Table 2. --Mean duff reduction and mineral soil exposure resulting from burning 





Q a rnT^ 1 p 

 • dill X t 



Mi n PT?i 1 1 1 









: No. : 





; Duff reduction '. 



Duff reduction 













Shelterwood ^(21-1) 



40 



7 



0.2 



5 



QVipi f p-pwoof^ ^('21-2") 



34 



13 



. 5 



18 



Small Clearcuts (12) 



20 



(2) 



1 . 1 



48 



Small Clearcuts (22) 



20 



(2) 



.8 



28 



Clearcut (15) 



91 



18 



.6 



27 



Clearcut (23) 



90 



20 



.7 



26 



^Shelterwood subblock 



mean values 



were not similar enough statistically to allow 



the subblocks to be combined. 



^No data--mineral soil exposure was not estimated. 



The fires did not spread well because of frequent fuel discontinuity, especially 

 in subblock 1, which had lighter fuel. Subblock 2 of each block burned more completely 

 and evenly as a result of heavier fuel loading. However, usually only the fine fuels 

 and litter were consumed. Within each block a number of plots did not burn, and these 

 were lost for analysis (9 and 10 out of 100 in each of the two clearcuts, and 26 of 

 100 in the shelterwood). 



Buff Reduction and Mineral Soil Exposure 



Table 2 summarizes the mean duff depth reduction and mineral soil exposure on each 

 subblock. The percentage of mineral soil exposed ranged from a high of 20 percent on 

 clearcut block 23 to a low of 7 percent on shelterwood subblock 21-1, falling short of 

 the 30 percent minimum prescribed. Mean duff depth reduction was less than 0.8 inch 

 (2.03 cm) in all blocks, amounting to a reduction of approximately 25 percent. The 

 prescription called for a 2-inch (5.08-cm) reduction to provide for an overall mean 

 duff depth reduction of about 50 percent. Again prescription goals were not met. 



These results are primarily attributed to the high water content of the duff layer, 

 especially in the lower half. Upper duff water content was above prescription limits 

 in both the clearcuts and the shelterwood, and except for block 12, lower duff water 

 content exceeded 100 percent in all blocks. 



The Rex--Fortran-4 computer program (Grosenbaugh 1967) was used for both combina- 

 torial screening and conventional multivariate regression analysis. Both mineral soil 

 exposure and duff reduction were tested against all possible combinations of independent 

 variables, up to and including sets of four. In all cases, values were so low that 

 no relationships were indicated. Various transformations and combinations of variables 

 were also tried with no significant improvements. Therefore, no regression equations 

 are presented. 



Duff Water 



The water content of the duff, especially of the lower half, has been repeatedly 

 shown to be a major influence in the reduction of the duff layer by fire (Norum 1975, 

 1977; Shearer 1975; Van Wagner 1972). However, the results of this study show no 

 relationship between them, because of the magnitude of the water contents. Shearer 

 (1975) , working in the same forest type, found that duff reduction in percent is re- 

 lated to lower duff water, only when the latter is between 50 and 110 percent (fig. 5). 



9 



