0.2 r 



0.15 



O 

 S 



lu 



0.1 



0.05 



280 



290 



300 



310 



TEMPERATURE, K 



Figure 5 — Decreases in recent ponderosa pine 

 needles EMC desorption values at humidities of 

 10, 30, and 70 percent as surface temperatures 

 increase are predicted and plotted from equa- 

 tions 6, 7, and 8. 



« 

 • 

 c 

 o 

 « 

 c 

 • 

 E 

 •o 

 I 



O 



< 



OA 



-L 



JL 



10 



IS 20 25 

 EMC, % 



30 



70% ftH 



30% RH 

 < 10% HH 



1 1 



320 



35 



40 



0.3 r 



0.2 



0.1 



O 



O 0.3 



O 0.2 



u. 

 o 



2 0.1 



278 °K 



NFDRS 



J I I I I I 1 I I 



300 °K 



OA 



/ .DF,CG,PP 



^:^^y' NFDRS 



J I I I I I I I I I 



0.2 r 322 °K 



0.1 



NFDRS 

 DF,QA,PP 



CG 



J L 



J I I 1 I I ) 



10 20 30 40 50 60 70 80 90 100 

 RELATIVE HUMIDITY, % 



Figure 7 — Desorption EMC's of weathered Douglas-fir, 

 ponderosa pine, quaking aspen, and cheatgrass litter 

 compared to wood used in NFDRS estimates. Data 

 from weathered material shows more similarity than 

 data from recently cast material. 



Figure 6 — Variations in Gibbs free energy relation- 

 ship for several litter fuels and conditions: Douglas- 

 fir at 300 °K, recently cast in adsorption; ponderosa 

 pine at 300 °K, recently cast in desorption; quaking 

 aspen at 278 °K, weathered in adsorption; cheat- 

 grass at 322 °K, weathered in desorption. 



Figure 7 illustrates the curves generated from 

 equation 8 and the separation for the litter groups at 

 278, 300, 322 °K, desorption, and weathered conditions. 

 A general grouping of foliar litter species was seen in the 

 firs and spruce needle EMC data. Pine needle EMC's for 

 recently cast or weathered conditions tended to group. 



Coefficients for the Gibbs free energy equation, A and 

 B, were found to be functions of temperature (figs. 4, 7). 

 Data were analyzed at 278, 300, and 322 °K for ponderosa 



pine needles, quaking aspen leaves, and Douglas-fir 

 needles. For cheatgrass, EMC data taken at 295 °K were 

 used because those at 300 °K were not available. It was 

 found that both A and B could be estimated by quadratic 

 equations where the litter temperature was the independ- 

 ent variable. For cheatgrass, a linear regression provided 

 a better fit for the A coefficient for all conditions except 

 the recently cast material in desorption. This was also 

 true for the Douglas-fir weathered material in adsorption. 

 Each of the litter groups delineated above can be evalu- 

 ated for expected EMC's by using equation 7 with Cj, C^, 

 and Cg values given in table 3 to determine A and C^, C^, 

 and Cg values to determine B and then using equations 

 6 and 8 to calculate the expected EMC. The coefficients 

 Cj and C^, and Cg, and C'j and Cg are given in table 3 



7 



