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THE FORESTS OF THE FLATHEAD VALLEY, MONTANA.* 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
»XVIT. 
HARRY N. WHITFORD. 
(WITH MAP AND TWENTY-THREE FIGURES) 
INTRODUCTION. 
THE factors concerned in the grouping of plants are classified by 
SCHIMPER? as climatic and edaphic. When the climate of any region 
is such that a particular form of plant is favored, in most instances 
it gives character to the vegetation. For example, in the eastern 
United States the climate favors the tree form and gives rise to a 
“forest formation.” If the grass form predominates, however, a 
“prairie formation” is the result. Again, if the climate be such that 
the cactus form gives the tone to the landscape, the “desert formation” 
is developed. .Two such formations are shown in fig. 1, which is a 
view of a portion of the Flathead valley looking west from a high 
mountain. In the distance on the west side of the valley is a prairie 
formation; on the east side is a forest formation. 
However, if one stands on a mountain top and looks down into 
these formations, he will observe that isolated areas in the forest do 
not contain trees, but may have a prairie, a swamp, a clearing, or a 
heath. The prairie formation may contain forests along streams or 
on protected hillsides. Also, in the forest formation there may be 
areas occupied almost exclusively by one, two, or more species of 
trees; while at a little distance there may be another area with entirely 
different trees. In other words, the composition of the forest 
changes from place to place. To distinguish these local groups 
from the general climatic grouping, SCHIMPER has called them 
“edaphic formations.’ By other authors they have been called 
“plant societies,” ‘plant associations,’ or merely “plant forma- 
This paper is based on work as a collaborator in the U. S. Bureau of Forestry, 
to which acknowledgment is here made for permission to publish. 
CHIMPER, A. F. W., Plant geography upon a physiological basis (translated 
by FISHER) 159-161. 1903. 
1905] 99 
