Invalid Unit Specified
M169 Artemisia tridentata - Artemisia tripartita ssp. tripartita - Purshia tridentata Steppe & Shrubland Macrogroup

The U.S. National
Vegetation Classification
Type Concept Sentence: This macrogroup includes the big sagebrush shrubland and shrub-steppe that is a matrix and large-patch type throughout much of the intermountain western U.S. and that is dominated by Artemisia tridentata, Purshia tridentata, and several local dominants such as Artemisia cana and Artemisia tripartita ssp. tripartita.
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Common (Translated Scientific) Name: Big Sagebrush - Threetip Sagebrush - Antelope Bitterbrush Steppe & Shrubland Macrogroup
Colloquial Name: Great Basin-Intermountain Tall Sagebrush Steppe & Shrubland
Hierarchy Level: Macrogroup
Type Concept: This sagebrush shrubland and shrub-steppe macrogroup is widely distributed in the western U.S. It has an open to dense (10-80% cover) short-shrub canopy (<2 m tall) dominated by Artemisia tridentata. Purshia tridentata is less widespread but often dominates or codominates with Artemisia tridentata, especially in relatively mesic and montane stands. The subspecies of Artemisia tridentata vary by habitat and geographic range. The most widespread taxa are Artemisia tridentata ssp. wyomingensis and Artemisia tridentata ssp. tridentata. Some stands are codominated by associated shrub species Atriplex canescens, Atriplex confertifolia, Ephedra nevadensis, Ephedra viridis, Ericameria nauseosa, Grayia spinosa, Sarcobatus vermiculatus, or Tetradymia canescens. Artemisia tridentata ssp. tridentata, Artemisia tridentata ssp. xericensis, and Artemisia tripartita ssp. tripartita are characteristic of relatively mesic environments. Mesic associates include Peraphyllum ramosissimum, Prunus virginiana, and Symphoricarpos spp. At montane elevations, Artemisia tridentata ssp. vaseyana, Artemisia cana, and related taxa such as Artemisia tridentata ssp. spiciformis dominate, sometimes with Purshia tridentata codominating or dominating stands. Amelanchier utahensis and Symphoricarpos oreophilus are common montane associates. The understory of this macrogroup is variable and characterized by a sparse to dense (5-50% cover) herbaceous layer that is dominated by a variety of perennial graminoid associates. On xeric sites Achnatherum hymenoides, Hesperostipa comata, Poa secunda, and other semi-desert associates are common. On relatively mesic or montane sites, associates include Achnatherum occidentale, Bromus carinatus, Calamagrostis rubescens, Carex pensylvanica, Danthonia intermedia, Deschampsia cespitosa, Elymus trachycaulus, Festuca arizonica, Festuca idahoensis, Leucopoa kingii, Leymus cinereus, Poa fendleriana, and Pseudoroegneria spicata. Shrub-steppes characterized by an open shrub canopy and abundant native graminoid understory are more common in the less xeric northern extent, at montane elevations and mesic microsites such as along drainages. Shrublands are more common in the drier southern extent with the core distribution in the Great Basin and Colorado Plateau. Stands are found as low as 500 m elevation in the northwestern Great Plains and up to 2500 m in the Rocky Mountains and Colorado Plateau. Xeric stands occur on flat to steeply sloping upland slopes on alluvial fans and terraces, toeslopes, lower and middle slopes, draws, badlands, foothills, and rocky slopes. Mesic stands occur on stream terraces, point bars, valley floors, alluvial fans, floodplains, washes, gullies, stabilized dunes, mesic uplands, and swales. Montane stands occur on stony flats, broad ridgetops, and mountain slopes. All aspects are represented, but occurrences at higher elevations may be restricted to south- or west-facing slopes. Soils vary from deep and well-developed to shallow rocky and poorly developed substrates.
Diagnostic Characteristics: This sagebrush shrubland and shrub-steppe macrogroup has an open to dense (10-80% cover) short-shrub canopy (<2 m tall) dominated by strong diagnostic species Artemisia tridentata. Purshia tridentata is a less widespread diagnostic species that often dominates or codominates with Artemisia tridentata or other shrubs. Artemisia tridentata subspecies vary by habitat and geographic range and are valuable as diagnostic taxa for classification. The most widespread diagnostic taxa are Artemisia tridentata ssp. wyomingensis and Artemisia tridentata ssp. tridentata. Stands may be codominated by associated shrub species Amelanchier utahensis, Atriplex canescens, Ephedra nevadensis, Ephedra viridis, Ericameria nauseosa, or Sarcobatus vermiculatus. Relatively mesic environments are characterized by large Artemisia tridentata ssp. tridentata, Artemisia tridentata ssp. xericensis, and Artemisia tripartita ssp. tripartita. At montane elevations Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. spiciformis, and Artemisia cana ssp. viscidula are the dominant diagnostic taxa. The understory is variable (5-50%) and dominated by a variety of perennial graminoid associates. Shrub-steppe with abundant native graminoid understory is more common in the less xeric northern extent and at montane elevations, as well as mesic microsites such as along drainages.
Rationale for Nominal Species or Physiognomic Features: The nominal species Artemisia tridentata, Artemisia tripartita ssp. tripartita, and Purshia tridentata are the most common and widespread dominant and diagnostic species of this shrubland and shrub-steppe macrogroup and Artemisia cana and Artemisia rothrockii are minor diagnostic species.
Classification Comments: This wide-ranging and broadly defined macrogroup is characterized by Artemisia tridentata and several other less common sagebrushes, such as Artemisia cana, Artemisia rothrockii, Artemisia tripartita ssp. tripartita, and Purshia tridentata. S.K. Rust and other ecologists think Intermountain Mountain Big Sagebrush Steppe & Shrubland Group (G304) should be moved out of this macrogroup and into Central Rocky Mountain Montane-Foothill Grassland & Shrubland Macrogroup (M048) or Southern Rocky Mountain Montane Shrubland Macrogroup (M049) because of the strong associations with Artemisia tridentata ssp. vaseyana and relatively mesic montane environment versus the warmer, drier environment characterized by the occurrence of Artemisia tridentata ssp. wyomingensis and Artemisia tridentata ssp. tridentata that occurs on the lower-elevation plateaus and planes of the Columbia Basin and Great Basin (S.K. Rust personal comm. 2014). Until further review, G304 will stay in this macrogroup.
Similar NVC Types:
M170 Great Basin-Intermountain Dwarf Sagebrush Steppe & Shrubland, note: is dominated by dwarf-shrubs.
Physiognomy and Structure: This microphyllous-leaved evergreen and broad-leaved, cold-deciduous macrogroup is structurally characterized by open to dense sagebrush with associated shrubs interspersed. A sparse to dense perennial herbaceous understory dominated by bunchgrasses is common. Scattered forbs may be present, but typically are not.
Floristics: This sagebrush shrubland and shrub-steppe macrogroup is characterized by an open to dense (10-80% cover) short-shrub canopy (<2 m tall) that is dominated by Artemisia tridentata. Purshia tridentata frequently dominates or codominates with Artemisia tridentata. The subspecies of Artemisia tridentata have diagnostic value for community classification and vary by habitat and geographic range. Artemisia tridentata ssp. wyomingensis and Artemisia tridentata ssp. tridentata are the most widespread taxa and dominate throughout much of range of this macrogroup. They may be codominated by associated shrub species such as Atriplex canescens, Chrysothamnus viscidiflorus, Ephedra nevadensis, Ephedra viridis, Ericameria nauseosa, or Sarcobatus vermiculatus. Artemisia tridentata ssp. tridentata, Artemisia tridentata ssp. xericensis, and Artemisia tripartita ssp. tripartita are characteristic of relatively mesic environments and may be codominated by Peraphyllum ramosissimum, Prunus virginiana, Ribes cereum, or Symphoricarpos spp. At montane elevations, Artemisia tridentata ssp. vaseyana, related taxa Artemisia tridentata ssp. spiciformis, and Artemisia cana ssp. viscidula are the dominant taxa. Purshia tridentata may also dominate or codominate montane stands. Common montane associates are Amelanchier utahensis and Symphoricarpos oreophilus. The understory is variable (5-50% cover) and dominated by a variety of perennial graminoid associates. On xeric sites Achnatherum hymenoides, Hesperostipa comata, Poa secunda, and other semi-desert associates are common. Montane and relatively mesic sites include Achnatherum occidentale, Bromus carinatus, Calamagrostis rubescens, Carex pensylvanica, Danthonia intermedia, Deschampsia cespitosa, Elymus trachycaulus, Festuca arizonica, Festuca campestris, Festuca idahoensis, Leucopoa kingii, Leymus cinereus, Poa fendleriana, and Pseudoroegneria spicata. Shrub-steppe with abundant native graminoid understory is more common in the less xeric northern extent and at montane elevations, as well as mesic microsites such as along drainages. Shrublands are more common in the drier southern extent with the core distribution in the Great Basin and Colorado Plateau.
Dynamics: The natural fire regime of this macrogroup likely maintains a patchy distribution of shrubs so that the general aspect of the vegetation is a grassland. Shrubs may increase following heavy grazing and/or with fire suppression, particularly in moist portions in the northern Columbia Plateau where it forms a landscape mosaic pattern with shallow-soil scabland shrublands. Response to grazing can be variable depending on the type of grazer and the season in which grazing occurs. Hesperostipa comata can increase in abundance in response to either grazing or fire. In central and eastern Montana (and possibly elsewhere), complexes of prairie dog towns are common in instances of this macrogroup with low sagebrush density. Microphytic crust is very important for soil moisture retention, mitigating soil erosion, and seed germination in communities of this macrogroup.

Healthy montane sagebrush shrublands can be quite productive (roughly 100-150 gC m-2 year-1), though productivity is correlated with precipitation during the growing season. They are often grazed by domestic livestock, and are strongly preferred during the growing season (Padgett et al. 1989). Prolonged livestock use can cause a decrease in net primary productivity as well as the abundance of native bunchgrasses. It can also increase the canopy cover of shrubs and non-native grass species such as Bromus tectorum and Poa pratensis. Artemisia cana resprouts vigorously following spring fire, and prescribed burning may increase shrub cover. Conversely, fire in the fall may decrease shrub abundance (Hansen et al. 1995).

Artemisia tridentata is top-killed by fire and will not resprout Stands re-establish from seedbanks or from off-site sources depending on severity of burn and usually takes over ten years for it to form occurrences having 20% or more cover. However, a study on Wyoming big sagebrush shrub-steppe in central and southeast Montana stands where median time since fire was 22 years (ranging from 4 to 67 years) found no Wyoming big sagebrush canopy cover recovery for 17 of the 24 sites, and the oldest burn was only 8% recovered (Cooper et al. 2007). Lesica et al. (2005) did a similar study in southwest Montana with similar findings. Wyoming big sagebrush stands tend to occur on drier sites than the other subspecies and may be slower to recover on drier sites (Howard 1999). Tirmenstein (1999c) and Howard (1999) found sites with high-severity or repeated burns that kill the banked sagebrush seeds and mycorrhizal spores are slow to establish new shrubs so severity of fire and other fire characteristics, such as seasonality, size/extent, complexity, intensity, and type of fire as well as fire-return interval, influence post-fire recovery. According to Johnson (2000b), fire-return intervals of 30-70 years maintain perennial bunchgrasses and non-sprouting shrubs like sagebrush; fire-return intervals of 10-30 years eliminate short-lived, sprouting shrubs; and fire-return intervals of 2-5 years eliminate perennial grasses and non-sprouting shrubs leaving invasive annual grasses and forbs.

The condition of most sagebrush steppe has been degraded due to fire suppression, overgrazing by livestock, invasion by pinyon and juniper, and the invasion and subsequent domination of the herbaceous canopy by Bromus tectorum. It is unclear how long it will take to restore degraded occurrences.
Environmental Description: Climate: Climate ranges from semi-arid in the western Great Basin to subhumid in the northern plains and Rocky Mountains with much of the precipitation falling primarily as snow. Temperatures are continental with large annual and diurnal variations. Annual precipitation ranges from 18-40 cm in semi-arid areas and up to 90 cm in montane and subalpine zones. Growing-season drought is common. The amount and reliability of growing-season moisture increase eastward and with higher elevation.

Physiography/landform: This shrubland and shrub-steppe macrogroup is widely distributed in the western U.S., at elevations as low as 300 m in the Okanagan Valley of British Columbia and 500 m in the northwestern Great Plains and up to 2500 m in the Rocky Mountains and Colorado Plateau. All aspects are represented, but the occurrences at higher elevations may be restricted to south- or west-facing slopes. Xeric stands occur on flat to steeply sloping upland slopes on alluvial fans and terraces, toeslopes, lower and middle slopes, draws, badlands, foothills, and rocky slopes. Mesic stands occur on stream terraces, point bars, valley floors, alluvial fans, floodplains, washes, gullies, stabilized dunes, mesic uplands, and swales. Montane stands occur on stony flats, broad ridgetops, and mountain slopes.

Soil/substrate/hydrology: Soils vary from deep and well-developed to shallow, rocky and poorly developed substrates. Soil textures range from sands to loam and clay loams, and silt derived from alluvium, loess, shale, and sandstone. There is often a significant amount of coarse fragments in the soil profile. Montane soils tend to be moderately deep and well-drained, often with high volume of coarse fragments. In drier regions, these shrublands are usually associated with perennial or ephemeral stream drainages with water tables less than 3 m from the soil surface. In British Columbia stands often occur on lacustrine soils with silty textures.
Geographic Range: This shrubland and shrub-steppe macrogroup is widely distributed from the Great Basin, Columbia River Basin, Colorado Plateau, Rocky Mountains, northeastern Great Plains and as far east as the Dakotas and into British Columbia in some southern valleys.
Nations: CA, US
States/Provinces: AZ?, BC, CA, CO, ID, MT, ND, NM, NV, OR, SD?, UT, WA, WY
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name: Southwest Plateau and Plains Dry Steppe and Shrub Province
Province Code: 315    Occurrence Status: Confident or certain
Section Name: Yellowstone Highlands Section
Section Code: M331A     Occurrence Status: Confident or certain
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: High
Confidence Level Comments:
Grank: GNR
Greasons:
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: > Artemisia cana ssp. bolanderi Communities (Young et al. 2007a)
> Artemisia tridentata ssp. tridentata Communities (Young et al. 2007a)
> Artemisia tridentata ssp. vaseyana Communities (Young et al. 2007a)
> Artemisia tridentata ssp. wyomingensis Communities (Young et al. 2007a)
> Artemisia tridentata Communities (Young et al. 2007a)
> Artemisietalia tridendatae (Rivas-Martínez 1997)
> Antelope Bitterbrush - Bluebunch Wheatgrass (104) (Shiflet 1994) [Purshia tridentata shrublands are included in this macrogroup.]
> Antelope Bitterbrush - Idaho Fescue (105) (Shiflet 1994) [Purshia tridentata shrublands are included in this macrogroup.]
> Basin Big Sagebrush (401) (Shiflet 1994) [This is the primary macrogroup crosswalking to this SRM type.]
> Big Sagebrush - Bluebunch Wheatgrass (314) (Shiflet 1994)
> Big Sagebrush - Idaho Fescue (315) (Shiflet 1994)
> Bitterbrush (210) (Shiflet 1994) [Purshia tridentata steppe is included in this macrogroup.]
> Bitterbrush - Bluebunch Wheatgrass (317) (Shiflet 1994) [Bitterbrush-dominated communities are included in the big sage steppe macrogroup.]
> Bitterbrush - Idaho Fescue (318) (Shiflet 1994) [Bitterbrush-dominated communities are included in the big sage steppe macrogroup.]
> Bitterbrush - Rough Fescue (319) (Shiflet 1994) [Bitterbrush-dominated communities are included in the big sage steppe macrogroup.]
< Great Basin Desertscrub, Sagebrush Series - 152.11 (Brown et al. 1979)
> Great Basin Desertscrub, Sagebrush Series, Artemisia tridentata Association - 152.111 (Brown et al. 1979)
> Great Basin Desertscrub, Sagebrush Series, Artemisia tridentata-Mixed Scrub-Grass Association - 152.112 (Brown et al. 1979)
> Great Basin Sagebrush (West and Young 2000)
> Great Basin-Colorado Plateau sagebrush semi-desert (West 1983a)
>< Other Sagebrush Types (408) (Shiflet 1994) [Artemisia tridentata ssp. spiciformis shrublands are included in this macrogroup.]
> Sagebrush - Grass (612) (Shiflet 1994) [Artemisia tridentata ssp. tridentata steppe communities are included in this macrogroup.]
> Sagebrush Steppe (West and Young 2000)
> Sagebrush association (Artemisietum tridentatae) (Billings 1945)
> Sagebrush community (Artemisia-Agropyron-Lepus Association) (Fautin 1946)
> Threetip Sagebrush (404) (Shiflet 1994) [Artemisia tripartita ssp. tripartita shrublands are included in this macrogroup in the northern Great Basin, Columbia Plateau and northern Rockies regions.]
> Threetip Sagebrush - Idaho Fescue (324) (Shiflet 1994) [Artemisia tripartita ssp. tripartita communities are included in this macrogroup.]
> Western Intermountain sagebrush steppe (West 1983c) [Range overlaps.]
Concept Author(s): Faber-Langendoen et al. (2014)
Author of Description: K.A. Schulz and M. Jennings
Acknowledgements: We have incorporated significant descriptive information previously compiled by M.E. Hall.
Version Date: 26Jan2016
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