FOREST TYPES IN CENTRAL ROCKY MOUNTAINS. 



49 



3. The lodgepole-pine type, wherever found, seems to be charac- 

 terized by very low winter temperatures and also by growing-season 

 temperatures considerably lower than those of the control station. 

 It is believed that the low winter temperatures of this type are always 

 accompanied by heavy snowfall, which, at least at the southern 

 Wyoming station, arrives so early as to prevent deep soil freezing. 

 These facts suggest that the most obvious requirement for reproduc- 

 tion of lodgepole pine is a winter climate of such low temperatures 

 and with such an abundance of snow that the evaporation factor is 

 essentially nullified. This would seem to explain the absence of 

 lodgepole pine from the Pikes Peak region, but not its ability to 

 grow there when planted. As has been shown by the physiological 

 studies, it is more probable that in the Rocky Mountains it is crowded 

 out of its normal temperature zone by demands for moisture which 

 can be met only at elevations where the snowfall is heavy and well 

 conserved throughout the winter. The mean temperatures indicated 

 bv these data are: 



Locality 



Highest. .. 



Lowest 



Totai range 



Growing 



i 



season. 





° F. 



F. 



54.79 



36.37 



52.37 



34. 43 



50.30 



31. 55 



49.94 



32. 19 



4.85 



4. 82 



Western slope. 

 Continental Divide. 

 Frascr Basin. 

 Southern Wyoming. 



It will be noted that these maxima overlap somewhat into the zone 

 of Douglas fir temperatures. It will also be noted later that the 

 temperatures enjoyed by lodgepole pine come within the range of 

 temperatures enjoyed by spruce. 



4. The single spruce station listed in this table (W-G) shows a 

 January temperature scarcely lower than the Douglas fir station 

 (W-Al; of tne same region, but for the remainder of the year the 

 high spruce type is much cooler. The annual and growing-season 

 means of this station are also remarkably close to those of the timber- 

 line station (F-16, Table 8) of the Pikes Peak region, the two being 

 at almost the same elevation, and the former not more than 500 feet 

 below timber line for its locality. This suggests that an annual mean 

 of slightly less than 32° F. may be the limiting factor for all forest 

 growth in the central Rockies. It is suspected, however, that such 

 a limitation is placed upon growth only indirectly if at all. 



All of the spruce temperatures may be summarized as follows: 



Highest 



Lowest 



Total range 



Crowing 

 season. 



5 /-'. 

 55. 93 

 52. 44 



51.0!,' 



49. 53 



iv 96 

 ('.. 97 



Year. 



° F. 



» 38. 77 



Locality. 



32. 13 

 31.63 



7. 1 I 



Fremonl , canyon type. 



Fremonl , middle zone 



ml . canyon type. 



ip, near timber line. 

 Fremont, timber line. 



Average of ground and air conditions at F-3. 

 73045°— 24 4 



