28 Forest Club Annual 



tion, and the belts are plant zones. There are various sorts of 

 zonation, for instance we know of the great transcontinental 

 life zones parallel with the equator. Climatic factors are most 

 important in the production of such zones. In other words 

 differences in latitude with the consequent changes in climate are 

 mostly responsible for this phenomenon. When we come to 

 mountain zones although the individual zones are much nar- 

 rower than the above yet we find that essentially the same 

 factors, i. e., climatic factors, have been powerful in their pro- 

 duction. But here the climatic differences are initiated by 

 changes in altitude as against latitude in the former case. The 

 various edaphic factors are probably of much more importance 

 in the production of mountain zones than of continental zones, 

 since these factors are much less stable on steep mountain sides 

 than over wide stretches of relatively level country. But still 

 the result is practically the same except for the mere difference 

 in width. 



It was early in the eighteenth century that Tournefort in 

 his studies of mountain vegetation first recognized zonation. 

 He noted that on Mt. Ararat many Armenian species were found 

 at the base of the mountain, while on the slopes above there 

 were many species of southern Europe. Still higher plants 

 similar to those of Sweden were found, and still above these 

 the vegetation was very similar to that of Lapland. 



So in the Rocky Mountains we find vegetation at successively 

 higher altitudes very similar to that met as one travels from the 

 United States to the polar seas. Writers on the subject have 

 made various classifications of mountain plant zones, and while 

 these differ in details, they are in the broad outline very similar. 

 For the present I shall use a rather simple and general classi- 

 fication and hence one that can be rather widely applied to the 

 region under discussion. Throughout the Rocky Mountains 

 the following zones can be quite clearly delimited: 



1. The Plains Grass Zone. 



2. The Foothill Forest Zone. 



3. The Mid-Forest Zone. 



4. The Subalpine Forest Zone. 



5. The Alpine Desert Zone. 



It is seen from the names of the zones that in reality here 

 we have a single wide belt, which is essentially forest, bound above 

 and below by desert zones. The large forest zone is divided in 

 turn into the three secondary zones as indicated above. It 

 must not be supposed that these regions are perfectly distinct 

 at all places. On the contrary, they intergrade almost insensibly 

 in many places. However, the upper and lower limits of the 



