over periods 2 and 3, then declines for remaining periods. We have observed this 

 trend in tests of other fuels also. Because diffusivity is moisture dependent, the 

 quadratic term in the diffusion equation prevents a simple mean value approximation 

 from being made.^ Adsorption and desorption curves for reindeer lichen show fuel 

 responses to humidity step changes at 80°F. (figs. 4 and 5). The equilibrium moisture 

 content results are shown in table 2 and plotted in figure 6. 



5 10 15 20 25 30 35 40 45 



Timednin. xlO ) 



Figure 4. — Adsorption curve of reindeer lichen for a humidity step change 

 of 20 to 90 percent at 80° F. Symbols represent replicates . 



» ^ ft 



I I I I I I I I I I 



5 10 15 20 25 30 35 40 45 



Time (min. x 10) 



Figure 5. — Desorption curve of reindeer lichen for a humidity step change 

 of 90 to 20 percent at 80°F. Symbols represent replicates. 



^M. A. Fosberg , R. W. Mutch, and H. E. Anderson. Laboratory and theoretical com- 

 parison of desorption in ponderosa pine dowels. USDA Forest Serv., Rocky Mountain 

 Forest and Range Exp. Sta., Fort Collins, Colo. (In preparation.) 



4 



