THE FOREST AND THE: PRAIRIE. 249 



The Forest and the Prairie. 



Harry Nichols Whitford. 



Plants may be divided into two groups, herbaceous and woody. In 

 the former the part above ground dies in the unfavorable season; in the 

 latter the part above ground does not die annually. These two general 

 forms may be subdivided. For example, the herbs may be divided into 

 annuals and perennials, and the woody type may have the form of the 

 shrub, vine, or tree. The climate of the greater part of the state 

 of Montana is more favorable to herbaceous than to arboreous plants. 

 The portion of the state east of the Rocky mountains is primarily a region 

 where the moisture conditions will not permit trees to grow. However, 

 there are certain parts in which the rainfall is sufficient in quantity to 

 favor the growth of trees. The northwestern portion of the state, em- 

 bracing the Flathead valley and the mountains on each side, is an ex- 

 tremely favorable place for the production of forests, but parts even of 

 the Flathead valley are incapable of supporting trees. On one side of 

 the valley, the prairie side, the rainfall is less than sixteen inches. The 

 forest side has a rainfall of about twenty-one inches. 



In order to understand why trees are confined to certain regions, it is 

 of extreme importance to know what functions they perform and how 

 the conditions in which they grow affect the work they do. 



The tree absorbs water. It does this through its root system, and 

 the greater the root system, the greater the power of absorbing water. 

 The tree with an extensive and deep root system can live in drier situa- 

 tions, other things being equal, than the tree with a shallow root system, 

 for its roots come into contact with more water in the soil, and in some 

 cases may reach to the underground water level. In the latter case it is 

 not so dependent on the amount of rainfall. Where the underground 

 water level is near the surface, trees with shallow roots have as good a 

 chance to get water as trees with deep roots. To illustrate these two 

 points, compare the bull pine and the silver pine. The former has a 

 deep and wide spreading root system. It can grow in much drier soils 

 than the latter, which, on the other hand, has a shallow root system. It 

 is, as a rule, confined to those situations where there is a great deal of 

 water in the soil. Again, the root system of a tree serves to hold it in 

 place. Those trees with deep root systems cannot be blown over so 

 easily as those trees with shallow root systems. In the Flathead valley 

 it is not an uncommon thing to find silver pines lying prostrate with 

 almost their entire root system exposed, while other trees in the same 

 situation are able to resist the wind because they have deeper root sys- 

 tems. 



The tree is using water continually for three purposes: 



1. Small quantities are used to supply the new growth that is added 

 to the tree annually. 



