FOEEST TYPES IX CENTRAL ROCKY MOUNTAINS. 



97 



Extremely low air temperatures in winter may be made more 

 seYere by melting snow in the vicinity, which, as it melts, tends 

 to absorb most of the sun's heat. On the other hand, the snow 

 blanket tends to hold up the soil temperatures and to prevent 

 deep freezing. Thus, although the lodgepole pine type in Wyoming 

 (Station F-11) has a mean air temperature practically equivalent 

 to that of timber line at Pikes Peak, its mean soil temperature is 

 some 5° higher and its winter soil temperature is 11° higher. Again, 

 the high-altitude spruce station at Wagon Wheel Gap has practically 

 the same mean annual air and soil temperatures as the timber line 

 station on Pikes Peak; but while the latter's January soil temperature 

 drops to 15.2° F. the former reaches a low point of only 26.9° F. 

 The difference is due to lack of snow cover at the timber line station, 

 and, similarly, the lack of forest cover gives this station much higher 

 summer soil temperatures. 



In Table 29, both air temperatures and 1-foot soil temperatures 

 have been summarized in such a way as to bring out the contrasts 

 which exist at different seasons, and to show that soil temperatures 

 and air temperatures do not give similar measures of site conditions. 

 The differences between soil and air temperatures are to some extent 

 illustrated in Figures 7 and 8. It must, of course, be borne in mind 

 that the air temperatures given in this table are approximations to 

 the " normals" for the period 1910 to 1918, by comparison with 

 the control station, but that the soil temperatures represent shorter 

 periods, and somewhat different periods for different stations. 



Table 29. — Comparative air and soil temperatures. 



[Soil temperatures in degrees Fahrenheit at 1 foot, corrected for year and growing season by amounts 

 indicated in Table 24; for winter, by one-half o'f these amounts.] 



Station 



Forest type. 



Annual 

 temperatures. 



Growing-season Winter (Jan.-Mar.) 

 temperatures. temperatures. 



No. 



Air. 



Soil. 



Differ- 

 ence. 



Air. 



Soil. 



Differ- 

 ence. 



Air. 



Soil. 



Differ- 

 ence. 



H-2 



Sandhills 



47.47 

 43.96 



42.23 

 39.98 



50.78 

 46.46 



45.76 

 41.52 

 41.20 

 37.94 

 43.42 

 37.53 

 37.28 

 37. OS 

 31.35 

 3& 02 

 38.33 

 32.90 

 33.24 

 38.-56 

 40.32 

 38.34 



+3.31 



+2.50 



+3.53 

 +1.54 



"— i.*75* 



+5.S8 

 -2.05 

 -1.95 

 -1.69 

 -4.41 

 -0.89 



'+6*77" 

 +1.61 

 +6.07 

 -1.80 

 +1.33 



70.81 

 61.56 



58.65 

 56.65 

 54.00 

 56.68 

 55.98 

 56.52 

 56.58 

 55.78 

 54.18 

 55. 95 

 50.98 

 49.53 

 48.96 

 49. 94 

 59.02 

 54.39 



72.37 

 60.70 



58.16 

 55. 5S 

 56.43 

 54.14 

 55. 54 

 51.39 

 50.62 

 4S. 17 

 43.94 

 50.63 

 48.37 

 40. 34 

 49.93 

 49.07 

 53.40 

 52. 81 



+ 1.56 



- 0.S6 



- 0.49 



- 1.07 

 + 2.43 

 -2.54 



- 0.44 



- 5.13 



- 5.96 



- 7.61 

 -10. 24 



- 5.32 



- 2.61 



- 9.19 

 + 0.97 



- 0.87 



- 5.62 

 -1.58 



29. S7 

 29.43 



29.10 

 25.84 



"25*76' 

 22. 67 

 25. 50 

 25.03 

 24.77 

 20.87 

 25.40 



"is." 03* 

 17. 83 

 IS.. Si) 

 27.50 

 23.67 



32.00 

 33.32 



34.02 

 29.19 

 27.90 

 24.12 

 30.98 

 26.36 

 26.16 

 26.97 

 20.19 

 27.92 

 28. 60 

 27.50 

 IS. 36 

 29.80 



_N. Mi 



27.63 



+ 2.13 



M-1 



F-2 



F-12.... 

 F-4 



Western yellow 

 pine. 



do 



do 



Pine-fir 



+ 3.89 



+ 4.92 

 + 3.35 



F-7-S... 

 W-A2... 

 F-15.... 

 F-14.... 



F-9 



"\V-A1... 



F-3 



F-o 



W-F.... 



F-16 



F-11.... 



F-6 



F-13.... 



Fir with pine 



do 



Douglas fir 



do 



Fir with spruce... 

 do 



Engelmann spruce. 



do 



do 



Timberline 



Lodgepolepine — 



Limber pine 



do 



39.69 

 37.54 

 39.58 

 39. 23 

 38. 77 

 35.76 

 38.91 



""32." 13' 

 31.63 

 32. 49 

 41.92 

 37. 01 



- 1.58 

 + S.31 

 + 0.86 

 + 1.13 

 + 2.20 



- 0.68 

 + 2.52 



" + "9." 47 

 + 0.53 

 +11.50 

 + 1.36 

 + 3.96 



In Table 29, certain relations stand out in bold relief, as, for ex- 

 ample, the ability of the soil of well-insolated sites to equal or even 

 exceed the air temperatures during the growing season, although 

 the north slopes and those covered oy the denser stands fail to do 

 this by 2.5° to 10.2°. It is significant that all of the warmer sites 



73045°— 24- 



