70 



60- 



i '50- 



LJ 



O 



< „ 



a: 40 • 



30 



< 



A 









\ 



BURNED 

 / — UTTER 



* 





— ^. ^^■>^IPS 



> 



1 



UNCUT 



1 



70 



60- 



50- 



30- 



B 





BURNED /* 





S _ / - ^ N _ 





UTTER 



CHIPS 







* 



UNCUT 



5 10 



JULY DAY 



Figure 9— Average soil temperatures at depths of 

 2 inches (A), 8 inches (B), and 16 inches (C) for 

 burned, litter, and chip surface conditions in 

 clearcut and uncut treatment units. Data are 

 from Union Pass in July 1979. 



These results for soil temperature seem to be explained 

 well by the effects of Rn as influenced by overstory re- 

 moval. Although \/KC affects the rate of conduction and 

 associated temperature changes, this factor was over- 

 whelmed by the differences in R7i at the surface of the 

 treatments. These effects mil be discussed in more detail 

 for the surface conditions. 



SURFACE CONDITION AND 

 TEMPERATURE 



Surface conditions resulting from residue treatment in- 

 cluded litter, burned, mineral soil, and chips. The effect of 

 surface condition on surface, air, and soil temperatures is 

 examined by comparing temperatures for the different 

 surface conditions under the same overstory treatments. 

 The clearcut was used for all but one comparison. The 

 shelterwood treatment is used in that one. 



Surface Temperature 



Lubrecht— Maximum surface temperatures on both the 

 bui-ned and litter surfaces in the clearcut were greater 

 than 133 °F during midsummer (fig. 10). For the first 

 2 years after burning, average maximum (monthly) tem- 

 perature on the burned surface was 9 to 16 °F greater 

 than on the litter surface. For 57 percent of the months 

 for May through October, these differences were signifi- 

 cant. After 2 years, a hea\^^ stand of bull thistle and its 

 thistledown on the burned treatment pro\'ided enough 

 shade to decrease surface temperatures below those on the 

 litter surface. 



Hot events occurred on the burned and litter surfaces 

 from 17 to 37 percent of the days from May through Octo- 

 ber (table 6). The HE's were observed for more than 

 30 days each year after burning on both litter and burned 

 surfaces, even though instrument difficulties resulted in 

 45 days when temperatures could not be measured. 



Minimum temperatures were not significantly different 

 for the burned and the litter surfaces for most months. 

 After the thistle crop developed on the burned treatment, 

 minimum temperatures were significantly warmer on the 

 burned surface than on the litter surface. Both the litter 

 and burned surfaces had significant numbers of CE's in 

 1979— the first year after burning. Cold events were 

 observed on 42 percent of the days on the Htter surface 

 and 26 percent of the days on the burned surface from 

 May through September. Only two CE's were obser\-ed on 

 the litter surface in 1980 and none on the burned surface. 

 Climatic conditions and vegetation regrowth were the like- 

 ly causes of reduced CE's in 1980. 



In the shelterwood. average maximum surface tempera- 

 tures of exposed mineral soil were significantly lower— 5 

 to 34 °F— than temperatures of the litter for 75 percent of 

 the months over the 3 years. Average maximum tempera- 

 tures on the mineral soil surface never exceeded 100 °F. 

 Difference betvveen the litter and mineral surfaces was 

 least in May and October and greatest in July (fig. 10). 

 Hot events on the litter occurred from 14 to 25 percent of 

 the days, but no HE's occurred on the mineral soil surface 

 during the measurement period. Average minimum tem- 

 peratures were 1 to 4.5 °F colder on the litter surface 



11 



