8S FOREST DISTEIBUTIOX 



In the previous eases the percentage composition was in 

 terms of volume estimates; in this it is in terms of the forested 

 areas. In neither case does it give more than a general impres- 

 sion of the relative importance of each species. The figures on 

 this area are with reference to the "type" as it is called by the 

 Forest Service, which means practically the same as the terms 

 society and association in the ecological sense, as where species 

 in pure or mixed stands assume certain characteristic aspects 

 under the control of climatic and physiographic influences. 



In this case it wiU be seen that the leading species are 

 lodgepole pine, Douglas spruce, larch and yellow pine. The 

 larch is confined chiefly to the western side of the section, and 

 to northern slopes and creek bottoms. The yeUow pine, often 

 mingled with Douglas spruce, occupies the southern slopes but 

 with its lower limit at iOOO to 5000 feet elevation. The lodge- 

 pole is found in dense and extensive stand at high elevations 

 along the main range of the Rockies. Pinus manticola and Abies 

 grandis are rare in this section and are found only in isolated 

 localities ; however, limited stands of white pine are to be found, 

 as in the upper end of the Blaekfoot valley close to the Divide, 

 on the Clearwater and elsewhere. AVhere the moisture is suffi- 

 cient in the soil, that of the atmosphere seems deficient or the 

 temperatures too low. For the most part this section seems to 

 be beyond the easternmost limits of the white pine, grand fir, 

 western hemlock, arbor vitae and western yew. 



The eighth division of the Roek^i' ilountain forest will here 

 be called the Sun River Section. Its western margin lies along 

 the continental c rest from the Canadian boundary to the 47th 

 parallel in a strip 20 miles or less in width. It lies on the east- 

 ern slope of the Divide in the narrow timbered zone between the 

 mountain ridge and the prairie foothills. Its northern portion 

 includes a part of Glacier National Park. The Sun River Valley 

 is heavily timbered, but the Teton and ^Marias Rivers traverse 

 elevated plains and prairies. 



