The longer timelags may be partially due to the soaking before the test and the higher 

 relative hiomidities used for end points. Only Blackmarr had end conditions similar to 

 ours and although he presoaked the material, he obtained timelags comparable to ours. 



Although we are not reporting results for weathered needles because tests are 

 still being conducted, data in the literature show a dramatic shortening of the 

 timelag: 



Spec-ies Timelag Drying condition Reference 



Hours °F Fercent 



relative 

 humidity 



Ponderosa pine 



1 , 



.28 



80 





20 





Fosberg (1975) 



Lodgepole pine 



1, 



,01 



80 





20 





Fosberg (1975) 



Monterey pine 



1, 



,08 



83 





56 





King and Linton (1963) 



Red pine 



4, 



,20 



78 



±2 



35 



±5 



Van Wagner (1969) 



Red pine 



7. 



.00 



78 



±2 



55 



±5 



Simard (1968b) 



Eastern white 

















pine 



3, 



,50 



78 



±2 



55 



±5 



Simard (1968b) 



Jack pine 



4, 



.00 



78 



±2 



55 



±5 



Simard (1968b) 



White spruce 



5. 



.00 



78 



±2 



55 



±5 



Simard (1968b) 



Variations in timelag may be due to the wax and resin content, as suggested by Van 

 Wagner (1969) . This could account for the shorter and variable timelags in weathered 

 needles noted by Simard (1968b) . It appears that the timelags are significantly dif- 

 ferent by species and weathering, which may be associated with the amount of waxes, 

 oils, and varnishes on the surface and in the pores of the needles. Therefore, the 

 results we are reporting probably only apply to freshly cast litter in ponderosa pine 

 forests . 



Generally, reports on timelags of fuels experiencing desorption or adsorption 

 show the timelags to be longer for adsorption (Kerr and others 1971; Simard 1968b). 

 Although the needle tests did not show this response, it did exist in the litter bed 

 tests . 



As the bulk density increased, the timelag increased but showed a leveling of 

 timelag at the most dense value tested (fig. 8a) . This leveling, or plateau, may be 

 due to air velocities over and through the litter bed or may represent a zone of bulk 

 densities where diffusion through the voids is limited by the moisture diffusivity of 

 the particles. This consideration is pointed out by Fosberg (1975) in his theoretical 

 development of heat and moisture flux in litter and duff. The responses obtained in 

 this study tend to support the theoretical approach Fosberg has developed, but ad- 

 ditional tests with varying bulk densities and litter depths are needed. . 



The desorption response of the litter bed with solar heating included appears to 

 be inverse to the expected. Response time was found to become shorter as bulk density 

 increased (fig. 8b) for desorption. With adsorption conditions established and solar 

 heating turned off, the response is similar to previous adsorption tests. Some 

 lengthening of timelag was observed, reflecting the thermal relaxation of stress back 

 to ambient air temperature. 



Little moisture response data are available to compare with theoretical develop- 

 ments such as Fosberg's (1975), but the litter bed tests we conducted at a bulk density 

 of 2.81 Ib/ft^ (0.045 g/cc) were compared to the profiles Fosberg (1975) presented in 

 figure 8 of his paper. Since the experimental measuring methods we used provided the 

 average moisture content of the bed, comparison to Fosberg's theoretical results re- 

 quired averaging his moisture content profile at each depth over time. Both thermal 



14 



