118 IU'LLETIX 1233, U. S. DEPARTMENT OF AGRICULTURE. 



Table 37. — Snow on the ground under various conditions of exposure, winter 



1910-11. 



[ifean snow depth, inches.] 



Station No. 



Tvpe. 



Xovem- Decem- 

 ber, ber. 



Janu- 

 ary. 



Febru- 

 ary. 



March. 



April. 



May. 



F-l . . . 

 F-2... 

 F-3... 

 W-C . . 

 W-Al. 

 W-A2. 

 W-D.. 



Control, open ridge 



South-slope western yellow pine 



Canyon spruce 1 " 



Open east slope 



North-slope Douglas fir 



South-slope Douglas fir 



Higher spruce bench 



0.2 



, 2 



.5 



4.1 



13.4 



.6 



11.8 



0.6 

 . 5 



1.5 

 10.4 

 17.1 



4.2 

 16. fl 



0.1 

 .1 

 .6 

 20.0 

 23.5 

 5.0 

 24.6 



3.5 

 3.5 

 3.0 



20.3 



21.2 



.9 



24.5 



1.1 

 l.fi 

 6.2 

 26.1 

 36.4 

 8.8 

 44.5 



0.6 



.6 



1.7 



9.2 



2x4 



.1 



36.3 



0.0 

 .0 

 .0 

 .0 



3.4 



.0 



13.8 



i The ground is the lower edge of a northeasterly slope. 



The precipitation in various forest types within the range of this 

 study may now he considered, as shown in Tahle 3S. For the control 

 station tne complete record to the end of 1917 is used. For other 

 stations having an unbroken record from 1910 to 1917 the same 

 months are eliminated as are missing from the record of the control 

 station. When the compared record is considerably broken, all that 

 is available is used. 



In the Pikes Peak series (C-l, M-l, F-l, L-l) the seasonal varia- 

 tions are very similar to those at the control station. The total 

 amount of precipitation for the year or any shorter period increases 

 fairly regularly with increased elevation, except that in the step from 

 the Plains type to the yellow pine type the increase is generally larger 

 than elsewhere. This, it is thought, may be due to the exposure of 

 the Plains station, which is nearly always subject to north and east 

 winds during precipitation. These winds make it more difficult to 

 secure a complete catch. The yellow pine type for almost the entire 

 winter period, moreover, shows more precipitation than the much 

 higher control station. Xo adequate explanation of this can be 

 one red. 



The yellow pine types of the Black Hills and of southern Colorado 

 (D-l and P-l, respectively), which support yellow pine stands of far 

 better development than those of the Pikes Peak region, have the 

 benefit of a much greater total precipitation; but this excess is almost 

 wholly outside the growing season. It may be said that the heavier 

 winter snows are of direct benefit to seedlings, and that they protect 

 the older trees by preventing the freezing of the soil. If, however, 

 the low rainfall in southern Colorado during April, May, and June is 

 considered, it is readily seen, as has been pointed out by Pearson (IS), 

 that the moisture of winter snows may not hold over till summer and 

 hence can not directlv affect the rate of growth. In the Black Hills 

 it probably does not hold over, but melts early at that low elevation, 

 but the spring precipitation is itself abundant and undoubtedly is an 

 important supplement to that of the growing season. Nevertheless. 

 in the search for conditions which may influence the growth of all 

 sp< fie- probably none has been found which is more important than 

 the winter deficit of precipitation in the Pikes Peak region, when con- 

 sidered in connection with high wind- and atmospheric dryness. 



One hundred miles farther north, in a similar topographic position 

 (Station F 17), this winter deficit i- far less apparent, though the 

 high precipitation for this station may possibly he duo to purely 

 local conditions which encourage a transport of snow from the high 

 hill- round about. 



