FORK.-T DlsTKIIiTTlON 



In the previous cases the percentage composition was in 

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

 In neither < ase 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 !>y 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 will he 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 yellow pine, often 

 mingled with Douglas spruce, occupies the southern slopes hut 

 with its lower limit at 4000 to 5000 feet elevation. The Lodge- 

 pole is found in dense and extensive stand at high elevations 

 along the main range of the Rockies. Finns moulicola and Altic* 

 </r<ii><Hs are rare in this section and are found only in isolated 

 localities: however, limited stands of white pine are to he found. 

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

 on the ('learwater and elsewhere. Where 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, 



rn hemlock, arbor vitae and western yew. 

 The eighth division of the Rocky Mountain forest will here 

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

 the continental crest from the Canadian boundary to the 47th 

 parallel in a strip 20 miles or less in width. It li<-s on the east- 

 ern slope of the Divide in the narrow timbered /one between the 

 mountain rid'jv and the prairie foothills. Its northern portion 

 include ;i part of (Ilacier National I'ark. The Sun River Valley 

 is heavily limlercd. but the Teton and Marias Rivers traverse 

 elevated plains and prairies. 



