Air Temperature 



Air temperatures at 4.5 ft above the surface in clearcut 

 units were not significantly warmer than above the sur- 

 face in uncut units at any of the sites. Comparison using 

 accumulative degree days over the May through October 

 season did not reveal significant differences either. Data 

 from Coram and Union Pass show that topographic posi- 

 tion influences air temperature much more than clearcut- 

 ting. Monthly average minimum temperatures in openings 

 at the toe of a slope were 5 to 12 °F cooler than openings 

 a few hundred feet up the slope (fig. 7). Monthly average 

 maximum temperatures were at least as warm at the toe 

 of the slope as in openings on the slope. 



Soil Temperature 



Lubrecht— Daylight average and maximum temperatures 

 in the humus (O2) layer 0.4 to 1.2 inches deep at Lubrecht 

 over the 3 years were significantly warmer on the clearcut 

 than in either the shelterwood or uncut treatments (fig. 8). 

 Humus in the shelterwood was significantly warmer than 

 in the uncut. Maximum humus temperatures were as high 

 as 136 °F on the clearcut, and July average maximum was 

 about 115 °F. The HE's occurred, but were not frequent 

 (10 during the 3 years). Maximums on the shelterwood 

 were nearly as high at 131 °F, with a July average max- 

 imum of 111 °F in 1978. Temperatures were much colder 

 in 1979 and 1980, with a July average of about 86 °F. 

 Only three HE's occurred in the shelterwood, all in 1978. 

 The maximum humus temperatures on the uncut site were 

 91 °F. 



Minimum and night average humus temperatures were 

 significantly colder on the clearcut than in the shelterwood 



or uncut treatments. Minimimn humus tem.peratures ob- 

 served (May through September) were 18 °F in the clear- 

 cut and 21 °F in the shelterwood. Average July minimums 

 were 43 °F in the clearcut and 50 °F in the shelterwood 

 and uncut treatments. 



Other Sites— Humus or upper level soil temperatures at 

 Coram and Union Pass were measured at depths from 1.2 

 to 2.0 inches. Absolute maximum temperatures ranged 

 from 73 to 90 °F in the clearcut and were significantly 

 warmer than in the uncut treatments. Night minimums at 

 Coram in the clearcut were not significantly colder than in 

 the uncut. The clearcut at Union Pass was significantly 

 warmer at night than the imcut for the short measure- 

 ment period. We do not know the reason for this reversal, 

 yet the 24-hour cumulative num.ber of degree hours— those 

 greater than 32 °F— is 80 percent higher in the clearcut 

 than in the uncut. 



Soil temperatures at depths from 2 to 16 inches were 

 only measured on clearcut and uncut treatments at Union 

 Pass. Temperatures at these depths were significantly 

 warmer in the clearcut than in the uncut. Temperatures at 

 2 inches deep averaged nearly 12 °F warmer in the clear- 

 cut broadcast burn than in the uncut, 11 °F at the 8-inch 

 depth, and almost 10 °F more at the 16-inch depth (fig. 9). 



Summary 



Temperatures increased from the ground surface to 

 depths of 16 inches as a result of clearcutting. Site loca- 

 tion has little or no effect on the treatment differences, 

 though the maximums and average temperatures are 

 higher at some locations. The magnitude of differences 

 decreases with increasing depth, yet the differences re- 

 main statistically significant. 



70 



60 



50 



40 



30 



20 



MD-SLOPE 



SLOPE TOE 



M 



J A 



1975 



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M 



J J A 



1976 



T 



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 LJ 



100' 



to 

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 < 



60- 



50 



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UNCUT 



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15 20 



JULY DAY 



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25 30 



Figure 7— Mean monthly minimum air 

 temperatures at ttie toe of a slope and at 

 midslope on the Coram Experimental Forest. 

 Temperatures are for May through October of 

 1975 and 1976. 



Figure 8 — Daylight average temperatures of the 

 .humus (O2) layer (0.4 to 1.2 inches depth) on the 

 clearcut (cc), shelterwood. (sw), and uncut 

 treatments at Lubrecht in July 1980. Surface 

 condition was litter. 



10 



