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20 



JULY DAY 



F/gure 10— Maximum (A) and minimum (B) daily 

 temperatures of burned, litter, and mineral soil 

 surfaces at Lubrecht in July 1980. Burned sur- 

 face was measured in the clearcut (cc) and 

 mineral in the shelterwood (sw). Maximum litter 

 temperatures were the same in clearcut and 

 shelterwood. Horizontal line for maximum 

 temperatures (A) is at 133 °F—a seedling ' 

 survival threshold. 



Table 6— Hot events (percentage of possible days) by surface 



condition at the Lubrecht site. Data are for the months 

 of May through October. 



Years after logging 



Residue treatment 



Burned surface (clearcut) 

 Litter surface (clearcut) 

 Litter surface (shelterwood) 

 Mineral soil (shelterwood) 



Percentage of possible days 



— '37 



27 19 17 



14 16 25 







'First year after burning. 

 ^Second year after burning. 



than on the mineral soil surface. These differences were 

 significant for only 33 percent of the months. No CE's 

 were observed on the mineral soil or litter surfaces in the 

 shelterwood treatment, mostly because of the overstory 

 canopy. Because the mineral soil surface measured was in 

 the shelterwood treatment, it could not be directly com- 

 pared to the burned surface in the clearcut; minimums 

 were much warmer in the shelterwood than on the 

 clearcut. 



These results indicate a definite contrast between tem- 

 peratures on organic (burned and litter) surfaces and 

 mineral soil. Because the maximum and minimum temper- 

 atures of litter and burned surfaces are similar, the prob- 

 ability of temperature-related seedling mortality may be 

 similar. Lower maximum and higher minimum tempera- 

 tures on the mineral surface suggest that temperature- 

 related seedling mortality would be lower than on the 

 litter surfaces. 



Coram— Only litter and burned surfaces in the clearcut 



are compared here. From the first through the fourth 

 years after burning, average maximum temperatures on 

 the litter surface were significantly warmer than on the 

 burned surface for 79 percent of the months (May through 

 October). During the fifth and sixth years after burning 

 there were no differences between treatments. Data from 

 another clearcut at Coram, for a shorter period, showed 

 the same results. 



Hot events were observed mostly in the first year on the 

 burned surface, and then only on 5 percent of the possible 

 days. The litter surface had 24 to 42 percent of the days 

 with he's from the first through fourth years. After the 

 fourth year HE's were rare— 4 percent or less on the litter 

 surface and only 1 percent on the burned surface. 



Minimum temperatures on the burned and litter surfaces 

 at Coram varied from being equal to being 10 °F colder 

 on the litter during the first 4 years after burning. Mean 

 monthly minimum litter surface temperatures were signif- 

 icantly colder for 86 percent of the months by 2.7 to 

 5.4 °F. Cold events were not observed on either surface 

 for any year. 



Union Pass— Burned, litter, and chip surface conditions 

 are compared on the clearcut. Average maximum temper- 

 atures were not significantly different between the burned 

 and litter surfaces 6 years after treatment. Hot events 

 were observed on 62 percent of the days for both treat- 

 ments in July. Maximum temperatures measured on the 

 chip surface were significantly cooler— 13 °F— than on the 

 litter or burned surfaces (fig. 11). The HE's were observed 

 10 percent of the July days on the chip surface. 



Average minimum temperature for July was significant- 

 ly colder on the litter surface than on the burned surface 

 and colder on the chip surface than on either the litter or 

 burned surfaces (fig. 11). Cold events in July were ob- 

 served on the litter surface 10 percent of the nights, on 

 the chip surface 43 percent, and not at all on the burned 

 surface. These differences in minimum temperatures and 

 CE's are due more to slope position, which demonstrates 

 the effect of cold air drainage (fig. 12). 



12 



