132 



BULLETIN 1333, U. S. DEPARTMENT OF AGRICULTURE. 



(3) The winter temperatures at middle and lower elevations in 

 the Pikes Peak region are rarely very low; relatively warm, strong 

 winds occur frequently from January to March; and evaporation 

 stresses are very telling, except at nigh elevations where the air 

 temperature rarely goes higher than 32° F. The precipitation also 

 during the winter months is very low. Clear weather and the lack 

 of material for evaporation result in great dryness of the atmosphere. 

 Another effect of the lack of snow is seen in the early and deep freez- 

 ing of the soil, except on well-insolated exposures. In the main, 

 then, trees are subjected to conditions which induce rapid transpira- 

 tion, and at the same time are cut off from their moisture supply 

 by the freezing of the moisture in the soil. Obviously, these condi- 

 tions are not a less severe strain upon the well-established tree than 





















































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Fig. 10.— Summary of the several conditions in the various forest types. 



upon the seedling which may secure protection through shading or 

 through a temporary snow blanket. 



It is believed that these winter conditions, rather than the poor 

 quality of the soil, delimit the growth of all forest trees in the locality, 

 and produce a scrubby stand which on some sites has apparently 

 reached its limit at a height of 40 feet or less. 



(4) The extension of observations to other localities both north 

 and south of the Pikes Peak region indicates a less complete develop- 

 ment of most of the unfavorable features of climate. To the south, 

 to be sure, the spring drought is more pronounced and may possibly 

 destroy seedlings of the preceding season. The summer rainfall is 

 no more abundant, but the fall drought is of less duration; a snow 



