This system dominates the montane and subalpine landscape of southwestern Montana from valley bottoms to subalpine ridges and is found as far north as Glacier National Park. It can also be seen in the island mountain ranges of the north-central and south-central portions of the state. 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. The shrub component of this system is generally dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana). Other co-dominant shrubs include silver sagebrush (Artemisia cana ssp. viscidula), subalpine big sagebrush (Artemisia tridentata ssp. spiciformis), three tip sagebrush (Artemisia tripartita ssp. tripartita) and antelope bitterbrush (Purshia tridentata). Little sagebrush (Artemisia arbuscula ssp. arbuscula) shrublands are only found in southwestern Montana on sites with a perched water table. Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) sites may be included within this system if occurrences are at montane elevations, and are associated with montane graminoids such as Idaho fescue (Festuca idahoensis), spike fescue (Leucopoa kingii), or poverty oatgrass (Danthonia intermedia). In ares where sage 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). Because of the mesic site conditions, most occurrences support a diverse herbaceous undergrowth of grasses and forbs. Shrub canopy cover is extremely variable, ranging from 10 percent to as high as 40 or 50 percent.
Montane to subalpine zone, deep, aridic soils, xeromorphic shrubs, bunchgrasses, shrub cover greater than 10%, Artemsisia tridentata ssp. vaseyana
This ecological system occurs at montane to subalpine zones. In southwestern Montana, this system is found from 1,844 meters to 3,200 meters (6,050-10,500 feet) (Lesica et al, 2005). Much of the precipitation occurs as snow at a range of 40.3 cm (15 in.) in valley locations to upwards of 74.3 cm (35 in) along the mountain crests. Temperatures are continental with large annual and diurnal variations. In general, this system shows an affinity for mild topography, fine soils, and some source of subsurface moisture. 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 system primarily occurs on deep-soiled to stony flats, ridges, nearly flat ridgetops, and mountain slopes, but at high elevation, may be restricted to south- or west-facing slopes. In Wyoming and Montana, three tip sagebrush (Artemisia tripartita ssp. tripartita) associations are part of this system, occurring at higher elevations than the similar Inter-Mountain Basins Big Sagebrush Steppe ecological system.
In Montana, most of this system is dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana). Mountain big sagebrush occurs in all regions, although tends to be found only on on the highest mesas. Silver sagebrush (Artemisia cana ssp. viscidula) and subalpine big sagebrush (Artemisia tridentata ssp. spiciformis) can be co-dominant on some sites. Three tip sagebrush is found only in southwestern and west-central Montana where it functions primarily as a seral component, increasing in frequency following fire. Antelope bitterbrush (Purshia tridentata) may codominate, but as a codominant is of very limited occurrence, being found primarily on intrusive volcanics in western and west-central Montana. Both subspecies of little sagebrush (Artemisia arbuscula ssp. arbuscula, and A. arbuscula ssp. longiloba) dominated shrublands occur sporadically within this system in southwestern Montana, which is the most northerly extent of their distribution. Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) dominated sites may be included in this system if they occur in the montane zone, which is most reliably indicated by the presence of Idaho fescue (F. idahoensis). These relatively uncommon sites occur above 1,280 m (4,200 feet) on the mesas of eastern Montana and the dry valleys of southwestern Montana.
Other shrubs may be present, but usually at low cover values (5-10%). Species inlcude rubber rabbitbrush (Ericameria nauseosa), and green rabbitbrush (Chrysothamnus viscidiflorus), wax currant (Ribes cereum), Woods rose (Rosa woodsii), deerbrush ceanothus (Ceanothus velutinus), snowberry (Symphoricarpos species) and serviceberry (Amelanchier alnifolia). In ares where sage has been eliminated by human activities like burning, disking or poisoning, these other shrubs may dominate the steppe system. This can be seen around Garrison and Deer Lodge, where the sage steppe ecological system contains only minimal amounts of sage.
The herbaceous layer is usually well represented. Graminoids that can be abundant include rough fescue (Festuca campestris), Idaho fescue (Festuca idahoensis), bottlebrush squirreltail (Elymus elymoides), pinegrass (Calamagrostis rubescens), needlegrass (Achnatherum species), spike fescue (Leucopoa kingii), poverty otagrass (Danthonia intermedia), western wheatgrass (Pascopyrum smithii), mountain brome (Bromus carinatus), slender wheatgrass (Elymus trachycaulus), prairie junegrass(Koeleria macrantha), bluebunch wheatgrass (Pseudoroegneria spicata), Sandberg’s bluegrass (Poa secunda), and are variety of dry, upland sedges such as threadleaf sedge (Carex filifolia) and Geyer’s sedge (Carex geyeri) (Mueggler and Stewart, 1988).
Forb diversity is frequently is moderate to high, commonly exceeding 30 species in a 400 m2 macroplot. Species may include arrowleaf balsamroot (Balsamorhiza sagittata), Indian paintbrush (Castilleja species), cinquefoil (Potentillaspecies), fleabane (Erigeron species), phlox (Phlox species), milkvetch (Astragalus species), prairie smoke (Geum triflorum), lupine (Lupinus species), buckwheat (Eriogonum species), yarrow (Achillea millefolium), rosy pussytoes (Antennaria rosea), wild strawberry (Fragaria virginiana), and western sagewort (Artemisia ludoviciana). Missouri pricklypear (Opuntia polycantha) is common on sites in southwestern Montana (Cooper et al, 1999).
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). 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 sagebrushcover 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, so 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 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).
Severely burned sites may require replanting with mountain big sagebrush seedlings due to the slow recovery time within this system 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 sagebrushhas been shown to be made 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.
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 big sagebrush may also be useful for selecting seed sources for outplanting on droughty or mineral soils (Mahalovich and McArthur, 2004).
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