Northwestern forested mountains [Chapter 8]

Product Type: Report, Pages In

Year: 2011

Author(s): Bowman, W.D., J.S. Baron, L. Geiser, M.E. Fenn, and E.A. Lilleskov

Suggested Citation:
Bowman, W.D., J.S. Baron, L. Geiser, M.E. Fenn, and E.A. Lilleskov. 2011. Northwestern forested mountains [Chapter 8]. In: L.H. Pardo, M.J. Robin-Abbott, and C.T. Driscoll (eds.). Assessment of N deposition effects and empirical critical loads of N for ecoregions of the United States. General Technical Report NRS-80. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 75-88 p.

Abstract

8.1 Ecoregion Description

The Northwestern Forested Mountains are ecologically diverse and geographically widespread, encompassing the mountain ecosystems of central and northwestern North America (CEC 1997; Figure 2.2). The ecoregion description is adapted from CEC (1997). Geographically, they extend from the Rocky Mountains and the Sierra Nevada north through the Siskiyous, the east side of the Cascade Range, and then east of the Coast Ranges to interior Alaska. Climatically, the region is characterized by a transition from a moist, maritime climate in the northwest, to a continental and drier climate in the Rockies in the southeast. Orographically generated rainfall creates both rain shadows and wet belts, often in close proximity.

The vegetation of the ecoregion is extremely diverse, with distinct community zonation occurring along elevation gradients. Alpine communities at the highest elevations contain various forb, lichen, and shrub associations. Subalpine communities include lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), Pacific silver fir (Abies amabilis), grand fir (Abies grandis), and Engelmann spruce (Picea engelmannii). Mid-elevation forests are characterized by ponderosa pine (Pinus ponderosa), Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), lodgepole pine, and quaking aspen (Populus tremuloides) in the east, and by western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), Douglas-fir (Pseudotsuga menziesii), and western white pine (Pinus monticola) in the west and southwest. White and black spruce (Picea glauca and P. mariana) dominate the Alaskan portion of the ecoregion. Vegetation of the interior valleys in the southern portion of the region includes big sagebrush (Artemisia tridentate), rabbitbrush (Chrysothamnus spp.), and antelope bitterbrush (Purshia tridentate).