4 BULLETIN" 1233, U. S. DEPARTMENT OF AGRICULTURE. 



and that the moisture conditions have been met by this adaptation 

 as the need arose. 



As between spruce and lodgepole pine there is plainly a distinction. 

 The former is evidently uncler no stress to root vigorously, for under 

 the temperature conditions to which it is adapted exhaustion of the 

 surface moisture is a very slow process. Furthermore, according to 

 the present interpretation, the species is capable of coping with a 

 considerable degree of drought. It seems almost certain that lodge- 

 pole thrives best with relatively high temperatures, yet the root 

 development is adapted only to existence in perpetually moist sites. 

 The sluggish germination of lodgepole pine seeds, except when 

 exposed to wide temperature ranges, suggests adaptation to open, 

 exposed situations without other cover. From this and other bits 

 of evidence it may be concluded either that lodgepole pine is a recent 

 migrant to the central Rocky Mountains and is poorly adapted to a 

 region of great atmospheric dryness, or is capable of developing only 

 in the early stage of a succession, when competition for moisture is 

 lacking. 



With these facts and theories as a working hypothesis, it is now 

 intended to examine the environmental conditions for evidence as 

 to the factors which must be controlling in the formation of each 

 forest type. 



THE METHOD OF STUDY. 



The primary data to be presented in this bulletin arc records of 

 climatic and soil conditions in different forest types. The main 

 object of such a presentation must be to show that differences in 

 climatic and soil conditions between the forest types either do or do 

 not exist in sufficient degree to account for the varying phenomena 

 of occurrences and growth. 



As the special data collected by the Forest Service do not cover 

 periods long enough to establish the " normal" conditions of any of 

 the forest types (and by this is meant the average conditions for a 

 period of at least 20 years), and since even the average conditions for 

 a period of 10 years may vary considerably from normals," it is 

 necessary to assume that important differences between forest types 

 are fairly constant, and will be brought to light b} T the consideration 

 of short-period records. Such bases can not be fraught with any 

 serious dangers, moreover, when, as in this case, the forest types fco 

 be compared are in the same general locality, that is, in the path of 

 Ik" same air currents and storm centers. Any considerable separa- 

 tion of the stations, however, especially in a rugged mountainous 

 region, is likely to introduce temporary variations in certain condi- 

 tions which are Hot ''normal," and particularly in those conditions 

 which are most directly influenced by the path of storm centers. 

 Thus at t!ic time of this writing it appears that the storm centers 

 have for some time been passing considerably to the north of the 

 Pikes Peak region, giving that locality unusual westerly winds and 

 leaving il without its usual amount of moisture. Consequently ;is 

 early <m> the end of May an unprecedented shortage of water e.\i^t>. 

 while scarcely 1 00 miles to the north unusually large accumulations 

 of snow are reported. 



Again, the moisture factor is most variably influenced by the 

 restricted character of many of the summer showers; especially are 



