Idaho Batholith Section of South Central Rockies Forests

North America's former western edge; conservation biology versus restoration ecology

The ranges to the west of the Greater Yellowstone portion of the South Central Rockies forest have more maritime influence and have a few maritime species such as grand fir. However, overall these are dry forests with open canopy of Douglas-fir, ponderosa pine in the canyons, and a sagebrush-forest interface at lower elevations. The canyons of the Salmon, Middle Fork Salmon, South Fork Salmon, and Payette are hot and dry, with ponderosa pine, sagebrush, and grasses. The Sawtooth Valley in the Sawtooth National Recreation Area is a high glacial drift-filled valley with wet meadows, grasslands, and ponderosa pine. To the east, the Boulder and Pioneer Mountains in the Challis and Sawtooth National Forests are dry and partly wooded mountains with open Douglas-fir and shrubland vegetation. Open canopies of Douglas-fir at higher elevations, and sagebrush-grass vegetation are characteristic of the barren mountains in the Lost River, Lemhi, and the Beaverhead Mountains, included in parts of the Challis, Salmon, and Targhee National Forests (McGrath et al. 2001).

The westernmost part of the area is made up of the Salmon River Mountains, a 100- by 200-mile granite range. The Blue Mountains are believed to have joined to western North America about 100 million years ago. This was followed by crustal and mantle melting and granite formation. Granite in the southern portions dates to 83 million years ago, and the northern portions date to 70 million years ago. The present-day valley traversed by US 95 and State Route 55 from Boise north to the Salmon River forms the western boundary of the Idaho batholith. This valley follows the Salmon River suture zone, which separates the North American crust to the east from the Blue Mountains, which are a collage of island arc structures. By 51 million years ago, crustal extension produced the Challis volcanic area to the east of the batholith area (Gaschnig et al. 2011). The Salmon River Mountains are unique in that there is not a distinct trend or dominating crest. The easternmost outcrops of the Idaho batholith include the Anaconda and Sapphire blocks. These areas slid off toward the east and consist of batholith, granites, and sediments bulldozed up against their northeast corner (Schmidt and Schmidt 2000).

Mountains of the Montana portion of this ecoregion range from heavily forested to forest grassland mosaic but tend to have a vegetation of subalpine fir, Douglas-fir and ponderosa pine. Prominent ranges in Montana are the Anaconda, Beaverhead, Flint Creek, Garnet, Pioneer, and Sapphire Mountains. The mountains of the Beaverhead National Forest along the southwestern Montana border with Idaho are dry and open canopy to grassland-dominated with limited forest areas (Woods et al. 1999).

In this ecoregion, fire management is a critical land management issue. Following the big burn of 1910 in northern Idaho and northwestern Montana, most forests were subsequently managed for fire suppression.  Fuels accumulated, many forests are now perhaps more vulnerable to wildfire than at any time in the past, and wildfires are increasing in frequency and extent. Going forward, to make the transition to more natural fire regimes, which potentially involves forest management and occasional fires, there is a potential tension with watershed disruption. On the one hand, forest management and fire contributes nutrients, wood, and habitat diversity to streams. On the other hand, these disruptions can be detrimental in the short term to water quality and watershed processes, thus harming rare aquatic species. Rieman et al. (2010) describe this as a tension between conservation biology and restoration ecology. Maintenance of ecological processes is needed in some areas, restoration of more natural systems is needed in others, and control to maintain systems in a particular state is needed in still others. Across larger landscapes, there should be room for all three approaches. One such area is the South Fork Boise River basin, in the Boise and Sawtooth National Forests. The South Fork Boise watershed includes a variety of forest types and habitats for native salmonid fishes, along with a range of landscapes from pristine to highly altered.  There was no fire in this area for most of the 20^th century. Dry and highly altered forests coincide with high road density, and these areas are where watersheds are most highly altered. The focus in these areas can be the restoration of fire regimes through continued or increased management. Where forest landscapes are in good condition, road density is also low and aquatic habitats also tend to be in good condition. Management can focus on wildland fire use and maintenance of aquatic ecological processes (Rieman et al. 2010).  

There is one National Historic Landmark in the Idaho Batholith section of the South Central Rockies forests. Lemhi Pass (site 1), Beaverhead National Forest, Montana, and Salmon National Forest, Idaho (N44˚38’ W113˚27’), is the site where, on August 12, 1805, a party of the Lewis and Clark expedition led by Meriwether Lewis stood at the pass, the western boundary of Louisiana, and looked over Spanish territory. It remained the western boundary of the US until 1846. Lewis and his party were the first Americans to cross the Continental Divide. It was near here that the expedition also met up with a band of Shoshoni. By extraordinary luck, the Shoshoni chief was Sacajawea’s brother, who was able to offer supplies and horses. The grade to the pass on the eastern Montana side is gentle, and the elevation is 7,373 feet, making it an obvious lower elevation choice to cross the divide. However, the Salmon River Mountains block the way to the west, making the historic trail off the beaten path of modern transportation. Today the site is 12 miles east of Tendoy, Idaho. The pass is a site on the Lewis and Clark National Historic Trail and is crossed by the Continental Divide National Scenic Trail.

References

Gaschnig, Richard M., Jeffrey D. Vervoort, Reed S. Lewis, and Basil Tikoff.  2011.  Isotopic Evolution of the Idaho Batholith and Challis Intrusive Province, Northern U.S. Cordillera.  Journal of Petrology 52:2397-2429.

McGrath, C.L., A.J. Woods, J.M. Omernik, S.A. Bryce, M. Edmondson, J.A. Nesser, J. Shelden, R.C. Crawford, J.A. Comstock, and M.D. Plocher.  2001.  Ecoregions of Idaho (color poster with map, descriptive text, summary tables, and photographs).  Reston, Virginia, U.S. Geological Survey (map scale 1:1,350,000).

Rieman, Bruce E., Paul F. Hessburg, Charles Luce, and Matthew R. Dare.  2010.  Wildfire and Management of Forests and Native Fishes:  Conflict or Opportunity for Convergent Solutions?  BioScience 60:460-468.

Schmidt, Jeremy and Thomas Schmidt. 2000. Guide to America’s Outdoors:  Northern Rockies. National Geographic Society, Washington, DC.

Woods, Alan J., James M. Omernik, John A. Nesser, J. Shelden, and Sandra H. Azevedo.  1999.  Ecoregions of Montana (color poster with map, descriptive text, summary tables, and photographs).  Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000).