640 JOURNAL OF FORESTRY 



the percentage for lieavy burns in yellow pine. In white fir relatively 

 few trees show signs of fire,' and of these only 32 per cent or about 

 one-third are badly scarred. 



Among the factors having an influence in the initial wounding by 

 fire may be resin content, structure and relative thickness of the bark. 

 The bark of incense cedar is resinous, and is fibrous in structure. That 

 of yellow pine is resinous and, though flaky on the outside, is more 

 solid than that of incense cedar. Both white fir and Douglas fir have 

 compact corky barks which are relatively poor in resin content. 



Considering heavy burns alone incense cedar still heads the list. 

 Then follow yellow pine and Douglas fir, and lastly white fir. It is a 

 common belief that the resin content of the wood favors the formation 

 of large burns. Yellow pine and Douglas fir have resinous wood. In 

 both incense cedar and white fir, standing at the head and the end of 

 the list, the bark only contains resin while the wood is non-resinous. 

 The scattered resin cells in incense cedar wood are too insignificant to 

 influence the burning properties of the wood as compared with the 

 richer resin content of yellow pine and Douglas fir wood. 



That these open burns play an exceedingly important role as starting 

 points for serious decay in coniferous trees is well known. Meinecke's ^ 

 data on decay in relation to wounds in white fir show that in over 

 40 per cent of the cull cases the decay is traced exclusively to fire scars 

 while Boyce,-' working on incense cedar, finds that S-t per cent of the 

 severe cull cases develop from decay entering through fire scars. The 

 prevalence of decay in white fir and incense cedar which largely con- 

 tributes to the decided prejudice of the lumberman against these species 

 is thus in a large measure chargeable to fire. 



According to the data given and contrary to the general impression 

 the resin content of the wood itself does not play a leading role in the 

 burning of more severe fire scars. Resin in the bark undoubtedly adds 

 materially to the inflammability of the outer parts of the tree and 

 thereby becomes an important factor in the killing of the cambium by 

 fire. When the flames, after destruction of the bark, begin to eat into 

 the wood other factors than mere resin content govern the combusti- 

 bility of the latter and contribute to the enlargement of the original 

 injury to the serious burns so common in coniferous forests of the 

 West. 



^ Meinecke, E. P. : Forest Pathology in Forest Regulation. Bull. No. 275, 

 U. S. D. A. 1916. Pp. 51-52. 



"Boyce, J. S. : The Dry-rot of Incense Cedar. Bull. No. 871, U. S. D. A. 

 1920. P. 45. 



