16 



with that farther south, several species typical of the Pacific coast meet 

 the Rocky Mountain trees, and a great diversity in the composi- 

 tion of the forest is the result. The coast species, which here extend 

 eastward to the Rocky Mountains, are western white pine, giant ar- 

 borvitse, lowland fir, western hemlock, and probably the coast form 

 of Douglas fir. Associated with them, either as separate types or in 

 mixture, are yellow and lodgepole pines, Engelmann spruce, alpine 

 fir, and the Rocky Mountain Douglas fir, all of which attain their 

 greatest importance in the Rocky Mountains. 



The most characteristic forest types in this region are an alpine 

 fir type, a white pine type, a lodgepole pine type, and a yellow pine 

 type. 



The alpine fir type occupies upper slopes and high ridges, and 

 hence is not continuous. It is composed chiefly of alpine fir, with 

 white-bark pine, Engelmann spruce, and, near its lower limits, a mix- 

 ture of Douglas fir, lodgepole and western white pines, western larch, 

 and aspen. The stand is open and parklike at high altitudes, but be- 

 comes dense as it descends, and gradually changes into the next type. 



The white pine type occupies protected situations and moist soils 

 with heavy stands of western white pine mixed in widely varying 

 proportions with western larch, giant arborvitoe, Douglas fir, lodge- 

 pole pine, lowland fir, and western hemlock. Lowland fir is often a 

 serious menace in this type through its aggressiveness in restocking 

 burns to the exclusion of more valuable trees. Western larch predom- 

 inates over limited areas, and in many places forms an important 

 type. 



The lodgepole pine type is doubtless in most cases a temporary type 

 which has succeeded western white pine after fires, and will eventually 

 revert to white pine or other more tolerant species if fires are kept 

 out. The young stands are dense and crowded, but as they mature 

 they become more open. The forest is largely pure lodgepole pine, 

 especially on poor, shallow soils ; but with deep and moist soils there 

 is often a large proportion of Douglas fir, lowland fir, larch, and En- 

 gelmann spruce in mixture. 



The characteristic yellow pine type is an o]Den, pure forest of yellow 

 pine and occupies relatively dry situations at low altitudes. In moist 

 localities, however, the forest becomes dense and contains Douglas fir, 

 lowland fir, western larch, and lodgepole pine in mixture. In 

 swampy situations at low altitudes there is often a " cedar swamp " 

 type, composed of giant arborvitse, either in pure stands or in mixture 

 with white pine, larch, hemlock, Douglas fir, or lowland fir. 



The climate of this region is humid, with abundant precipitation 

 during the growing season, sometimes as much as 40 inches. Daily 

 and seasonal ranges of temperature are not, as a rule, excessive, and 



[Cir. 150] 



