no correlation with fire damage 

 was found. Height growth followed closely the expected height growth read 

 from site curves. 



CONCLUSIONS AND SUMMARY 



Young ponderosa pine trees can withstand considerable fire damage without 

 serious mortality. Their resistance appears to be superior to that of older 

 trees of the same species for a given amount of crown injury. Fire is some- 

 what selective in its killing effect: it kills the smaller, weaker trees in 

 greater proportion than the larger, more vigorous components of a stand. This 

 characteristic has been cited as evidence in support of prescribed burning as 

 a tool for thinning in dense, young stands (_5 ) . 



Results of this study on 200 trees burned in 1949 can be summarized as 

 f ol lows : 



1. Virtually all mortality occurred during the first 2 years following 

 the fire. 



2. Mortality was directly related to crown injury: (a) all trees died 

 whose crowns were 90 percent or more burned, and (b) mortality was only 6 to 

 24 percent when less than 80 percent of the crown was burned. 



3. Small trees suffered greater mortality than large trees having the 

 same degree of burn. 



4. Second-year mortality was restricted to trees smaller than 6 inches 

 d.b.h. except where crown injury had been 80 percent or greater. Second-year 

 mortality probably was related more closely to bole injury than to crown 

 injury . 



5 . Crown injury of 50 percent or more appeared to have reduced diameter 

 growth in trees 6 to 9 inches d.b.h. 



6. Height growth was not affected by burning. 



7 



