and must be carried out to 3, 5, and 7 decimal places, 

 respectively, for the A and B coefficients to be accurate. 

 Rounding up EMC values imposes a bias so the values 

 are always offset from the observations. 



The EMC values over a range of litter temperatures can 

 be estimated from the equations given in tables 2 and 3 

 developed for the four litter types tested. It appears that 

 these results can be extended to the litter groups by using 

 the equations for the representative litter type because 

 the litter samples could be grouped within ±2 percent 

 of each other. Litter group 1 (recently cast, adsorption 

 and desorption) is represented by the cheatgrass EMC's. 

 Litter group 2 (recently cast, adsorption and desorption) 

 is represented by the Douglas-fir EMC's, while litter 

 group 3 is represented by the ponderosa pine EMC's and 

 litter group 4 by the quaking aspen EMC's. The weath- 

 ered samples, with adsorption and desorption phases, 

 group in a similar manner but most of the conifers needle 

 types group with the Douglas-fir and ponderosa pine 

 needle data. Groups 2 and 3 could be grouped as one 

 because the calculated EMC's are generally within ±2 

 percent of each other. 



DISCUSSION 



The possibility of organizing the various foliar litters 

 into litter groups is encouraging because it suggests that 

 only a few such groups of litters or fuels are needed to 

 describe the general change in EMC. Use of this infor- 

 mation does require the user to make observations of the 

 field situation and decide what species are present and 

 whether the foliar litter is weathered or recently cast. 

 Although the EMC data for recently cast litters are use- 

 ful for a short period of each year, the weathered EMC 

 data will probably be useful throughout the year. Weath- 

 ering results in the EMC shifting to higher values. The 

 available literature was reviewed for data that could be 

 compared to see if the results are consistent with other 

 measurements. Information published by King and 

 Linton (1963), Blackmarr (1971), and Van Wagner (1972) 

 was used to determine if the EMC's of other fuels could be 

 estimated using regression equations determined in this 

 work. Results were compared to those reported by Nelson 

 (1984) and good agreement was found. In addition, the 

 EMC equations to calculate wood moisture in the NFDRS 

 were checked. 



Litter group 1, cheatgrass (recently cast, adsorption 

 and desorption), matched Blackmarr's EMC's for wire- 

 grass (Aristida stricta Michx.) and broomsedge (Bromus 

 secalinus L.), staying within 2 percent at all the tested 

 RH's. Van Wagner's (1972) EMC data for a grass (Cal- 

 amagrostis sp.) was consistently 2 percent higher. The 

 tussock grass {Poa caespitosa) EMC's reported by King 

 and Linton were lower than that for cheatgrass by more 

 than 2 percent and had a different rate of change to RH. 

 The desorption EMC's curve for cheatgrass were 1.5 to 

 2.0 percent higher than the EMC curve presented for 

 wood. 



Litter group 2, fir and spruce needles (recently cast, 

 or weathered, adsorption and desorption), appeared to 

 be unique in that no other needles for these or similar 

 species have been tested. This group's EMC values were 



found to fit best the eucalypts (E. obliqu L'Herit. and E. 

 radiata Sieb. ex DC.) leaf data of King and Linton (1963). 

 The EMC's of the eucalpyts stayed within 2 percent of 

 litter group 2 EMC's to an RH of 70 percent, where the 

 eucalyptus litter exhibited higher EMC's. These litters 

 may group because of the extractives, crude fats, or cutin 

 they contain. At 300 °K the litter group 2 EMC's for re- 

 cently cast, desorption conditions matched the EMC's for 

 wood. 



Litter group 3, pines and cedar (recently cast, adsorp- 

 tion and desorption), EMC's behaved similiarly at low 

 RH's with red pine {P. resinosa Ait.) from Van Wagner 

 (1972) and radiata pine (P. radiata) from King and Linton 

 (1963). At 82 percent RH, however, radiata pine had a 

 9 percent higher EMC during adsorption. Although none 

 of the litter samples used for comparisons were identified 

 as weathered, five pine species were found to match best 

 with litter group 3 (weathered, adsorption and desorp- 

 tion): eastern white pine, (P. strobus L.) and jack pine 

 (P. banksiana Lamb.) from Van Wagner (1972); loblolly 

 pine (P. taeda L.), slash pine (P. elliottii Engelm.), and 

 longleaf pine (P. palustris Mill.) from Blackmarr (1971). 

 For this litter group, the match in EMC was always 

 within 2 percent until the RH increased to 80 percent 

 or more. Most of the weathered litter samples corre- 

 sponding to the litter samples of the recently cast litter 

 groups 2 and 3 merge into the weathered phase of litter 

 group 2. 



Litter group 4, quaking aspen, western larch, and west- 

 em white pine (recently cast, adsorption and desorption), 

 compared well with sugar maple {Acer saccharum Marsh.) 

 and trembling aspen (Populus tremuloides Michx.) from 

 Van Wagner (1972) up to a RH of 78 percent, where the 

 latter went to higher EMC's. (Generally, the EMC's were 

 within 1 percent at RH's below 78 percent. The deciduous 

 leaves used by Blackmarr, southern red oak (Quercus 

 falcata Michx.), post oak (Q. stellata Wangenh.), and 

 mockemut hickory {Carya tomentosa Nutt.), compared 

 best with the litter group 4 (weathered, adsorption and 

 desorption) EMC's. The adsorption values at midrange 

 RH for the oaks were about 2 percent lower in EMC than 

 those found in this study. 



The use of EMC's for the litter groups discussed here, 

 rather than those for wood, to represent foliar litter would 

 produce some significant changes in estimating fire dan- 

 ger or fire behavior. For instance, all of the litter groups' 

 EMC's are within 1 percent of each other at 278 "K (40 °F) 

 and 10 percent RH, but are 3.5 to 4.5 percent higher than 

 those for wood. At 300 °K (80 °F) and RH's from 10 to 90 

 percent, pine needles are about 2 percent higher in EMC 

 than wood and fir needles. Deciduous leaves are about 

 3.5 percent higher than wood over the same RH range. 

 This means that for a system based on the EMC of wood, 

 the fire danger or fire behavior in needle and leaf fuels 

 can be overestimated. But the reverse can happen at 

 higher temperatures, such as the 322-''K (120-''F) test 

 temperature, where all of the EMC's for foliar litters 

 become less than that for wood above 40 percent RH, 

 with cheatgrass being lower by nearly 7 percent. In these 

 cases, the litter may be ignitable sooner than expected or 

 continue to burn even though the RH shows an increase. 



9 



