CONCLUSIONS AND DISCUSSION 



The conclusions that can be made from this study are: 



1. The 1- and 2-year-old needles of ponderosa pine and Douglas-fir exhibited no 

 difference in moisture trends between 1968 and 1969. The lows for both species probably 

 occur in winter or early spring, followed by a gradual increase during the summer. 



No evidence was found of a summer drying trend that could indicate a relationship be- 

 tween lower needle moisture and susceptibility to crovm fires. The effect of new 

 needle moisture is probably insignificant in spring because of the small mass. As this 

 mass approaches 20-25 percent of the total foliage, the moisture content approaches that 

 of the older needles. 



2. The major change detected in ponderosa pine and Douglas-fir needles was in 

 their ether extractive content. Generally there was a sijmmer increase of about 100 

 percent for fir. The changes in pine were much smaller, although it remained relatively 

 high throughout the fire season. The biggest gain in fir occurred in the driest year. 



A downward trend, corresponding to the beginning of August rains, occurred in 1968. A 

 comparison between years is complicated by the change in sample site location. 



3. The energy content of the needles of these two species was highest in the late 

 summer. Although the energy of fir increased due to extractive increase, the energy 



of the extracted fuel also increased. The energy change in pine was due as much to the 

 energy change in the extractives as it was to any increase in extractives. 



These conclusions regarding crown fire potential of conifers in the northern 

 Rocky mountains lead to interesting speculations. The extractives are probably more 

 important than the seasonal changes in energy levels in terms of ignition and fire 

 propagation rates. Extractives may provide a significant aspect of flame propagation 

 within conifer crowns, and the doubling of these compounds in fir during the fire 

 season could be important to the possibility and extent of crowning. 



Another interesting possibility is that fir responds differently than pine to 

 summer drought with regard to accumulations of extractives. Perhaps the crowning 

 potential of pine is high for a greater portion of the year because extractives remain 

 uniformly high, while fir is only high in croming potential during the drier fire 

 seasons because its extractive content varies with drought. 



The seasonal energy changes of Douglas -fir and ponderosa pine foliage were only 

 about 500 B.t.u./lb.; since this is less than 10 percent of the total energy of the 

 needles, it would not seem too important. But when the availability of living needle 

 energy to the combustion process is probably far less than 8,000 to 9,000 B.t.u./lb., 

 then a gross 10-percent increase may be more meaningful. Since Hjj^££ for ponderosa 

 pine needles remained quite uniform through the season, the energy increases of fir 

 foliage are probably of more value in the predictions of cro\\Ti fires. 



The importance of seasonal changes in foliar moisture to crown fires seems to 

 need reevaluation. Actually there was little difference in moisture trends of needles 

 between the wet 1968 season and the dry 1969 season. This difference was not tested 

 due to the sampling site change. Mature Douglas -fir and ponderosa pine foliage 

 increased in moisture content during each fire season. Apparently, foliar moisture 

 content is not directly related to summer drying. Perhaps the extractives, or some 

 portion of them, need to be considered along with moisture content in approaching the 

 problem of crown fire susceptibility. Could it be that foliar extractives are 

 volatilized through a steam distillation mechanism in a fire and that an increasing 

 moisture trend enhances this combustion process within coniferous cro™s? Obviously 

 more work is needed to investigate such a possibility. 



14 



