Montana Field Guide

This system is similar to Inter-Mountain Basins Big Sagebrush Steppe, but is characterized by lower herbaceous cover, usually less than 25 percent. In Montana, it occurs as a result of historic and current overgrazing practices and can be considered a disclimax expression of sagebrush steppe. It occurs in broad basins between mountain ranges, on plains and on foothills between 670 and 1,066 meters (2,200-3,500 feet). It can occur on all aspects. Soils are usually fine to coarse textured, well-drained and non-saline. In Montana, these shrublands are dominated by Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and, to a lesser extent, basin big sagebrush (Artemisia tridentata ssp. tridentata). On pristine sites, the shrub layer ranges from 1.2-3.6 meters (4-12 feet). Other shrubs may be present on some occurrences, e.g., Rocky Mountain juniper (Juniperus scopulorum), saltbush (Atriplex species), greasewood (Sarcobatus vermiculatus), rubber rabbitbrush (Ericameria nauseosa) or green rabbitbrush (Chrysothamnus viscidiflorus). Perennial herbaceous cover is usually grasses, although this will vary depending on the other species present and influencing disturbance factors.

Shrubland dominated, lowland elevations, plains, alluvial plains, shallow fine to coarse textured soils, xeromorphic shrubs, shrub cover greater than 10%, Artemsisia tridentata ssp. tridentata, Artemsisia tridentata ssp. wyomingensis, herbaceous cover less than 25 percent

In Montana, this system occurs as a result of historic and current overgrazing practices and can be considered a disclimax expression of sagebrush steppe. These shrublands are dominated by big sagebrush (Artemisia tridentata ssp. tridentata) and/or more commonly, Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis). In some occurrences there are scattered Rocky Mountain juniper (Juniperus scopulorum), greasewood (Sarcobatus vermiculatus), and saltbush (Atriplex species). Rubber rabbitbrush (Ericameria nauseosa) and green rabbitbrush (Chrysothamnus viscidiflorus) may codominate in recently burned stands.

By definition, perennial herbs contribute less than 25% of the vegetative cover (NatureServe 2009) and consist mostly of graminoids, which can vary greatly in composition, depending on the surrounding vegetation type. Dominant grasses can be either rhizomatous or bunch grasses. Perennial forb diversity is quite variable depending on site and treatment; with livestock use the number of introduced species can easily exceed eight on a given site. Common graminoid species can include Indian ricegrass (Achnatherum hymenoides), blue grama (Bouteloua gracilis), threadleaf sedge (Carex filifolia), thickspike wheatgrass (Elymus lanceolatus), needle and thread (Hesperostipa comata), basin wildrye (Leymus cinereus), western wheatgrass (Pascopyrum smithii), Sandberg’s bluegrass (Poa secunda), or bluebunch wheatgrass(Pseudoroegneria spicata). Bluebunch wheatgrass- bunchgrass dominated sites are most prevalent in western Montana. Sod-forming species such as thickspike wheatgrass and western wheatgrass are more common in the eastern portion of the state. Common forbs include yarrow (Achillea millefolium), arrowleaf balsamroot (Balsamorhiza sagittata), scarlet globe mallow (Sphaeralcea coccinea), American vetch (Vicia americana), and plains prickly pear (Opuntia polyacantha) on especially xeric sites. Within this system, cheatgrass (Bromus tectorum) or other annual bromes and invasive weeds can be abundant.

The natural fire regime of sagebrush systems maintains a patchy distribution of shrubs, so in disturbance-free areas, steppe systems would be typical.. However, shrubs increase following heavy grazing and/or with fire suppression. Heavy grazing can lead to a decrease in native bunchgrasses and an increase in exotic grasses such as Kentucky bluegrass (Poa pratensis) and other species.

Big sagebrush is easily killed by fire at all intensities, and when exposed to fire, plants do not re-sprout (Wright and others 1979). In southwestern Montana, researchers have found that fire in mountain big sagebrush is stand replacing, killing or removing most of the aboveground vegetation, and that recovery to pre-burn cover (of sagebrush) takes at least 20 years (Wambolt et al. 2001, Lesica et al. 2005). In Montana, Wyoming big sagebrush may require a century or longer to recover from fire (Lesica et al. 2005).

Heavy grazing practices have also led to a decrease in native grasses and an increase in the spread of annual bromes in some areas of Montana. Sites infested with annual bromes are changing the dynamics of this system by increasing fire potential, severity and spread.

Severely burned sites may require replanting with mountain big sagebrush seedlings due to slow recovery time and low rates of natural seedling recruitment. Generally, larger container volume of nursery stock results in higher outplanting success; 10 to 20 cubic inch container stock is recommended.

Wyoming big sagebrushhas been shown to have subspecies and ecotypes that are morphologically and ecologically distinct. Collecting seeds from the appropriate subspecies in the proposed out-planting site is recommended (Mahalovich and McArthur, 2004). The geographic ranges of each subspecies should serve as the geographic boundary for each seed collection zone, with the additional restriction that seeds and plants should not be moved further than 483 kilometers (300 mi) to a target planting site, or outside their native distribution. These seed transfer guidelines are an indication of the habitat requirements of the subspecies.

Polyploidy is also an important factor in adaptation. Polyploidy can influence plant fertility and vigor, and polyploidy patterns are evident at the ecotonal interfaces and within populations. Polyploids are better adapted to extreme ecological environments than diploids (Sanderson et al, 1989; McArthur and Sanderson, 1999). Thus, specific ecotypes or ploidy level of Wyoming big sagebrush may also be useful for selecting seed sources for outplanting, especially on droughty or mineral soils (Mahalovich and McArthur, 2004).