FOREST TYPES IN CENTRAL ROCKY MOUNTAINS. 117 



Although the individual years do not vary in precipitation much 

 more widely than in other conditions, the months do. Thus a long 

 record seems necessary to establish even an approximate "normal" 

 precipitation for a given month. The addition of the 1918 record to 

 the record for the eight preceding }^ears created two new extremes, 

 namely, a new high for January and a new low for May, and the 

 growing-season total was the highest of record except for 1914. 

 Again, the year 1921, through July, created three new monthly 

 maxima, and the last 12 months of record show a total of 34.38 inches. 



Comparative 'precipitation. — No serious effort has been made to 

 compare the precipitation in the several forest types in the vicinity 

 of the Fremont Station, for it has been assumed that, so far as 

 topography might influence the actual fall, differences would be com- 

 pensating over any long period. It is perfectly evident that one spot 

 may at one time receive from summer rains much more moisture than 

 another only a few hundred feet away, and such a variation may not 

 be compensated for a long time. However, where the difference is 

 marked, the excess at a given point is likely to be largely wasted in 

 surface run-off. 



From March, 1910, to February, 1912, at three stations within a 

 radius of a few hundred feet gages were maintained on towers so 

 situated that there was almost no interference by branches of trees, 

 but with varying degrees of protection from wind. Table 36 gives 

 the mean annual catches that were recorded. 



Table 36. — Precipitation catches at three stations, 1910-1912. 



F-1A. 

 F-2A. 

 F-3A. 



Control, open 



South-slope western yellow pine . 

 Canyon spruce 



Inches. 

 19.25 

 18. 95 



20.12 



For the period April, 1916, to February, 1917, a gage on the ground 

 at Station F-9, under dense cover of fir and spruce and less than half 

 a mile from the control station, gave a catch of 22.73 inches as com- 

 pared with 19.32 inches at the control station. The excess under 

 canopy was very great from certain rains on account of some spruce 

 branches, but with snow a deficit was generally created by these same 

 branches. A very different result would doubtless have been obtained 

 2 feet farther from the tree whose branches most directly influenced 

 the path of falling rain or snow. 



If the amounts of snow on the ground in the different types are 

 compared for the late spring period when such snow may represent 

 an asset for the coming growing season, the greatest contrasts may be 

 obtained. It is not the purpose of the writer to discuss this feature 

 here. Moreover, because of lack of adequate data, it is not possible 

 to give any numerical weight to the retained precipitation of the 

 various forest types here studied. However, the data given in 

 Table 37, reproduced from the preliminary report on this project, 

 indicate the importance which must be attached to this subject in 

 considering precipitation data. 



