THE FORESTS. 17 



forest of entirely different aspect achieves dominance over the whole 

 area. Along the shores of Flathead Lake are forests of fir, larch, 

 and spruce, mixed with some hardwoods, which can be traced back 

 to the beginnings of pines and grassland. 



Slide-rock areas are common everywhere in this region. They 

 vary from the clear gray of freshly broken rock fragments of the 

 talus to forested slopes in all stages of development. Thus the rocks 

 support a lichen crust which is gradually replaced by mosses. Under 

 disintegrating influences affecting the surface layers of the rock and 

 the accumulation of vegetable matter a foothold is given for small 

 herbs, and then for bushes, and at last for the forest. 



Similarly, changes are slowly transforming ponds into bogs and 

 bogs into solid ground, with corresponding changes in the plant 

 covering. River deltas and bars first occupied by the sand-bar 

 willow increase in height and area by the augmenting influence of 

 the willow itself, giving place to cottonwood, alder, and birch, and 

 finally to spruce and other species. 



Examples might be cited indefinitely, illustrating the inarch of 

 forest development through changes by insensible degrees which 

 pass unnoticed from generation to generation. The tendency is 

 toward a climax type, which, so long as the climate does not change, 

 Avill maintain a balance among its constituent species, among which 

 some will be dominant and others dependent. In the climax forest 

 they will always be shade-enduring species, for so long as the stand 

 is open, as it must be with species intolerant of shade, just so long 

 may other and more tolerant ones enter. Traits of a species which 

 give dominance in a forest society may be rapid growth in height, 

 tolerance of shade, simplicity of soil requirements either of these 

 or all of them taken collectively. But even in a climax forest there 

 is no truce to the warfare ; there is merely balance of the contending 

 forces. Disturb this balance by the removal of a part, and battle is 

 again joined, with the advantage to one side or the other. 



Looking, then, into the distant future, we might expect changes to 

 come which, if left untouched by human agency, would end in com- 

 plete forest covering of the land and growth in density as well as in 

 area. Such changes, however, are in their nature and progress like 

 geological changes of erosion and deposition, of elevation and sub- 

 sidence, always toward a more or less certain and definite conclusion. 

 But with the forests the hand of man can affect the result and is most 

 sure to do so. 



