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1905] WHITFORD—FORESTS OF FLATHEAD VALLEY ces 
RAINFALL. 
The greatest danger to trees is an excessive loss of water, and 
therefore the rainfall of a region is very important. It will be pointed 
out later how the conservation of this water supply influences the 
character of the forest. Other things being equal, the greater the 
amount of rain that reaches the earth, the more luxuriant the vege- 
tation. The mean monthly and annual rainfall for Kalispell, Colum- 
bia Falls, Seattle, and Marquette are as follows, the amounts being 
given in millimeters: | 
TABLE II. 
Stations Jan. | Feb. | Mar.|April | May | June | July | Aug.| Sept.) Oct. | Nov.} Dec, |Ann’l 
Malispell.... oi.c ceo 24 25 161 ax | 66} a7 | 33 28} 50 18} 49] 35] 415 
Columbia Falls...... 48 38 301 a3) 68 72 a7 | Sr] 68) ged Sa} 30 | Sas 
Marquette. ei cs. 4 52 45 47 5x 76 89 77 73 99 | 83] 69] 62 | 823 
ORs oe Bos orth tir 94 79 | 82 86 | 40 17 14 | 45 76 | 143 | 158 | 945 
The difference in the amount of rain on the west and east sides of 
Flathead valley no doubt explains the difference in the types of vege- 
tation in these two situations. It has already been shown that there 
is only a slight difference in the amount of heat at the two situations. 
It is very probable that the other elements of climate—light and 
velocity of wind—are about the same for the two places, although 
there are no data to prove this. It must be remembered that the 
towns are only thirteen miles apart, but the difference in rainfall is 
128™™, It is believed that this difference is sufficient to make a 
forest vegetation at Columbia Falls and only a prairie vegetation at 
Kalispell. Kalispell is well out in the valley, while Columbia Falls 
is at the base of the mountains. The rain-bearing winds from the 
west sweep across the high mountains west of the valley, where they 
lose a considerable portion of their moisture, and then descend into 
the valley where the higher temperature they encounter enables 
them to hold more moisture. This is liberated, however, when the 
winds bank up against the cool mountains east of the valley. Thus 
the west side of the valley probably has a rainfall of 4oo™™ or less 
and is not able to support tree growth except along streams; while 
the east side has a rainfall of from 400 to 543™™, a sufficient quantity 
