40 



BULLETIN 1364, U. S. DEPARTMENT OF AGRICULTURE. 



have been strikingly affected by variations in rainfall from year to 

 year. This is graphically shown in Figure 7. It must be remem- 

 bered in connection with this chart that the chief plantings were in 

 Utah, with western yellow pine, and usually at fairly low elevations. 

 The general rising trend of the curve showing success is due to two 

 causes: (1) Younger plantations are more likely to show success 

 than older ones, other things being equal; and (2) better planting 

 sites have been chosen during recent years and success has been 

 actually better than before. 



Figure 7 further shows that it is much more logical to attribute 

 the successes to abnormally heavy rainfall than the failures to 

 drought, as the dry years are much nearer the normal than such wet 

 years as 1913 and 1914. It is evident that planting must be confined 

 to sites having normally good moisture conditions in order to be 

 successful. By planting at high elevations, better conditions in this 

 regard can be obtained. 





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Fig. 7.— Rainfall for June and July (Utah State means) in relation to success of administrative plantations 

 from 1910-1919, based on per cent of total area planted which was classed as successful in 1919. 



In Ephraim Canyon on the Manti National Forest the rainfall at 

 the mountain crest (10,000 feet) in June and July averages 2.28 

 inches (1915-1920); in the aspen or Douglas fir type (8,750 feet) it 

 is virtually the same, 2.24 inches; in the oak-brush type (7,200 feet) 

 it is 1.7 inches; while in the valley at the foot of the mountain (5,500 

 feet) it is 1.08 inches. Add to this the effect of the late melting 

 snow at high elevations, and it is evident that soil-moisture condi- 

 tions are decidedly superior in the upper region. On the more se- 

 vere sites at low elevations, success can be expected only in excep- 

 tional years, the same being true of natural reproduction in these 

 places. 



The seasonal distribution of rainfall through the year is a factor 

 that is believed to exert a profound influence upon the success of 

 plantations in the intermountain region, and is probably the most 

 powerful single factor in explaining the degree of failure experienced 

 in tins regioo in comparison with other regions equally arid when 

 annual or even total summer rainfall is considered. It is impossible 

 to show detailed rainfall figures for planting areas or even for general 



