Figure 7. — Average adsorption and 

 desorption curves of reindeer 

 lichen at 80° F. ; adsorption 

 condition was a relative 

 humidity step change from 

 20 to 90 percent; desorption 

 condition was a relative 

 humidity step change from 

 90 to 20 percent. The 

 fraction of total evaporable 

 moisture in the sample, E, 

 was plotted against time. 



o Adsorption 

 O Desorption 



.001 



100 



200 



300 400 



t(min.) 



500 600 



The equilibrium moisture content data indicated a slight hysteresis loop between 

 adsorbing and desorbing conditions. Reindeer lichen data (averages of the adsorption 

 and desorption moisture content values) were plotted with the National Fire-Danger 

 Rating transitional and cured moisture curves and the equilibrium moisture content 

 data in the "Wood handbook." ^ All data used were based on an air temperature of 

 about 80°F. The National Fire-Danger Rating transitional moisture curve comes closest 

 to approximating the equilibrium moisture content of reindeer lichen determined by 

 this study (fig. 8). 



Field inspection in Alaska showed that lichens become dry and brittle following 

 exposure to direct sunlight. Insolation heats fuel surfaces and is important to 

 determinations of moisture content in living reindeer lichen. Future tests will in- 

 clude insolation as an influencing factor on equilibrium moisture content and timelag. 



^U.S. Dep. Agr., Forest Serv. Wood handbook. Agr. Handb. 72, 528 p., Forest Prod. 

 Lab., Madison, Wis. 1955. 



7 



