SHORE VEGETATION OF FLATHEAD LAKE, MONTANA 



GERTRUDE P. NORTON 



Biological Station, University of Montana, Missoula, Montana 



The plant life found on the beach of a large body of water 

 between the lines of high and low water forms a very distinct 

 plant association. It varies little for long periods of time, and 

 yet is only a stage in the development of the vegetation. It con- 

 sists of plants that are able to survive under adverse conditions; 

 such as extreme drought, submersion, action of winds and waves, 

 and the scraping of ice, logs and floating debris at times of high 

 water. 



The difference in level of Flathead Lake, Montana, at times 

 of high and low water is very great. In 1916 the high water 

 mark was reached on July 4. It lacked about four feet of the 

 high water mark of 1894. The total rise from June 16 to July 

 4 was 60.5 inches. The water began to fall on July 5 varying 

 from 1 to 5 inches a day. On August 3, there had been a total 

 fall of 89 inches. For the entire season the difference between 

 high and low water mark was 160 inches. 



From the record of this season it can be seen that the shore 

 plants had no chance to begin growing until midsummer. Some 

 were killed from remaining too long under water. Every high- 

 water year many acres of low-lying meadow and swamp-thicket 

 are submerged. 



The shore successions are of both xerophytic and hydrophytic 

 types, the same kind of climax forest results from either. Where 

 there is not enough moisture for a forest, a prairie formation is 

 developed, as on the south and west sides of the lake and part of 

 Wild Horse Island. 



The altitude of Flathead Lake, is 2916 feet; the plant life is 

 that of the Transition Zone. The prevailing type of forest is 

 the Douglas fir — western larch forest. Beside these dominant 



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