| Code | Description |
| Engelmann spruce | This type is composed of forests in which either Engelmann spruce or subalpine fir is pure or predominant or where a mixture of the two is predominant. Neither western white pine nor mountain hemlock can be present in significant amounts. |
| Bristlecone pine | Bristlecone pine is pure or predominant; there are rarely intimate associates, althouth many species may be loosely allied with it, such as subalpine fir, Engelmann spruce, aspen (scrubby), ponderosa pine, and pinyon pine. More characteristic still is limber pine which occupies similar sites. |
| Interior Douglas Fir | Douglas-fir is pure or predominant or a mixture of Douglas-fir and white fir is predominant. Neither western larch nor western white pine may be present in significant amounts (over 20 percent). The chief associates are white fir, grand fir, western white pine, western larch, ponderosa pine, and lodgepole pine. In all the western interior mountains just above the ponderosa pine zone and below the Engelmann spruce-subalpine fir, lies a belt at middle elevations that is definitely characterized by the presence of Douglas fir. This belt lies at elevations as high as 8,000 to 9,5000 feet in the South. |
| White fir | Often the stands of this type are practically pure over considerable areas, but where a mixture occurs it may consist of Douglas-fir, ponderosa pine, sugar pine, and other firs. |
| Western white pine | Western white pine is the key indicator species and must be present in significant amounts (over 20 percent). The type as thus defined is limited to north Idaho, Montana, and the adjacent parts of British Columbia. Elsewhere stands containing more than 20% of western white pine are local and rare, and are ecologically distinct. They are not recongized in this classification. |
| Blue spruce | Blue spruce is pure or predominant, and few other conifers are intimately associated with it. Douglas-fir and white fir commonly appear on its edges, and it may associate with Engelmann spruce above and with ponderosa pine below. This is the only well-developed coniferous stream-bank type in the western United States. It is a member of the primary succession (hydrosere) and will disappear whenever the site becomes more dry. |
| Aspen | Quaking aspen is pure or predominant. In the West it extends southward through the Cordillera to northern Mexico, being most widely developed at elevations about coincident with the interior Douglas-fir type, having a mean July temperature of about 60 degrees F. |
| Limber pine | Limber pine is pure or predominant, associated loosely with whitebark and bristlecone pines which have similar ecological characteristics, and often temporarily associated with many other conifers which can readily replace it. This peculiar and perhaps doubtfully valid type is widely but irregularly distributed. Its ecological nature is not fully understood. The limber pine is not an aggressive species. It stands competition poorly and owes its existence to an ability to grow where few other trees can exist. |
| Rocky mountain juniper | Rocky Mountain juniper is either pure or predominant. Frequently there are no other arborescent associates. But other junipers and pinyon pines, ponderosa pine, and oaks (arborescent or scrub) are characteristic southward. Its southern limits are not clear, as it merges into the pinyon-juniper type. Its successional position is unknown. |
| Cottonwood-willow | The presence of narrowleaf cottonwood, lanceleaf cottonwood, black cottonwood, any of the deltoid-leaved, flat-petioled cottonwoods closely allied to the eastern cottonwood, together with arborescent or shrubby willows, mark this streambank type. The most typical coniferous associate is blue spruce. This broad type includes the hardwood river bank complex of the interior and semi-arid region of the western United States. |
| Interior Ponderosa Pine | Ponderosa pine is pure or predominant. The type is limited to the region which lies east of the summit of the Sierra Nevada-Cascade Ranges. The type is often nearly pure, especially in Oregon, South Dakota, Arizona, and New Mexico. |
| Western juniper | Western juniper is pure or predominant, and is typically without arborescent associates. Ponderosa pine and Jeffrey pine appear in parts of the type. |
| Pinyon-juniper | This type consists of a characteristic but variable mixture of several closely related species of juniper and pinyon pines. The pinyon-juniper type is a widely distributed climax type found typically, in elevation, immediately below the interior ponderosa pine type and above the sagebrush or grassland formation. In spite of the variety of species of pine and juniper involved, the type is ecologically homogeneous. |
| Arizona cypress | Arizona cypress is pure or predominant. Pure stands are found locally but usually live oaks (see type 241) or junipers are intermingled. |
| Western live oak | Evergreen (live) oaks are pure or predominant in an area east of the Colorado River. The chief species are Arizona white oak, Mexican blue oak, Emory oak, and silverleaf oak. The live oaks grow in the foothills of southern Arizona and New Mexico and form a type which is the counterpart of the pinyon-juniper type farther north. The type occupies a belt tranging from 4,000 to 6,000 feet elevation, marked by relatively mild and humid winters. |
| Mesquite | Mesquite (together with its varieties) or screwbean mesquite is pure or predominant. |
| NOT SPECIFIED | |
