Montana Field Guide

This xeric shrubland group is widespread and sometimes a landscape dominant east of the Continental Divide. It is primarily dominated by Wyoming Big Sagebrush communities, though it also includes more localized communities dominated by Basin Big Sagebrush in southwest Montana and by small patches of Threetip Sagebrush or Antelope Bitterbrush. Shrub cover is sparse to dense and consists of shrubs typically 1-3ft. tall, though heights may be up to twice that in the case of Basin Big Sagebrush.
Other shrub species are occasionally present. Perennial, herbaceous species typically contribute greater than 25% vegetative cover and often consists of both rhizomatous and bunchforming graminoids, with a diversity of perennial forbs. These habitats typically occur in broad basins between mountain ranges, and on plains and in the foothills. Typical elevations are from 3,000-5,000ft for Wyoming Big Sagebrush communities though the group extends to elevations of approx 7,000ft for communities dominated by Antelope Bitterbrush, Basin Big Sagebrush and Threetip Sagebrush. The group occurs as an extensive matrix on level to gently rolling plains, on toeslopes and in valley bottoms, as well as in small and large patches in dissected landscapes such as breaks and badlands. It can occur on all aspects. Soils are shallow, fine to coarse textured, well drained and mostly non-saline.

Some communities in this group provide important wildlife habitat for species such as Sage Grouse and Pronghorn as well as many other animal and plant species.

This Group encompasses the Big Sagebrush Steppe and the Big Sagebrush Shrubland Ecological Systems.

Semi-Arid Shrubland and Steppe; Intermountain and Great Plains Regions; Valleys, Plains, Foothills; Xeromorphic Shrubs, Shrub Cover >10%

Typical Dominants: Basin Big Sagebrush (Artemisia tridentata ssp. tridentata), Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis), Threetip Sagebrush (Artemisia tripartita), Antelope Bitterbrush (Purshia tridentata)

This Group occurs primarily east of the Continental Divide in the Intermountain Valleys, Bighorn Basin and in the Great Plains. In the lower elevation valleys of southwest Montana, Wyoming Big Sagebrush is a common community. Basin Big Sagebrush communities are restricted mainly to stream terraces in Beaverhead County. On the Great Plains and in the foothills, Wyoming Big Sagebrush Steppe can be found in localized patches to widespread areas on the landscape where it has not been eradicated by agricultural practices or fire. In southwest Montana, including in areas west of the Continental Divide such as the Foothills surrounding the Bitterroot Valley, this Group is represented by small patches of Antelope Bitterbrush. Threetip Sagebrush communities are confined primarily to Beaverhead County.

In Montana, G302 occurs in Level III Ecoregions: 16 (Idaho Batholith), 17 (Middle Rockies), 18 (Wyoming Basin), 42 (Northwestern Glaciated Plains) and 43 (Northwestern Great Plains).

In Montana, G302 occurs or potentially occurs within these Major Land Resource Areas: 43B - Central Rocky Mountains, 44A - Northern Rocky Mountain Valleys, 44B - Central Rocky Mountain Valleys, 46 Northern and Central Rocky Mountain Foothills, 52 - Brown Glaciated Plains; 53A - Northern Dark Brown Glaciated Plains, 58A,B,C,D - Northern Rolling High Plains, 60A,B - Pierre Shale Plains.

Matrix

This group occurs throughout much of the western U.S., typically in broad basins between mountain ranges, and on plains and in the foothills. Typical elevations are from 3,000-5,000ft for Wyoming Big Sagebrush communities though the group extends to elevations of approx 7,000ft for communities dominated by Antelope Bitterbrush, Basin Big Sagebrush and Threetip Sagebrush. The group occurs as an extensive matrix on level to gently rolling plains, on toeslopes and in valley bottoms, as well as in small and large patches in dissected landscapes such as breaks and badlands. It can occur on all aspects. Soils are shallow, fine to coarse textured, well drained and mostly non-saline. They developed from various parent materials that have weathered to predominantly heavy-textured, clay-rich Aridisols, and in more mesic conditions, Mollisols. In southeastern Montana, these sites are associated with heavy soils developed from shales and mudstones. In north-central Montana, soils tend to be shallower, often with gravelly or claypan surfaces.

In Montana, these communities are dominated by Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis), Basin Big Sagebrush (Artemisia tridentata ssp. tridentata) or occasionally by Threetip Sage (Artemisia tripartita), or Antelope Bitterbrush (Purshia tridentata). Other shrubs may be present, including Silver Sagebrush (Artemisia cana), Black Greasewood (Sarcobatus vermiculatus), Shadscale (Atriplex species), Rubber Rabbitbrush (Ericameria nauseosa), and Green Rabbitbrush (Chrysothamnus viscidiflorus) depending on specific site characteristics. Shrub cover can vary significantly and stands may be open to dense. Shrub heights are typically 1-3ft., though heights may be up to twice that in the case of Basin Big Sagebrush.

Perennial herbaceous components typically contribute greater than 25% vegetative cover and consists of rhizomatous and bunchforming graminoids, with a diversity of perennial forbs. In Montana, the dominant graminoids include Western Wheatgrass (Elymus smithii), Bluebunch Wheatgrass (Elymus spicatus), Indian Ricegrass (Oryzopsis hymenoides), Needle-and-Thread (Stipa comata), blue grama (Bouteloua gracilis), Sandberg’s Bluegrass (Poa secunda). Dryland rhizomatous sedges such as threadleaf sedge (Carex filifolia) and needleleaf sedge (Carex duriuscula) are common at some sites.

Common forbs include Hood’s phlox (Phlox hoodii), sandwort (Arenaria species), prickly pear (Opuntia species), scarlet globemallow (Sphaeralcea coccinea), purple prairie clover (Dalea purpurea), gayfeather (Liatris punctata), and milkvetch (Astragalus species). Within this system, cheatgrass (Bromus tectorum), Japanese brome (Bromus japonicus) and other invasive weeds can be abundant where there is frequent disturbance.

In Montana, this group encompasses 21 Associations grouped into 5 Alliances within the National Vegetation Classification. These likely cover the range of variation within vegetation communities in Wyoming Big Sagebrush dominated communities in the state.

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.

Some communities in this group provide important wildlife habitat for species such as Sage Grouse and Pronghorn as well as many other animal and plant species. In the absence of natural fire, periodic prescribed burns can be used to maintain and restore this system to similar pre-settlement conditions. Low intensity prescribed fire is used to reduce sagebrush cover, to increase herbaceous forage and to improve habitat quality for sage grouse and other wildlife by creating a mosaic of burned and unburned patches. Researchers in southwestern Montana found that prescribed fire resulted in an average increase of 13% in grass canopy cover; followed by light grazing, fire may be a way of rejuvenating mountain big sagebrush stands. Furthermore, prescribed fire or wildfire generally causes only a small increase in the cover of forbs overall, and will have no effect on the abundance of plants in the Cichorieae tribe of the Asteraceae, an important food source for rearing sage grouse broods (Lesica et al 2005). Excessive grazing can result in the loss of the most common perennial grasses in this system and promote the spread of cheatgrass.

In the absence of natural fire, periodic low intensity prescribed burns can be used to maintain and restore this system to similar pre-settlement conditions. Low intensity prescribed fire is used to reduce sagebrush cover; in order to increase herbaceous forage and improve habitat quality for sage grouse and other wildlife by creating a mosaic of burned and unburned patches. Excessive grazing can result in the demise of the most common perennial grasses in this system and lead to an abundance of Cheatgrass or Japanese Brome.

Severely burned sites may require replanting with Wyoming 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 sagebrush has 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.

Successful restoration of native grasses within this system may be limited to sites where pre-fire cheatgrass cover was low. Fall germination and rapid elongation of roots provide cheatgrass with a competitive advantage over native perennial species (Harris 1967). In trials, cheatgrass reduced growth of bluebunch wheatgrass seedlings and was capable of producing twice the root quantity of bluebunch wheatgrass during the first 45 days of growth (Aguirre and Johnson, 1991). Prolific seed production also contributes to the competitive advantage of this species over native grasses. However, some selections of bluebunch wheatgrass exhibit desirable growth characteristics that hold promise for establishing this species on cheatgrass-infested sites.

M.E. Hall and K.A. Schulz 2015

S. Mincemoyer, L. Vance, T. Luna, S.V. Cooper

12/5/2024