Table 1. — The heat content of various species 



Species 



Anatomical 

 portion 



High heat 

 value 



Source 







B.t.u./lb. 





Basswood {Tilia americana) 



xylem 



8,341 



Fons et al. (1960) 



Bitterbmsh {Purshia tridentata) 

 Spring 

 Summer 

 Fall 



leaves 



8,703 

 7,933 

 8,647 



Short et al. (1966) 



Longleaf pine {Pinus palustris) 



xylem 



8,771 



Fons et al. (1960) 



Magnolia {Magnolia grandiflora) 



xylem 



8,561 



Fons et al. (1960) 



Manzanita {Arctostaphylos uiscida) 



leaves 

 twigs 



9,208 

 8,676 



Countryman (1964) 



Manzanita {Arctostaphylos pungens) 



leaves 



9,070 



Davis (1968) 



Maple {Acer saccharum) 



xylem 



8,543 



Fons et al. (1960) 



Mountain mahogany {Cercocarpus montanos) 

 Spring 

 Summer 

 Fall 



leaves 



8,483 

 8,309 

 8,395 



Short etal. (1965) 



Pinyon pine {Pinus monophylla) 



leaves 

 stems 



9,480 

 8,718 



Countryman (1964) 



Ponderosa pine {Pinus ponderosa) 



needles 



9,449 



Mutch (1964) 



Sagebrush {Artemisia tridentata) 

 Spring 

 Summer 

 Fall 



leaves 



8,527 

 8,777 

 9,094 



Short et al. (1965) 



Sphagnum moss {Sphagnum spp.) 





7,918 , 



Mutch (1964) 



White fir {Abies concolor) 



xylem 



8,660 



Fons et al. (1960) 



The heat contents of most w^ildland fuels 

 are quite similar, as shown in table 1. This 

 fact has led many to conclude that chemical 

 composition and heat content changes of 

 fuels are relatively unimportant, compared to 

 their physical properties. However, some 

 studies have been made; Richards (1940) 

 found an increase of 1,300 B.t.u./lb. for 

 snowbrush {Ceanothus velutinus Dougl.) dur- 

 ing the fire season (fig. 1). A corresponding 

 increase in extractives from 5.2 percent in 

 June to 11.5 percent in September was also 

 noted. Richards concluded that the heat con- 



tent change would have a minor effect on 

 burning rate as compared with moisture 

 changes. Several range ecology studies have 

 also found corresponding seasonal trends in 

 extractives- and heat content (Short, Dietz, 

 and Remmenga 1966; Dietz, Udall, and 

 Yeager 1962) (fig. 2). I'he relationship be- 

 tween heat content and extractives is sup- 

 ported by evidence that plant parts with high 

 extractive content, such as pine needles or 

 chaparral leaves, have higher heat contents 

 than stems and xylem. 



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