INTRODUCTION 



Why does fire behavior show a seasonal change? Generally speaking, this occurs 

 because of changes in the fire environment. Moisture content traditionally has been 

 cited as the important change in fuel that conditions flammability and fire behavior 

 (Hawley 1926; Davis 1959). The moisture contained in fuels is important because it acts 

 as an energy sink, diluting the volatiles, and excluding oxygen from the combustion 

 zone. There are many studies on moisture content of living plants,^ but only a few 

 apply to this paper that discusses moisture, ether extractives, and energy of conifer 

 crowns . 



In the late 1930 's Connaughton and Maki^ found that moisture content of ponderosa 

 pine foliage varied inversely with soil moisture and climatic drying during the fire 

 season in northern Idaho. The fact that moisture content increases in ponderosa pine 

 foliage during June, July, and most of August is interesting since crown fires are 

 more prevalent as the fire season progresses in this region. 



Philpot found the same general situation in ponderosa pine in the central Sierra 

 Nevada of California with moisture increasing through most of the fire season and then 

 leveling off. ^ A similar trend was also found for pinyon pine and juniper in Arizona 

 and Utah (Jameson 1966), and for five coniferous species in eastern Canada (Van Wagner 

 1967). After finding high moisture contents in conifers in the Lake States during 

 periods of high crown fire potential, Johnson (1966) concluded, "In our search for a 

 satisfactory explanation for crown fires, we must apparently look beyond needle 

 moisture content." 



Can our concept of fire environment go beyond the commonly accepted fire climate- 

 fuel moisture basis of fire occurrence? Dry seasons and moisture content regimes 

 certainly determine the actual fire seasons, but recent studies suggest that inherent 

 plant chemistry and chemical changes contribute materially toward the availability of 

 energy to the combustion process (Philpot 1968, 1969a). Plant communities which have 

 survived fires for tens of thousands of years may not only have selected survival 

 mechanisms, but also inherent flammable properties that provide a competitive advantage 

 and contribute to perpetuation of fire-dependent communities (Mutch 1970) . This 

 broader concept of fire environment encompasses not only moisture relations, but inher- 

 ent energy and physical properties as well. 



Since living foliage contributes significantly to the energy field of many large 

 fires, the objective of this study was to determine simultaneous trends of moisture 

 contents, ether extractives, and heat contents for Douglas-fir (Pseudotsuga menziesii 

 L.) and ponderosa pine (Pinus ponderosa Laws.) foliage during the 1968 and 1969 fire 

 seasons. These three variables should be studied together to arrive at meaningful 

 conclusions about their relative importance to seasonal fire behavior. 



•^C. W. Philpot. Vegetation moisture trends in the central Sierra Nevada. (Unpub- 

 lished master's thesis on file at School of Forestry, Univ. of Calif., Berkeley) 

 53 p., 1963. 



^C. A. Connaughton and T. E. Maki. The volatility content (particularly moisture) 

 of evergreen foliage during periods of drought stress. (Unpublished office report USDA 

 Forest Serv. oti file at Intermountain Forest and' Range Exp. Sta., Northern Forest Fire 

 Lab., Missoula, Mont.) 1935. 



^Philpot, op. cit. 



