Montana Field Guide

This shrub and shrub-steppe group dominates the non-forested, montane and subalpine landscape of southwestern Montana from valley bottoms to subalpine ridges. It is found as far north as Glacier National Park and can also be seen in the island mountain ranges of the north-central and south-central portions of the state. The shrub component of this system is dominated by Mountain Big Sagebrush (Artemisia tridentata ssp. vaseyana). Rarely are sites dominated by Subalpine Big Sagebrush (Artemisia spiciformis, Artemisia tridentata ssp. spiciformis) in extreme southern Montana. Other co-dominant shrubs include Silver Sagebrush (Artemisia cana ssp. viscidula) and Mountain Snowberry (Symphoricarpos oreophilus). It primarily occurs on deep-soiled to stony flats, ridges, nearly flat ridgetops, and mountain slopes. In general, this system occurs in areas of gentle topography, fine soils, subsurface moisture or mesic conditions, within zones of higher precipitation and areas of snow accumulation. It occurs on all slopes and aspects, variable substrates and all soil types. Low Sagebrush (Artemisia arbuscula) shrublands may be found on adjacent sites in southwestern Montana on less productive, shallower, rockier soils. Graminoids and forbs are often common at these sites. In areas where sagebrush has been eliminated by human activities like burning, disking or poisoning, other shrubs may be dominant, especially rubber rabbitbrush (Ericameria nauseosa), and Green Rabbitbrush (Chrysothamnus viscidiflorus). Shrub canopy cover is extremely variable, ranging from 10 percent to as high as 50 percent at some sites.

This Group is largely equivalent to the Montane Sagebrush Steppe Ecological System.

Montane and subalpine zones; Shrubland and Steppe; Rocky Mountain Region; Xeromorphic Shrubs; Shrub Cover >10%; Bunchgrasses; Deep, Aridic Soils.

Typical Dominants: Mountain Big Sagebrush (Artemisia tridentata ssp. vaseyana), Snowfield or Spiked Big Sagebrush (Artemisia spiciformis)

In Montana, this type is a landscape dominant of southwestern Montana from the higher valleys to subalpine ridges and is found as far north as Glacier National Park in western Montana. Mountain Big Sagebrush Shrublands also occur in the island mountain ranges of central and southern MT.

In MT, G304 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies) and 41 (Canadian Rockies)

In Montana, G304 occurs within these Major Land Resource Areas: 43A - Northern Rocky Mountains, 43B - Central Rocky Mountains, 44B - Central Rocky Mountain Valleys, and 46 - Northern and Central Rocky Mountain Foothills

Large Patch

This type occurs primarily in the montane and subalpine zones. In southwestern Montana, it is found from 6,000-10,500 feet (Lesica et al 2005). In northwestern MT, it occurs down to 3,000 feet while in central Montana it is mostly found between 4,000 and 6,500 feet. Precipitation ranges from 15 inches in valley locations to upwards of 35 inches along the mountain crests. Snowfall accounts for substantial portions of the annual precipitation. Temperatures are continental with large annual and diurnal variations. In general, this system shows an affinity for gentle topography. Soils are generally moderately deep to deep, well-drained, and loam, sandy loam, clay loam, or gravelly loam textural classes. Soils often have a substantial volume of coarse fragments, and are derived from a variety of parent materials. This type primarily occurs on deep-soiled to stony flats, ridges, nearly flat ridgetops, and mountain slopes, but at high elevation, is typically restricted to south- or west-facing slopes.

In Montana, this community is dominated by and/or defined by Mountain Big Sagebrush (Artemisia tridentata ssp. vaseyana) which forms stands that are generally 0.5-1 meter in height. Silver Sagebrush (Artemisia cana ssp. viscidula) and/or Subalpine Big Sagebrush (Artemisia spiciformis or A. tridentata ssp. spiciformis) are rarely co-dominant on some sites. Other shrubs may be present, but usually have low cover (5-10%). Species include Rubber Rabbitbrush (Ericameria nauseosa), and Green Rabbitbrush (Chrysothamnus viscidiflorus), Mountain Snowberry (Symphoricarpos oreophilus), Wax Currant (Ribes cereum), and Woods’ Rose (Rosa woodsii). Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) generally occurs at elevations below Mountain sagebrush in areas where they co-occur.

The herbaceous layer is usually well represented to abundant with cover generally over 25%. Common graminoids include Rough Fescue (Festuca campestris), Idaho Fescue (Festuca idahoensis), Bluebunch Wheatgrass (Elymus spicatus), Slender Wheatgrass (Elymus trachycaulus), Mountain Brome (Bromus carinatus), Prairie Junegrass (Koeleria macrantha), Sandberg’s Bluegrass (Poa secunda), Bottlebrush Squirreltail (Elymus elymoides), Nelson's Needlegrass (Stipa nelsonii), Spike Fescue (Leucopoa kingii), and Timber Oatgrass (Danthonia intermedia). A variety of dry, upland sedges such as Threadleaf Sedge (Carex filifolia) and Geyer’s Sedge (Carex geyeri) are often present (Mueggler and Stewart 1988).

Forb diversity is often moderate to high, commonly exceeding 30 species in a 400 m2 macroplot. Species may include Arrowleaf Balsamroot (Balsamorhiza sagittata), Indian Paintbrush (Castilleja species), Sandwort (Arenaria congesta), Cinquefoil (Potentilla species), Fleabane (Erigeron species), Phlox (Phlox species), Milkvetch (Astragalus species), Prairie Smoke (Geum triflorum), Lupine (Lupinus species), Buckwheat (Eriogonum species), Common Yarrow (Achillea millefolium), Rosy Pussytoes (Antennaria rosea), Wild Strawberry (Fragaria virginiana), and Western Sagewort (Artemisia ludoviciana). Plains Pricklypear (Opuntia polyacantha) is common on sites in southwestern Montana (Cooper et al 1999). Weeds, particularly Cheatgrass may be abundant as some sites. Mosses and lichens may be common on some sites with the mosses usually confined to areas underneath the shrub canopy. Lichens may occur on the soil surface, on rocks or on woody debris.

In Montana, this group is represented by 9 Associations grouped into 3 Alliances within the National Vegetation Classification, which likely covers the range of types within the state in Mountain Big Sagebrush communities.

The natural fire regime has been greatly altered within these communities, and therefore shrub cover can be highly variable. Big sagebrush is easily killed by fire at all intensities, and when exposed to fire, plants do not re-sprout (Wright et al, 1979). In southwestern Montana, Wambolt etal (2001) and Lesica etal (2005) have also shown that fire in big sagebrush is stand-replacing, killing or removing most of the above-ground vegetation, and that recovery to pre-burn cover (of sagebrush) may require 15 or more years for basin big sagebrush, and on average approximately 32 years for mountain big sagebrush (Lesica et al 2005, Cooper et al. 2007).

Fire and grazing can alter this system but can also be used for management. Overgrazing reduces native bunchgrasses and often allows an increase in exotic grasses such as Kentucky bluegrass (Poa pratensis) or Cheatgrass. However, managed grazing can be used to reduce unnaturally high fuel loads. In the absence of natural fire, periodic prescribed burns can be used to maintain and restore sagebrush steppe to pre-settlement conditions. Low intensity prescribed fire is used to reduce sagebrush cover and to increase herbaceous forage and improve habitat quality for sage grouse and other wildlife by creating a mosaic of burned and unburned patches. Results in southwestern Montana indicate that prescribed fire resulted in an average increase of 13% in grass canopy cover, followed by light grazing, this may be a way of rejuvenating mountain big sagebrush stands. Prescribed fire or wildfire will induce only a small increase in the cover of forbs 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). In areas where sage has been eliminated by human activities like burning, disking or poisoning, other shrubs may dominate the steppe system. This can be seen around Garrison and Deer Lodge, where the sage steppe communities contain only minimal amounts of sage.

Severely burned sites may require replanting with mountain big sagebrush seedlings due to the 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 for use on these sites.

Big sagebrush has been shown to consist of 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 native distribution of each subspecies serves as the geographic boundary for each seed collection zone, with the additional restriction that seeds and plants should not be moved further than 483 km (300 mi) to their target planting site. These seed transfer guidelines are an indication of the habitat requirements of the subspecies.

The presence of polyploidy in some plant species is also an important factor to consider in local adaptation. Polyploidy can influence plant fertility and vigor and polyploids are often better adapted to extreme ecological environments than diploids (Sanderson et al 1989; McArthur and Sanderson 1999). Thus, specific ecotypes or ploidy level of big sagebrush may also be useful for selecting seed sources for outplanting on droughty or mineral soils (Mahalovich and McArthur 2004).

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

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

12/5/2024