44 THE VEGETATION OF THE UNITED STATES. 



occidentalis, J. pachyploea). Sometimes these two types are equally 

 mingled, or more frequently one of the two is predominant. The 

 species mentioned do not greatly overlap, but occupy different areas 

 within the Xerophytic Forest. With these coniferous trees grow also 

 certain evergreen broad-leaved oaks. In the Great Basin and in Colo- 

 rado the role played by the oaks is a minor one, but in New Mexico it 

 is more important, and in southern Arizona several arborescent species 

 of evergreen oaks are frequently as common as the conifers, or more 

 so. The Xerophytic Forest also contains numerous conspicuous shrubs 

 of different types {Cercocarpus, Cowania, Artemisia, Ephedra, etc.), 

 as well as such succulent and semisucculent plants as the yuccas and 

 agaves, and conspicuous bunch-grasses and other perennials of inter- 

 mittent or seasonal activity. 



Northwestern Hygrophytic Evergreen Forest. — This forest occupies 

 the coastal region of Washington, Oregon, and extreme northern 

 California, and an isolated portion of it lies on the western slopes of 

 the Cascade Range in Oregon. This area exceeds any portions of the 

 Mesophytic Evergreen Forest in density of stand and in the stature of 

 the trees, which very frequently exceed 100 feet in height. The 

 heavily shaded floor of the forest is covered with fallen trunks and 

 limbs, overgrown with mosses and hepatics, and underlaid by a deep 

 bed of humus. The deciduous trees are few and small, but a number 

 of evergreen ericaceous shrubs are common on the floor of the forest, 

 as are also ferns and large-leaved herbaceous plants. 



The density, tall stature, and vigorous activity of the Hygrophytic 

 Forest give it a very distinctive physiognomy and betoken a set of 

 environmental conditions unlike those of the Mesophytic Forest, in 

 accordance with which it possesses a number of distinctive tree species. 

 The tree which is of most general occurrence throughout the area is 

 the Douglas fir {Pseudotsuga m'wcronato) , which is also found far beyond 

 the limits of this forest. It is accompanied in nearly equal admixture 

 in many localities by the black hemlock {Tsuga mertensiana) . Other 

 species common in this forest are the Sitka spruce {Picea sitchensis), 

 white fir {Abies grandis), giant cedar (Thuja plicata), amabilis fir 

 (Abies amabilis), noble fir {Abies nobilis), redwood {Sequoia semper- 

 virens), and western white pine {Pinus monticola). The highest ocean- 

 ward elevations of the Coast Range are similar to other subalpine 

 areas in the coniferous forests, and are characterized by an open stand 

 of symmetrical conifers, branching to the ground. 



Alpine Summits. — The principal alpine summits are those of the 

 Cascade, Sierra Nevada, and Rocky Mountains, although small 

 areas occur elsewhere. Their vegetation is composed of such dwarfed 

 or prostrate trees as may be able to exist above timber-line, together 

 with low, matted, or polsterform perennial plants with large roots. 

 Meadows or the margins of lakes above timber-line are the habitats of 



