Print Report

A3179 Purshia tridentata - Artemisia tridentata Mesic Steppe & Shrubland Alliance

Type Concept Sentence: This mesic alliance occurs throughout the Intermountain West and is characterized by an open to moderately dense short-shrub layer dominated or codominated by Purshia tridentata with Artemisia tridentata and sometimes Prunus virginiana present to codominant. The understory is sparse to dense and typically dominated by perennial bunchgrasses such as Achnatherum hymenoides, Achnatherum nelsonii, Achnatherum occidentale, Festuca campestris, Festuca idahoensis, Hesperostipa comata, Leymus cinereus, Poa secunda, and Pseudoroegneria spicata.

Common (Translated Scientific) Name: Antelope Bitterbrush - Big Sagebrush Mesic Steppe & Shrubland Alliance

Colloquial Name: Antelope Bitterbrush - Big Sagebrush Mesic Steppe & Shrubland

Hierarchy Level:  Alliance

Type Concept: This mesic shrubland and steppe alliance occurs throughout the Intermountain West and occurs over a broad range of landforms and microhabitats. Stands are characterized by an open to moderately dense short-shrub layer dominated or codominated by Purshia tridentata with Artemisia tridentata and sometimes Prunus virginiana present to codominant. Other important shrubs include Ericameria nauseosa, Eriogonum heracleoides, Ribes cereum, and Symphoricarpos oreophilus. The understory is sparse to dense and typically dominated by perennial bunchgrasses such as Achnatherum hymenoides, Achnatherum nelsonii, Achnatherum occidentale, Festuca campestris, Festuca idahoensis, Hesperostipa comata, Leymus cinereus, Poa secunda, and Pseudoroegneria spicata. Some stands may have a well-developed forb component composed of Arabis holboellii, Achillea millefolium, Balsamorhiza sagittata, Brodiaea spp., Eriogonum ovalifolium, Eriogonum umbellatum, Lithospermum ruderale, and Pteryxia terebinthina. Mosses and lichens are important in some stands. Scattered trees may form an emergent layer of individual trees. Stands occur on flats to moderate slopes in foothills, on slopes of lakebeds with ash or pumice soils, and on drier sites within lower forest zones as shrub-steppe inclusions in forest. In Idaho, the alliance is reported from stabilized dunes. In general, it is an upland type associated with coarse, well-drained soils without high salinity or pH. Adjacent vegetation is typically Artemisia steppe, Pseudoroegneria - Poa - Festuca grasslands, or Pinus flexilis woodlands.

Diagnostic Characteristics: Stands in this mesic shrubland and steppe alliance are dominated or codominated by Purshia tridentata with Artemisia tridentata and sometimes Prunus virginiana present to codominant. Characteristic herbaceous species are Achnatherum hymenoides, Achnatherum nelsonii, Achnatherum occidentale, Carex pensylvanica, Eriogonum umbellatum, Festuca campestris, Festuca idahoensis, Hesperostipa comata, Leymus cinereus, Poa secunda, and Pseudoroegneria spicata.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This mesic shrubland and steppe alliance occurs as large patch/matrix stands in relatively mesic northern latitudes. However, in semi-arid landscapes in more southern latitudes, it frequently occurs in smaller patch stands restricted to relatively mesic sites, such as swales and basins, that receive additional moisture from surrounding slopes and at higher elevations.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: This alliance has a moderately dense to open (20-60% cover) microphyllous evergreen (or late cold-deciduous) shrublands with the dominant shrubs varying from 0.5-3 m in height. Maximum shrub height generally decreases with latitude and altitude, reaching a minimum in subalpine stands. A second tier of microphyllous evergreen or cold-deciduous shrubs may be present. Cespitose graminoids are typical herbaceous associates and may strongly dominate the ground layer. Some regional variants may have a substantial forb component as well. Lichens and mosses may cover the ground surface in good condition stands.

Floristics: This mesic shrubland and steppe alliance is characterized by an open to moderately dense short-shrub layer dominated or codominated by Purshia tridentata with Artemisia tridentata and sometimes Prunus virginiana present to codominant. Other important or occasional shrubs include Artemisia frigida, Ceanothus velutinus, Chrysothamnus viscidiflorus, Ericameria nauseosa (= Chrysothamnus nauseosus), Eriogonum heracleoides, Ribes cereum, and Symphoricarpos oreophilus. Scattered trees may form an emergent layer of individual trees; species include Cercocarpus ledifolius, Juniperus occidentalis, Juniperus osteosperma, Juniperus scopulorum, Pinus ponderosa, Pinus jeffreyi, Pinus ponderosa var. washoensis (= Pinus washoensis), Quercus garryana, or Yucca brevifolia. The understory is sparse to dense and typically dominated by perennial bunchgrasses such as Achnatherum hymenoides, Achnatherum nelsonii, Achnatherum occidentale, Elymus lanceolatus, Festuca campestris, Festuca idahoensis, Hesperostipa comata, Koeleria macrantha, Leymus cinereus, , Poa secunda, and Pseudoroegneria spicata. Other graminoids include Carex geyeri, Carex pensylvanica, and Muhlenbergia montana. Some stands may have a well-developed forb component composed of Arabis holboellii, Achillea millefolium, Balsamorhiza sagittata, Brodiaea spp., Eriogonum ovalifolium, Eriogonum umbellatum, Lithospermum ruderale, and Pteryxia terebinthina (= Cymopterus terebinthinus). Mosses and lichens are important in some stands. Diagnostic of this alliance is the dominance of Purshia tridentata in a shrub layer that is greater than 25% on average.

Dynamics:  Purshia tridentata displays considerable plasticity in growth across its range. The variation in height and form of different populations appears to be related to ecotypic variation (Mozingo 1987). Although mycorrhizae are considered important in establishment and growth of individual plants, Purshia tridentata is one of the first species to colonize barren volcanic substrates following eruption. The species is valuable as winter browse for native ungulates and livestock and is used extensively. Moderate livestock utilization (<60% of the year''s current growth) has been reported to stimulate twig growth the following spring (Mueggler and Stewart 1980). Sawyer and Keeler-Wolf (1995) report that stands of Purshia tridentata can reach 125 years of age on deep, well-drained sites, but more commonly become decadent at 30 years, and die at 40-50 years of age. Stands appear to result from either a disturbance event (such as fire), or from rare years when many seedlings survive. This results in even-aged stands (Sawyer and Keeler-Wolf 1995).
Environmental Description:  This mesic shrubland and steppe alliance occurs throughout the Intermountain West over a broad range of landforms and microhabitats at elevations from 500-3000 m. Stands are often found on the margins of Pinus ponderosa woodlands or forests, forming the transition into sagebrush vegetation. Most of the region is arid to semi-arid with annual precipitation ranging from 15-75 cm. The entire range is under a continental temperature regime of cold winters, cool to warm summers and large diurnal variation. In the western portions of the alliance''s range, summers are dry. Growing-season precipitation increases eastward and is the greatest in the Rocky Mountains. They also occur on flats to moderate slopes in foothills, on slopes of lakebeds with ash or pumice soils, and on drier sites within lower forest zones as shrub-steppe inclusions in forest. In Idaho, the alliance is reported from stabilized dunes (Chadwick and Dalke 1965). In Colorado, the alliance is found on exposed, steep (45-60% slope) mountain slopes with southerly aspects on the eastern slopes of the Front Range (Hess 1981). These sites are typically too xeric to support extensions of the surrounding coniferous forests. Parent materials are colluvial and residual metamorphic rocks which have developed into soils classified as Entisols. These soils are poorly developed and rocky, with loamy and sandy textures, and shallow A horizons over rocky C horizons. The soil surface is also moderately rocky. In general, it is an upland type associated with coarse, well-drained soils without high salinity or pH. Adjacent vegetation is typically Artemisia steppe, Pseudoroegneria - Poa - Festuca grasslands, or Pinus flexilis woodlands.
Geographic Range: This alliance is found in many western U.S. states and Canada, from California north and east into Oregon, Washington, Idaho, Colorado and British Columbia. The core of its range is the Columbia Basin and Columbia Plateau, Owyhee Uplands, Snake River Plain, and the Colorado Rockies. Purshia tridentata is one of the most widespread shrubs in the western United States.

Nations: CA,US

States/Provinces:  BC, CA, ID, MT, NV, OR, UT, WA, WY


Confidence Level: Moderate

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 3 Desert & Semi-Desert Class C03 3
Subclass 3.B Cool Semi-Desert Scrub & Grassland Subclass S11 3.B
Formation 3.B.1 Cool Semi-Desert Scrub & Grassland Formation F033 3.B.1
Division 3.B.1.Ne Western North American Cool Semi-Desert Scrub & Grassland Division D040 3.B.1.Ne
Macrogroup 3.B.1.Ne.3 Big Sagebrush - Threetip Sagebrush - Antelope Bitterbrush Steppe & Shrubland Macrogroup M169 3.B.1.Ne.3
Group 3.B.1.Ne.3.b Basin Big Sagebrush - Threetip Sagebrush - Antelope Bitterbrush Big Sagebrush Steppe & Shrubland Group G302 3.B.1.Ne.3.b
Alliance A3179 Antelope Bitterbrush - Big Sagebrush Mesic Steppe & Shrubland Alliance A3179 3.B.1.Ne.3.b
Association CEGL001058 Antelope Bitterbrush / Indian Ricegrass Shrubland CEGL001058 3.B.1.Ne.3.b
Association CEGL001059 Antelope Bitterbrush / Sandberg Bluegrass Shrubland CEGL001059 3.B.1.Ne.3.b
Association CEGL001060 Antelope Bitterbrush / Chokecherry Shrubland CEGL001060 3.B.1.Ne.3.b
Association CEGL001492 Antelope Bitterbrush / Long-stolon Sedge - Western Needlegrass Shrub Grassland CEGL001492 3.B.1.Ne.3.b
Association CEGL001494 Antelope Bitterbrush / Rough Fescue Shrub Grassland CEGL001494 3.B.1.Ne.3.b
Association CEGL001495 Antelope Bitterbrush / Bluebunch Wheatgrass Shrub Grassland CEGL001495 3.B.1.Ne.3.b
Association CEGL001497 Antelope Bitterbrush / Bluebunch Wheatgrass - Basin Wildrye Shrub Grassland CEGL001497 3.B.1.Ne.3.b
Association CEGL001498 Antelope Bitterbrush / Needle-and-Thread Shrub Grassland CEGL001498 3.B.1.Ne.3.b
Association CEGL002674 Antelope Bitterbrush / Idaho Fescue Shrub Grassland CEGL002674 3.B.1.Ne.3.b
Association CEGL003477 Antelope Bitterbrush - Big Sagebrush / Sulphur-flower Buckwheat Shrubland CEGL003477 3.B.1.Ne.3.b
Association CEGL003478 Antelope Bitterbrush - Big Sagebrush / Indian Ricegrass Shrubland CEGL003478 3.B.1.Ne.3.b
Association CEGL003479 Antelope Bitterbrush - Big Sagebrush / Columbia Needlegrass Shrubland CEGL003479 3.B.1.Ne.3.b
Association CEGL003480 Antelope Bitterbrush - Big Sagebrush - Roundleaf Snowberry Shrubland CEGL003480 3.B.1.Ne.3.b
Association CEGL003481 Antelope Bitterbrush - Big Sagebrush - Spineless Horsebrush Shrubland CEGL003481 3.B.1.Ne.3.b
Association CEGL005610 Antelope Bitterbrush - Dwarf Goldenbush / Scabland Penstemon Shrubland CEGL005610 3.B.1.Ne.3.b
Association CEGL005611 Antelope Bitterbrush - Lewis'' Mock Orange / Sandberg Bluegrass Shrubland CEGL005611 3.B.1.Ne.3.b
Association CEGL005612 Antelope Bitterbrush / Thurber''s Needlegrass Shrubland CEGL005612 3.B.1.Ne.3.b
Association CEGL005613 Antelope Bitterbrush / Basin Wildrye Shrub Grassland CEGL005613 3.B.1.Ne.3.b
Concept Lineage: A.825, A.1517, A.1523. This alliance includes proto alliances Purshia tridentata Shrubland Alliance (A.825), Purshia tridentata Shrub Herbaceous Alliance (A.1523) and old alliances III.A.4.N.a. Purshia tridentata Shrubland Alliance (A.825), V.A.7.N.b. Purshia tridentata Shrub Tall Herbaceous Alliance (A.1517), V.A.7.N.e. Purshia tridentata Shrub Herbaceous Alliance (A.1523). and one association from old alliance III.A.4.N.a. Artemisia tridentata ssp. wyomingensis Shrubland Alliance (A.832).

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: > Purshia tridentata (Bitter brush scrub) Alliance (Sawyer et al. 2009) [35.200.00]
>< Bitterbrush Series (Sawyer and Keeler-Wolf 1995)
Concept Author(s): K.A. Schulz, in Faber-Langendoen et al. (2013)

Author of Description: K.A. Schulz

Acknowledgements: We have incorporated significant descriptive information previously compiled by D. Sarr.

Version Date: 12-18-14
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