INTRODUCTION 



An understanding of fine fuel moisture responses is necessary for effective 

 interpretation and application of the National Fire-Danger Rating System. As improve- 

 ments are made in the National Fire-Danger Rating System, knowledge of the moisture 

 responses of common wildland fuels in the United States becomes increasingly important. 

 This report summarizes results of laboratory tests to determine adsorption-desorption 

 timelags below fiber saturation and equilibrium moisture contents of reindeer lichen, 

 [Cladonia spp.J. The fuel tested was collected in the vicinity of Fairbanks, Alaska, 

 in August 1967. Byram^ described the usefulness of timelag in comparisons of the 

 drying characteristics of forest fuels. He defined desorption timelag as the time re- 

 quired for a fuel to lose 63.3 percent of its initial moisture content above equilibrium 

 (or to lose 1 - of its moisture content above equilibrium where e is the base of 

 natural logarithms). Under adsorbing conditions, timelag is the time required for a 

 fuel to gain 63.3 percent of the initial moisture content below equilibrium. Equilib- 

 rium moisture content is the moisture level finally attained that is uniformly present 

 in fuels exposed in an atmosphere of fixed temperature and humidity; this occurs when 

 vapor pressure in the fuel equals vapor pressure in the atmosphere. 



METHODS 



Intact sections of lichen fuels were placed in an environmental chamber for the 

 duration of adsorption and desorption timelag tests (fig. 1). For adsorption tests, 

 the temperature was kept constant at 80°F. while the humidity was stepped from 20 to 

 90 percent. For desorption tests, the temperature was held at 80°F. while humidity 



Figure 1. --Reindeer lichen samples 

 suspended on nrtarosoale 

 transducers in environmental 

 chamber. The solar radiation 

 lamps in the top of the 

 compartment were not used 

 in these tests. 



^George M. Byram. An analysis of the drying process in forest 

 (Paper presented at the Int. Symp. on Humidity and Moisture, Wash., 

 1963.) 



fuel material. 

 D.C. , May 20-23, 



