Forest Types and Life Zones (continued)

WESTERN FOREST TYPES

The western forests are predominantly coniferous except at the lowest elevations in the Southwest. There the desert species that attain tree size are mostly spiny deciduous species or giant yuccas and cacti.

Starting at the Mexican border and proceeding northward we encounter the following types:¹

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¹Various representative areas of the National Park System are given in which the types referred to are found. Not all areas of the National Park System where these types occur are mentioned by name.

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The desert vegetative type is found in the Lower Sonoran Life Zone, the lowest and driest regions, in which mesquite, catclaw acacia, paloverde, saguaro, and Joshua-tree attain tree size and creosotebush and desert saltbush are characteristic shrub species. Into this category fall the lowest elevations of Big Bend and Grand Canyon National Parks and of Oregon Pipe Cactus, Saguaro, Joshua Tree, and Death Valley National Monuments. However, not all of the above-named species occur in every one of these areas.

Pinyon-juniper woodland, oak woodland, chaparral, and sagebrush are various types that occur in the Upper Sonoran Life Zone, in which pinyon and several species of juniper and oak are characteristic tree species, and scrub live oak, sagebrush, manzanita, sumac, cliff rose, and ceanothus are representative shrub species. These types occur at the elevations immediately above those of the desert type in the areas listed in the preceding paragraph, and also in Zion National Park. A good illustration of the pinyon-juniper type occurs in Mesa Verde National Park, and of the chaparral type on the lower western slopes of Sequoia National Park.

The Transition Life Zone is the next higher zone, with a greater amount of rainfall. It includes many of the most interesting and varied species and types of our western forests. In this zone are found the giant sequoia groves of the Sierras, with white fir, sugar pine, ponderosa pine, and incense-cedar as associated species; the redwood forests of California and the Olympic rain forest in Washington, both of which occur within the more humid coastal areas of this life zone; and the ponderosa pine forests, which are considered typical of the Transition Life Zone. Ponderosa pine has one of the most extensive ranges of the western conifers.

The ponderosa forest is represented excellently in Grand Canyon National Park, where, on the North Rim especially, it forms a beautiful open stand interspersed with aspen, and with occasional meadows in which large numbers of mule deer may be seen grazing. The white tailed Kaibab squirrel is also a resident of this area. The combination of open forest, into which one can see readily, and abundant animal life makes this one of the most attractive recreational forests of the National Park System.

Ponderosa pine reaches its optimum growth in the Sierra forests of California and, in mixture with sugar pine, white fir, and incense-cedar, is well represented in Sequoia, Kings Canyon, and Yosemite National Parks. It occurs also in Lassen Volcanic National Park and in the southeast portion of Crater Lake National Park.

In the Rocky Mountain region a good sample of the ponderosa pine forest is found in the western part of Glacier National Park. It also occurs on the lower elevations of the east side of Rocky Mountain National Park, but does not extend up into Yellowstone and Grand Teton National Parks. It is somewhat surprising to find a ponderosa pine forest of approximately 8,000 acres on the higher portion of Saguaro National Monument, with some mixture of Douglas-fir and limber pine. Ponderosa pine grows also in Dinosaur National Monument and in Bryce Canyon, Zion, Mesa Verde, Carlsbad Caverns, and Big Bend National Parks.

Douglas-fir forests are typical of the next higher zone, known as the Canadian Life Zone. Douglas-fir reaches its maximum development, both in size and quantity, in the Northwest. The Douglas-fir type species of the Pacific coast forests is distinguishable from that of the Rocky Mountain region, the latter designated as Pseudotsuga taxifolia var. glauca. Douglas-fir forests are prominent in Olympic and Mount Rainier National Parks, and the species occurs to a lesser extent in mixture with Western white pine and red fir in Crater Lake, Lassen Volcanic, and Yosemite National Parks. In the Rocky Mountain region, Douglas-fir extends from Glacier National Park, at the Canadian line, to Big Bend National Park, at the Mexican boundary. In the Rockies it is found in pure stands or mixed with other Rocky Mountain conifers.

Lodgepole pine forests are also prominent in the Canadian Life Zone and extend into the next higher Hudsonian Life Zone. Lodgepole forests are very extensive in Glacier and Yellowstone National Parks. In the latter park they form three-quarters of the forest stand over a vast area. Lodgepole stands are also important in Grand Teton, Rocky Mountain, and Crater Lake National Parks, and, to a lesser extent, in the high country of Lassen Volcanic, Yosemite, and Sequoia National Parks.

A number of other interesting species, such as Jeffrey pine, limber pine, foxtail pine, whitebark pine, blue spruce, Engelmann spruce, mountain hemlock, balsam fir, alpine fir, and white fir are found in various parts of the Canadian Life Zone. Some of these extend up into the Hudsonian Life Zone, and a number extend down into the Transition Life Zone.

Within the western forests of the Transition and Canadian Life Zones, interspersed stands of quaking aspen, with their broader, shimmering leaves of lighter color, add materially to the scenic attractiveness of the coniferous forests. In the autumn, especially in the Rocky Mountain region, the golden aspen, in mixture with the green conifers, creates landscapes of great beauty. In Washington, Oregon, and California, the vivid coloring of the Pacific dogwood adds another attractive element to the scene, as does that of the vine maple.

The spruce-fir forest, in which Engelmann spruce, alpine fir, and white and black spruce are index species, is characteristic of the forest just below timberline, in the Hudsonian Life Zone. This type is found on numerous high mountains in the western national parks. In Mount McKinley National Park, in Alaska, white spruce is the dominant forest species.

Above timberline on the high mountains, dwarf shrubs of willow, birch, and alder are representative woody species in the vegetative cover adapted to the rigorous growing conditions in the Alpine Life Zone. In the arctic region, treeless expanses, or tundra, support a turf of prostrate shrubs of the foregoing species, together with various grasses, sedges, lichens, and moss. Arctic tundra is well represented in Mount McKinley National Park.