Print Report
A3964 Rhus glabra - Rhus trilobata Central Rocky Mountain Montane-Foothill Shrubland Alliance
Type Concept Sentence: This shrubland alliance is characterized by a sparse to moderately dense shrub layer dominated by Rhus glabra or Rhus trilobata with a sparse to moderately dense herbaceous layer composed of grasses such as Aristida purpurea, Festuca idahoensis, and Pseudoroegneria spicata. It is found in the lower montane and foothill regions around the Columbia Basin, including river canyons, and extends north and east into the Central Rockies and to the foothills and breaks in the western Great Plains.
Common (Translated Scientific) Name: Smooth Sumac - Skunkbush Sumac Central Rocky Mountain Montane-Foothill Shrubland Alliance
Colloquial Name: Central Rocky Mountain Montane-Foothill Sumac Shrubland
Hierarchy Level: Alliance
Type Concept: The vegetation is characterized by a sparse to moderately dense shrub layer dominated by Rhus glabra or Rhus trilobata. The sparse to moderately dense herbaceous layer is composed of Aristida purpurea var. longiseta, Festuca idahoensis, Pseudoroegneria spicata, and other graminoids or forbs. This shrubland alliance is found in the lower montane and foothill regions around the Columbia Basin, including river canyons, and extends north and east into the Central Rockies and to the foothills and breaks in the western Great Plains. Stands occur on a variety of sites, including steep lower slopes in canyons and valley bottoms where gravel and boulder colluvium accumulates, near talus slopes as garlands, at the heads of dry drainages, and toeslopes in the moist shrub-steppe zones. Stands also occur in patches or strips along the shoulder slopes of river breaks. Soils are often shallow and rocky.
Diagnostic Characteristics: The vegetation is characterized by the dominance of diagnostic species Rhus glabra or Rhus trilobata. High-constancy associated graminoid species consist primarily of Aristida purpurea var. longiseta, Festuca idahoensis, or Pseudoroegneria spicata.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: It is often difficult to determine the borders of stands within this alliance because one of the primary distinguishing features of this alliance, the presence of a 10-25% canopy of Rhus trilobata, is not continuous over the entire stand (Johnson and Simon 1987). When grassland communities adjoin stands of this alliance, they usually contain many of the same species. The presence and approximate limits of stands within this alliance is judged from physiognomic and sometimes floristic differences between adjacent stands. In the dry environments in which stands of this alliance are found, certain species not commonly found in the open grow in the shade of shrubs (Hansen and Hoffman 1988).
In his Rhus aromatica ssp. trilobata Series, Johnston (1987) described two other plant associations with Sporobolus cryptandrus- and Muhlenbergia montana-dominated herbaceous layers that need to be reviewed for possible inclusion into this alliance. Grasslands with clumps of Rhus trilobata are common in the foothills of the Colorado Front Range and also need association-level classification and review for possible inclusion in this alliance.
In his Rhus aromatica ssp. trilobata Series, Johnston (1987) described two other plant associations with Sporobolus cryptandrus- and Muhlenbergia montana-dominated herbaceous layers that need to be reviewed for possible inclusion into this alliance. Grasslands with clumps of Rhus trilobata are common in the foothills of the Colorado Front Range and also need association-level classification and review for possible inclusion in this alliance.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation in this alliance has a sparse to dense, sometimes patchily distributed layer of cold-deciduous shrubs (10-85% cover) that are less than 2 m tall with the sparse to moderately dense herbaceous layer dominated by perennial graminoids, mostly bunch grasses. There is also a sparse cover of perennial forbs. Annual forbs and grasses are seasonally present.
Floristics: This shrubland alliance is characterized by a short (~1 m tall), relatively sparse to moderately dense (10-60% cover), broad-leaved deciduous shrub layer that is dominated by Rhus glabra or Rhus trilobata (Mueggler and Stewart 1980, Hansen and Hoffman 1988). However, the shrub layer may range up to 85% cover and exceed 3 m in protected sites (Johnson and Simon 1987). Small amounts of other shrubs, such as Artemisia tridentata, Chrysothamnus spp., Prunus virginiana, Ribes cereum, Symphoricarpos occidentalis, and dwarf-shrubs Artemisia frigida, Gutierrezia sarothrae, Rosa spp., or Yucca glauca, may also be present. The herbaceous cover ranges from sparse to moderately dense (5-60% cover) and is often dominated by Aristida purpurea var. longiseta, Festuca idahoensis, or Pseudoroegneria spicata (Brown 1971, Mueggler and Stewart 1980, Thilenius et al. 1995). Other characteristic species include graminoids such as Bouteloua curtipendula, Bouteloua gracilis, Calamovilfa longifolia, Carex filifolia, Carex inops ssp. heliophila, Dalea purpurea, Hesperostipa comata, Koeleria macrantha, Muhlenbergia cuspidata, Pascopyrum smithii, Poa secunda, Schizachyrium scoparium, and Sporobolus cryptandrus, and forbs such as Achillea millefolium, Artemisia dracunculus, Astragalus inflexus, Echinacea angustifolia, Erigeron pumilus, Eriogonum spp., Gaura coccinea, Heterotheca villosa, Liatris punctata, Lomatium macrocarpum, Opuntia polyacantha, Phacelia heterophylla, Phlox hoodii, Phlox colubrina, Scutellaria angustifolia, Sphaeralcea coccinea, and Symphyotrichum ericoides (Brown 1971, Mueggler and Stewart 1980, Thilenius et al. 1995). Mosses and lichens are present and average about 5% cover. Exotic species, namely Bromus tectorum, Bromus arvensis (= Bromus japonicus), and Bromus briziformis, are often present and may dominate the herbaceous layer of some disturbed stands. Cover of nonvascular plants such as Selaginella densa may be common on grazed stands (DeVelice et al. 1995).
Dynamics: The dominant shrubs Rhus glabra and Rhus trilobata are adapted to tolerate fires. It is rarely killed when burned and sprouts vigorously from underground rhizomes following a fire (FEIS 1998, Mueggler and Stewart 1980). Vegetative reproduction is the primary mode of re-establishment after fire; however, Rhus glabra and Rhus trilobata may also reproduce through seed. Fire has variable effects on Pseudoroegneria spicata bunch grasses. Plants usually survive burning and growth is often stimulated, except when fire occurs in the driest month when the crowns will burn because of low moisture in the vegetation and the meristems are damaged (Johnson and Simon 1987). In fact, post-fire sprouts and seedlings may not compete well with grassland vegetation, and frequent fire is thought to exclude Rhus glabra from grasslands (Johnson and Simon 1987). Stands occur on rocky slopes that are likely to have few fires (Johnson and Simon 1987).
Livestock grazing does not impact stands on the steeper slopes, but where stands are more accessible, heavy summer use will reduce the abundance of the more palatable species such as Pseudoroegneria spicata, Festuca idahoensis and Hesperostipa comata. Less palatable species such as Artemisia frigida, Heterotheca villosa, and Achillea millefolium will increase. Rhus trilobata may also be favored by continued overgrazing (Mueggler and Stewart 1980).
The biggest threat is exotic plants that have invaded many stands. Common exotics include annual grasses such as Bromus tectorum, Bromus arvensis, and Bromus briziformis, and the perennial forbs Hypericum perforatum and Conyza canadensis. Bromus tectorum often occurs in these stands and contributes significant cover on sites disturbed by livestock or small mammals (Mueggler and Stewart 1980).
Livestock grazing does not impact stands on the steeper slopes, but where stands are more accessible, heavy summer use will reduce the abundance of the more palatable species such as Pseudoroegneria spicata, Festuca idahoensis and Hesperostipa comata. Less palatable species such as Artemisia frigida, Heterotheca villosa, and Achillea millefolium will increase. Rhus trilobata may also be favored by continued overgrazing (Mueggler and Stewart 1980).
The biggest threat is exotic plants that have invaded many stands. Common exotics include annual grasses such as Bromus tectorum, Bromus arvensis, and Bromus briziformis, and the perennial forbs Hypericum perforatum and Conyza canadensis. Bromus tectorum often occurs in these stands and contributes significant cover on sites disturbed by livestock or small mammals (Mueggler and Stewart 1980).
Environmental Description: This shrubland alliance is found in the lower montane and foothill regions around the Columbia Basin, including river canyons, and extends north and east into the Central Rockies and to the foothills and breaks in the western Great Plains. Valley bottom and canyon sites range from less than 200 m to slightly over 610 m elevation, while sites in the surrounding plateaus and mountains may be over 2700 m. Plains sites range from 1000-1400 m elevation. The climate is temperate, relatively xeric and continental. The east slope and plains sites have a mean annual precipitation of 33-50 cm with most of the precipitation (75%) occurring during the growing season from April to September. Columbia Basin sites have a mean annual precipitation of approximately 25-30 cm that primarily occurs in the winter as snow or rain. This moisture is stored in the fractures in the highly weathered bedrock and utilized during the typically dry summers. Stands are typically found on steep footslopes and toeslopes in canyons, valley bottoms where gravel and boulder colluvium accumulates, near talus slopes as garlands, at the heads of dry drainages, and toeslopes in the moist shrub-steppe zones. Stands also occur in patches or strips along the shoulder slopes of river breaks (but may extend to the footslopes), and on gently rolling to steep, rocky hillsides (Mueggler and Stewart 1980, Hansen and Hoffman 1988, MTNHP 1988). Sites are predominately on hot, dry southern to western aspects, although it may occur on all aspects.
Soils are typically shallow to moderately deep, well-drained, neutral to slightly alkaline (pH 7-7.9) loams or sandy loams that often have a high percentage of rock fragments (greater than 35% by volume and 50% ground cover). However, some valley bottom sites have deep, nearly stone-free, sandy alluvial soils (Hansen and Hoffman 1988, Thilenius et al. 1995). In the Columbia Basin parent materials are colluvium and alluvium derived from basalt, metabasalt, or granitic colluvium and loess. The more common gravelly substrates are less stable than boulder-sized ones. Some stands are reported from colluvial talus cones. Northwestern plains substrates include calcareous sandstones, shales, porcelanite and occasionally extrusive volcanic rock (Brown 1971, DeVelice et al. 1995). A biological crust may be present on better sites with less disturbance, while litter may cover as much as 65% of the ground surface. Most stands of this association have been severely disturbed by livestock grazing and have been converted to a zootic climax, dominated by herbaceous annuals, such as Bromus tectorum, Bromus arvensis, and Erodium cicutarium.
Soils are typically shallow to moderately deep, well-drained, neutral to slightly alkaline (pH 7-7.9) loams or sandy loams that often have a high percentage of rock fragments (greater than 35% by volume and 50% ground cover). However, some valley bottom sites have deep, nearly stone-free, sandy alluvial soils (Hansen and Hoffman 1988, Thilenius et al. 1995). In the Columbia Basin parent materials are colluvium and alluvium derived from basalt, metabasalt, or granitic colluvium and loess. The more common gravelly substrates are less stable than boulder-sized ones. Some stands are reported from colluvial talus cones. Northwestern plains substrates include calcareous sandstones, shales, porcelanite and occasionally extrusive volcanic rock (Brown 1971, DeVelice et al. 1995). A biological crust may be present on better sites with less disturbance, while litter may cover as much as 65% of the ground surface. Most stands of this association have been severely disturbed by livestock grazing and have been converted to a zootic climax, dominated by herbaceous annuals, such as Bromus tectorum, Bromus arvensis, and Erodium cicutarium.
Geographic Range: This shrubland alliance is found in the lower montane and foothill regions around the Columbia Basin, including the Salmon, Snake and Imnaha river canyons, and extends north and east into the Central Rockies and to the foothills and breaks in the western and northwestern Great Plains steppe of Montana and Wyoming.
Nations: US
States/Provinces: ID, MT, OR, WA, WY
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.900015
Confidence Level: Moderate
Confidence Level Comments: No Data Available
Grank: GNR
Greasons: No Data Available
Concept Lineage: A.1536 (in part) and A.1537 (in part). This new alliance includes associations from Old Alliance V.A.7.N.g. Rhus glabra Shrub Herbaceous Alliance (A.1536) and Old Alliance V.A.7.N.g. Rhus trilobata Shrub Herbaceous Alliance (A.1537).
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: > Rhus aromatica ssp. trilobata Series (Johnston 1987) [USFS Region 2 is mostly outside the central Rocky Mountains and includes two habitat types not described in this alliance: a subalpine type in Colorado and a sandy plains type in Oklahoma,]
> Rhus glabra Series (Tisdale 1986)
> Rhus trilobata Series (Mueggler and Stewart 1980)
> Rhus glabra Series (Tisdale 1986)
> Rhus trilobata Series (Mueggler and Stewart 1980)
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