CONCLUSIOIMS 



The equilibrium moisture content response curve of freshly cast ponderosa pine 

 needles is lowest of the conifer needle data examined, except for Monterey pine. 

 Differences between adsorption and desorption are slight (<1.5 percent) to 60 percent 

 relative humidity, and the spread increases with increasing relative humidity. The 

 EMC response can be described mathematically if temperature and humidity are known. 

 Woody materials, such as twigs and splints of wood, maintain lower EMC's, while grasses 

 and other herbaceous materials have higher EMC's, as much as 3 to 4 percent. 



Temperature effects on EMC seem to vary by species and range from 0.050 to 0.113 

 percent moisture content per degrees Fahrenheit . Other changes in the litter material, such 

 as crude fats, density, or possibly shape caused by weathering and aging, result in shifts 

 in EMC values. Sufficient data are not available to fully assess these influences. How- 

 ever, they seem to influence both EMC values and timelag response. 



Ponderosa pine needles, freshly cast, were found to have shorter timelags than 

 other freshly cast conifer needles; approximately 4 hours as compared to 10 to 17 

 hours. It was noted in the literature that a year's weathering changes the timelag 

 to a much shorter value, on the order of 1 hour. Although the change is felt to be 

 associated with the leaching of the crude fat and other extractives, it is not known 

 how rapidly the change in timelag occurs or what has been removed from the needles. 



EMC and timelag values for ponderosa pine needles are sufficiently different from 

 other species as to significantly affect the flammability of an area. The influence 

 upon systems to assess fire danger should be determined so the use of fire-danger rating 

 components and indices is as accurate as possible. 



Use of the experimental data for fraction of moisture change and the time for the 

 change showed moisture diffusivity to remain nearly constant during the response to 

 the test conditions. However, just as air diffusivity is changed by pressure and 

 temperatures, so may the moisture diffusivity of the litter material be changed. For 

 litter beds with bulk densities between 0.31 Ib/ft^ (0.05 g/cc) and 2.81 Ib/ft^ 

 (0.045 g/cc) the diffusivity was found to be 1.2 x 10 ^ cm^/s and for newly cast 

 needles, 2.0 x 10~^ cm^/s. 



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