10 20 30 40 50 60 70 80 90 



RELATIVE HUMIDITY (PERCENT) 



Figure 6. — Effect of temperatupe on adsorption EMC of ponderosa pine needles 



at 75° and 90° F. 



Work by Spalt (1957) on basswood at 72° and 90° F (22° and 32° C) showed the same 

 trend to convergence at each extreme (Byram) . ^ The influence of temperature on EMC aver- 

 aged 0.056 percent EMC per degree Fahrenheit. In addition, Gisbome (1928) reported on 

 work by M. E. Dunlap for six fuel types that provided similar responses to temperature. 

 A composite response for EMC change over the temperature range of 50° to 100° F (10° to 

 38° C) provided a temperature factor of 0.050 percent EMC per degree Fahrenheit. This is 

 about half of what Van Wagner (1972) found for conifer litter, 0.113 percent EMC per 

 degree Fahrenheit. The variation observed by Van Wagner suggests that additional study 

 is needed to identify the magnitude of the temperature influence. In addition, he noted 

 a difference between species in the EMC's established for given temperatures and humid- 

 ities. For the ponderosa pine litter we tested, the EMC values for adsorption or desorp- 

 tion can be estimated by: 



Adsorption EMC = 0.891 H + 17.54 EXP [ (H - 100)/8.91] + 0.056(75 - T) (2A) 



Desorption EMC = 1.651 H + 19.35 EXP[(H - 100)/10.88] + 0.056(75 - T) (2B) 



where 



H = relative humidity, percent 

 T = fuel surface temperature, °F. 



Our EMC values were compared with EMC values for other fine forest fuels (King 

 and Linton 1963; Stamm 1964; Rothermel and Anderson 1966; Anderson 1969; Blackmarr 1971; 

 Van Wagner 1972). Monterey pine displayed EMC's about 2 percent lower than ponderosa 



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