FOREST TYPES IK CENTRAL ROCKY MOUNTAINS. 47 



The observations at all outlying stations, it is believed, have been 



made at an elevation of about 5 feet ahove the ground as compared 

 with 20 feet for the control station, but, as has been shown, this factor 

 can not materially affect the mean temperature for any month. An 

 examination of such data as are readily available on the daily range 

 of air temperatures for other localities shows that a range of about 

 20° to 22° is characteristic throughout the region under discussion, 

 except in the Nebraska sandhills. The relation of maxima ami 

 minima to means will be, therefore, almost the same as the relation 

 at the control station. 



Air temperatures compared by forest types. — 1. The yellow pine 

 station in southern Colorado shows less excess over the control sta- 

 tion than does a station 400 feet distant, and less than the Monu- 

 ment station at the foot of the Pikes Peak series, if the comparison 

 is made for the whole year. For the growing season, however, the 

 southern Colorado station is slightly warmer than the local yellow 

 pine type, but not equal to the Monument station. In both south- 

 ern Colorado and the Black Hills yellow pine endures much lower 

 winter temperatures than occur at any but the highest elevations in 

 the Pikes Peak region. The fact must not be lost sight of, however, 

 that these low temperatures are endured in the presence of a deep 

 blanket of snow which may largely prevent soil freezing. 



All of the data for the western yellow pine sites may be briefly 

 summarized and reduced to absolute temperatures, in the order of 

 growing-season temperatures, as follows: 



Localitv. 



Growing 



Year. 



season. 





•F. 



°F. 



63.60 



43.39 



61.56 



43.96 



60.88 



41.69 



158.65 



42. 23 



s 56. 65 



39.98 



54.05 





9. 55 



3.98 



Highest 63.60 43.39 Black Hills. 



" Pikes Peak, M-l. 



Southern Colorado. 



Fremont, south slope. 



Fremont, ridge. 



Lowest 54.05 Fremont , east slope. 



Total range 



1 Averaging ground and air conditions. 



3 Based on May, July, and October differences. 



It is then seen that the Black Hills station, in a low-lying region 

 where other forest species are practically excluded, has the highest 

 growing-season temperatures of any of the western yellow pine types, 

 and with this condition and fairly high rainfall the species reaches 

 optimum development, at least in reproduction. Where the low 

 growing-season temperatures of yellow pine types are found Douglas 

 fir and limber pine also appear in considerable proportions. 



Establishment of yellow pine by planting has been successfully 

 accomplished in the Nebraska sandhills, where the mean temperature 

 for the growing season is in excess of 70°, and for the year is nearly 

 48°. The foimer is about 7° is excess of the Black Hills yellow pine 

 type. These conditions, however, not only have prohibited natural 

 extension of pine to tins region, but have caused considerable lo 

 in plantations; furthermore, they have precluded direct seeding. 

 Although, of course, all the conditions which accompany these tem- 

 peratures must be referred to, still the more this matter is studied, the 

 greater is the conviction that temperatures do very largely control 

 the distribution of species, although the air temperatures as measured 



