The effects of exposure on minimum temperatures of the soil surface differed with 

 shading. Minimum temperatures of unshaded surfaces were lower on southwest exposures 

 by 0.7° F. (a = 2.2) at the lower elevation, and by 5.6° F. (a = 4.0) at the upper 

 elevation. In contrast, minimum temperatures of shaded surfaces were lower on northeast 

 exposures by 1.0° F. (o = 1.8) at the lower elevation and 1.6° F. (a = 2.0) at the upper 

 elevation. 



The effects of elevation on surface temperature of the soil are more pronounced 

 than those of exposure. Maximum and minimum temperatures were highest at the 7,100-foot 

 elevation with one exception. Inexplicably, the unshaded surface on northeast exposures 

 was colder at the lower station than at the upper. Otherwise, the differences in 

 temperature between elevations are similar on the two exposures. Stations at the 7,100- 

 foot elevation differ from those at 8,200 feet by: 



SOIL SURFACE 



Shaded 



(°F.) (a) 



Unshaded 

 (°F.) (a) 



Average maximum tempevatupe 



Southwest exposures 

 Northeast exposures 



Avevage minimum temperature 



Southwest exposures 

 Northeast exposures 



8.4 (3.0) 

 7.9 (3.1) 



4.4 (1.7) 

 4.7 (2.0) 



12.4 (6.7) 

 11.4 (7.5) 



2.9 (2.8) 

 -2.4 (3.5) 



Soil temperature at various depths followed a seasonal curve similar to that of 

 air temperature, but was more subdued (fig. 7). At all three depths (20, 50, and 100 

 cm.), the average daily temperature in early May was just above freezing. As the grow- 

 ing season progressed the temperature gradually increased, reaching a maximum in late 

 July and early August. The temperature at all depths had dropped to less than 40° F. 

 by the end of October. As was expected, temperature response lagged as soil depth 

 increased. The temperature at the 20-cm. depth peaked in late July and began to drop 

 thereafter. The temperature at the 100-cm. depth peaked about 1 week later but did not 

 decrease more than 1° F. until the first of September- -about 1 month after the drop be- 

 gan at the 20-cm. depth. 



From May until mid-August, temperatures at a depth of 20 cm. averaged 2° to 4° F. 

 above those at 50-cm. depth. A temperature reversal occurred in late August. From 

 then on, the temperatures at a depth of 50 cm. were as much as 4° F. warmer than those 

 at the 20-cm. depth. Temperatures at the 50-cm. depth remained 2° to 5° F. warmer than 

 those at the 100-cm. depth until about mid-September. The temperature crossover here 

 took place in early October. At that time, the 50-cm. depth became colder than the 

 100-cm. depth. The year-to-year variation in soil temperature decreased with depth. 

 At all depths, yearly variation was greatest in late summer. 



14 



