Invalid Unit Specified
D022 Acer glabrum / Danthonia intermedia - Thalictrum occidentale Western North American Grassland & Shrubland Division

The U.S. National
Vegetation Classification
Type Concept Sentence: This division contains cool-temperate lowland to subalpine shrubland, grassland, and meadow communities that are dominated by cold-deciduous shrubs or cool-season bunchgrasses or mesic forbs in the mountainous regions of western North America, from Alaska's Aleutian Islands south to the central coast of California, and down through the Intermountain West ranges and Rocky Mountains to Arizona and New Mexico.
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Common (Translated Scientific) Name: Rocky Mountain Maple / Timber Oatgrass - Western Meadowrue Western North American Grassland & Shrubland Division
Colloquial Name: Western North American Grassland & Shrubland
Hierarchy Level: Division
Type Concept: This division is a mix of cool-temperate lowland and montane shrubland and grassland communities that are dominated by cold-deciduous shrubs and cool-season (C3) grasses, mesic forbs, and occasionally evergreen shrubs. It is widely distributed in the mountainous regions of the western US extending from Alaska's Aleutian Islands and Canada south to the lee side of the central coast of California, and down through the Intermountain West ranges and Rocky Mountain cordillera to Arizona and New Mexico. These are moist-mesic montane shrublands of interior cool slopes and canyons from 300 to 1650 m in elevation. They can form high cover and extensive stands of mostly tall deciduous shrubs. Strong diagnostic species that are often dominant or codominant include Acer glabrum, Amelanchier utahensis, Ribes cereum, and Symphoricarpos oreophilus. Moderate diagnostics include Holodiscus discolor, Holodiscus dumosus, Menziesia ferruginea, Physocarpus malvaceus, Physocarpus monogynus, Rosa nutkana, Rosa woodsii, and Vaccinium ovalifolium. These species can also be common constituents of adjacent mesic forests and woodlands, or as successional elements following fire or logging. Drier sites may be dominated by a mix of deciduous and evergreen shrubs and dwarf-shrubs. At higher elevations (600-2011 m), Vaccinium myrtillus, Vaccinium scoparium, and Vaccinium membranaceum are strong diagnostics with Arctostaphylos uva-ursi and Juniperus communis often prevalent. There are large swaths of dry-mesic shrublands at lower elevations (1500-2700 m) where the strong diagnostic dominants are Amelanchier utahensis, Cercocarpus montanus, Quercus gambelii, Quercus x pauciloba, Purshia stansburiana, Purshia tridentata, Ribes cereum, and Robinia neomexicana. In contrast, the division also includes moist-mesic lowland (<1000 m) shrublands along the northwest coast of the continent where Alnus viridis ssp. fruticosa, Rubus spectabilis, Salix barclayi, and Vaccinium ovalifolium are moderate regional diagnostic shrubs along with Athyrium filix-femina, Heracleum maximum, and Veratrum viride, or a variety of other moist-mesic herbaceous species.

Coastal and montane grasslands and mesic meadows of the division tend to lack a strong tall-shrub component under low-disturbance conditions. The mesic meadows are typified by high herbaceous cover and a rich complement of forbs and graminoids. Strong diagnostic forb species include Erigeron speciosus, Osmorhiza occidentalis, Senecio hydrophiloides, Senecio serra, Senecio triangularis, and Thalictrum occidentale. Mesic graminoids form a lesser component; common moderate diagnostic species include Bromus carinatus, Bromus sitchensis, Carex hoodii, Carex microptera, and Festuca viridula. Mesic meadow stands occur on moderate to steep slopes, glacio-fluvial flats, and valley bottoms at high elevations where snow cover persists relatively late in the season (>600 m to the north; <3350 m to the south). The soils are typically seasonally moist to saturated in the spring but, if so, will dry out later in the growing season. Many occurrences are small-patch in spatial character, and are often found in mosaics with woodlands, more dense shrublands, or just below alpine communities.

Drier sites are dominated by cool-season bunchgrasses with a suite of dry-mesic forbs found in the inter-grass spaces. Danthonia intermedia is a strong diagnostic species with a suite of moderately diagnostic species that are regional dominants, e.g., Danthonia parryi, Festuca arizonica, Festuca campestris, Festuca idahoensis, Festuca thurberi, Muhlenbergia montana, and Pseudoroegneria spicata in montane and subalpine grasslands of the Rocky Mountains and Intermountain West; Festuca idahoensis ssp. roemeri and Danthonia californica in the far-west mountains. Forbs are diverse and tolerant of relatively dry conditions and include moderate diagnostics such as Erigeron simplex, Eriogonum umbellatum, Potentilla hippiana, and Solidago multiradiata. The grasslands occur on flat to rolling plains, in inter-montane parks, and on dry sideslopes, especially with south and west aspects. Soils are mostly fine-textured grasslands soils (Mollisols), but some sites are shallower, rocky and windswept. Most sites range from 2200 to 3000 m but extend to lower elevation foothills and plains (to 300 m). In contrast, along the west coast, these communities are found on low-elevation terraces and ridgeline balds on the dry (east) side of the mountain ranges.

Mesic grasslands and meadows can be prone to invasion by non-native naturalized forage species creating ruderal communities. Typical dominants include Anthoxanthum odoratum, Bromus inermis, Cynosurus echinatus, Dactylis glomerata, Holcus lanatus, Phleum pratense, Poa pratensis, and numerous other non-native herbaceous species such as Acroptilon repens, Cardaria draba, Carduus nutans, Centaurea spp., Cirsium arvense, Lepidium latifolium, Linum bienne, and Linaria spp. There are relatively few non-native temperate upland shrublands, but Cytisus scoparius, Genista spp., Cytisus striatus (or Cytisus scoparius), and Ulex europaeus can form shrublands best in less xeric regions.
Diagnostic Characteristics: This division is a mix of cool-temperate lowland and montane shrubland and grassland communities, which are dominated by cold-deciduous shrubs and cool-season (C3) grasses, and occasionally evergreen shrubs. Among mesic shrublands, Acer glabrum, Amelanchier utahensis, Ribes cereum, and Symphoricarpos oreophilus are strong diagnostics. Dwarf-shrubs such as Vaccinium myrtillus, Vaccinium scoparium, and Vaccinium membranaceum are also diagnostic, particularly at higher elevations. There are dry-mesic shrublands of lower elevations where the strong diagnostic dominants are Amelanchier utahensis, Cercocarpus montanus, Purshia stansburiana, Purshia tridentata, Quercus gambelii, Quercus x pauciloba, Ribes cereum, and Robinia neomexicana. Grasslands occur on drier sites as well and are dominated by cool-season bunchgrasses and dry-mesic forbs. Danthonia intermedia is a strong diagnostic species with a suite of moderately diagnostic species that are regional dominants, e.g., Danthonia parryi, Festuca campestris, Festuca idahoensis, Festuca arizonica, Festuca thurberi, Muhlenbergia montana, and Pseudoroegneria spicata in montane and subalpine grasslands of the Rocky Mountains and Intermountain West; Festuca idahoensis ssp. roemeri, Festuca viridula and Danthonia californica in the far-west mountains. Among forbs, moderate diagnostic species include Erigeron simplex, Eriogonum umbellatum, Potentilla hippiana, and Solidago multiradiata. Mesic grasslands and meadows can be prone to invasion by non-native naturalized forage species; typical dominants include Anthoxanthum odoratum, Bromus inermis, Cynosurus echinatus, Dactylis glomerata, Holcus lanatus, Phleum pratense, and Poa pratensis.
Rationale for Nominal Species or Physiognomic Features: Acer glabrum is well-distributed across the range of the division and represents the shrub component; Danthonia intermedia reflects the montane grassland elements and is the most widespread; Thalictrum occidentale is representative of the mesic meadow component of the division.
Classification Comments: This is a heterogeneous division in need of further revision at the macrogroup level to create more uniform sets of growth forms, diagnostic species, and climatic gradients that apply across the entire division. Currently, the division ranges from sea level to subalpine; precipitation ranges from 20 cm (desert) to 250 cm (rainforest) and varies from winter dominant to summer dominant; environments include coastal bluffs, rolling plains, valleys, wetlands, hillslopes and mountain peaks; vegetation physiognomy includes evergreen and deciduous shrublands, shrub-steppes, grasslands, and non-graminoid herbaceous meadows (all growth forms except trees).
Similar NVC Types:
D039 North American Warm Desert Scrub & Grassland, note:
D052 Western North American Temperate Cliff, Scree & Rock Vegetation, note:
D043 Western North American Alpine Tundra, note:
D023 Central North American Grassland & Shrubland, note:
D025 North American Boreal Grassland & Shrubland, note:
D027 Pacific North American Coastal Scrub & Herb Vegetation, note:
D327 Californian Scrub & Grassland, note:
Physiognomy and Structure: This division is a mix of cool-temperate lowland and montane shrubland and grassland communities that are dominated by cold-deciduous shrubs and cool-season (C3) grasses, mesic forbs, and occasionally evergreen shrubs. It includes evergreen and deciduous shrublands, shrub-steppes, grasslands, and non-graminoid herbaceous meadows (all growth forms except trees).
Floristics: There are moist-mesic montane shrublands that can form high-cover stands where the dominant strong diagnostic species are Acer glabrum, Amelanchier utahensis, Ribes cereum, and Symphoricarpos oreophilus. Moderate diagnostics include Holodiscus discolor, Holodiscus dumosus, Menziesia ferruginea, Physocarpus malvaceus, Physocarpus monogynus, Rosa nutkana, Rosa woodsii, and Vaccinium ovalifolium. Under the shrubs and in the inter-shrub spaces there may be a diverse assortment of mesic forbs and graminoids (e.g., Arnica sororia, Delphinium bicolor, Heracleum maximum, Luzula glabrata, Chamerion angustifolium, Hydrophyllum fendleri, which are moderate diagnostic species). Drier sites may be dominated by a mix of deciduous and evergreen shrubs and dwarf-shrubs. At higher elevations (600-2011 m), Vaccinium myrtillus, Vaccinium scoparium, and Vaccinium membranaceum are strong diagnostics with Arctostaphylos uva-ursi and Juniperus communis often prevalent. There are large swaths of dry-mesic shrublands at lower elevations (1500-2700 m) where the strong diagnostic dominants are Amelanchier utahensis, Cercocarpus montanus, Purshia stansburiana, Purshia tridentata, Quercus gambelii, Quercus x pauciloba, Ribes cereum, and Robinia neomexicana. In contrast, the division also includes moist-mesic lowland (<1000 m) shrublands along the northwest coast of the continent where Alnus viridis ssp. fruticosa, Rubus spectabilis, Salix barclayi, and Vaccinium ovalifolium are moderate regional diagnostic shrubs along with Athyrium filix-femina, Heracleum maximum, and Veratrum viride, or a variety of other moist-mesic herbaceous species. Mesic meadows are typified by high herbaceous cover; strong diagnostic forb species include Erigeron speciosus, Osmorhiza occidentalis, Senecio hydrophiloides, Senecio serra, Senecio triangularis, and Thalictrum occidentale. Mesic graminoids form a lesser component; common moderate diagnostic species include Bromus carinatus, Bromus sitchensis, Carex hoodii, and Carex microptera. Drier sites are dominated by cool-season bunchgrasses with a suite of dry-mesic forbs in found in the inter-grass spaces. Danthonia intermedia is a strong diagnostic species with a suite of moderately diagnostic species that are regional dominants, e.g., Danthonia parryi, Festuca arizonica, Festuca campestris, Festuca idahoensis, Festuca thurberi, Muhlenbergia montana, and Pseudoroegneria spicata in montane and subalpine grasslands of the Rocky Mountains and Intermountain West; Festuca idahoensis ssp. roemeri (= Festuca roemeri), Festuca viridula, and Danthonia californica in the far-west mountains. Forbs are diverse and tolerant of relatively dry conditions and include moderate diagnostics such as Erigeron simplex, Eriogonum umbellatum, Potentilla hippiana, and Solidago multiradiata; moderate diagnostics include Valeriana sitchensis, Erigeron formosissimus, and Geum macrophyllum. Mesic grasslands and meadows can be prone to invasion by non-native naturalized forage species creating ruderal communities. Typical dominants include Anthoxanthum odoratum, Bromus inermis, Cynosurus echinatus, Dactylis glomerata, Holcus lanatus, Phleum pratense, Poa pratensis, and numerous other non-native herbaceous species such as Acroptilon repens, Cardaria draba, Carduus nutans, Centaurea spp., Cirsium arvense, Lepidium latifolium, Linum bienne, and Linaria spp. There are relatively few non-native temperate upland shrublands, but Cytisus scoparius, Genista spp., Cytisus striatus (or Cytisus scoparius), and Ulex europaeus can form shrublands best in less xeric regions.
Dynamics: The species in the shrublands and mesic meadows can also be common constituents of adjacent mesic forests and woodlands, or as successional elements following fire or logging. The grasslands tend to have a fire regime with rapid fire return that slows or sets back shrub invasion and maintains a low or patchy shrub distribution. Fire frequency is presumed to be less than 20 years. Shrublands have a fire regime with a longer fire-return interval or fire-adapted shrubs such as Physocarpus malvaceus, Cercocarpus montanus, Quercus gambelii (clonal), and Robinia neomexicana. Mesic meadow stands are typically not affected by fire due to moist conditions and surrounding rocky terrain. Natural processes affecting stands include fluctuating summer snowbanks (drought sequences), snow avalanches, and rockfalls. Burrowing mammals in places will disrupt the soil and vegetation locally.
Environmental Description: Environments are highly variable and include coastal bluffs, rolling plains, valleys, wetlands, hillslopes and mountain peaks. Moist-mesic montane shrublands occur on interior cool slopes and canyons from 300 to 1650 m in elevation. Mesic meadow stands occur on moderate to steep slopes, glacio-fluvial flats, and valley bottoms at high elevations where snow cover persists relatively late in the season (>600 m to the north; <3350 m to the south). They can also occur on gentle slopes with ample early-season seepage. The soils are typically seasonally moist to saturated in the spring but, if so, will dry out later in the growing season. Many occurrences are small-patch in spatial character, and are often found in mosaics with woodlands, more dense shrublands, or just below alpine communities. The grasslands occur on flat to rolling plains, in inter-montane parks, and on dry sideslopes, especially with south and west aspects. Grassland soils are mostly fine-textured grasslands soils (Mollisols), but some sites are shallower, rocky and windswept. Most sites range from 2200 to 3000 m but extend to lower-elevation foothills and plains (to 300 m). In contrast, along the west coast, these communities are found on low-elevation terraces and ridgeline balds on the dry (east) side of the mountain ranges.

Precipitation ranges from 20 cm (desert) to 250 cm (rainforest) and varies from winter dominant (west) to summer dominant (south and east).
Geographic Range: This division is widely distributed in the mountainous regions of the western U.S. extending from Alaska's Aleutian Islands and Canada south to the lee side of the central coast of California, and down through the Intermountain West ranges and Rocky Mountain cordillera to Arizona and New Mexico.
Nations: CA, US
States/Provinces: AB, AK, AZ, BC, CA, CO, ID, MT, NE, NM, NV, OR, SD, UT, WA, WY
US Forest Service Ecoregions (2007)
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Plot Analysis Summary:
Confidence Level: Low
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Grank: GNR
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Synonomy: >< Cold Temperate Grassland (Brown et al. 1998) [Their Rocky Mountain Montane Grassland and Oregon (Pacific Coastal) Grassland Biotic communities are included here.]
>< Cold Temperate Scrubland (Brown et al. 1998) [Their Great Basin Montane Scrub Biome Biotic Community are included here.]
> Mountain Mahogany - Oak Scrub (West and Young 2000)
> meadows and parks (Peet 2000)
Concept Author(s): D.E. Brown, F. Reichenbacher, and S. E. Franson (1998)
Author of Description: E.H. Muldavin
Acknowledgements: Marion Reid
Version Date: 13Jan2016
References:
  • Brown, D. E., F. Reichenbacher, and S. E. Franson. 1998. A classification of North American biotic communities. The University of Utah Press, Salt Lake City. 141 pp.
  • Faber-Langendoen, D., J. Drake, S. Gawler, M. Hall, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, and P. Comer, editors. 2010-2019a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
  • Peet, R. K. 2000. Forests and meadows of the Rocky Mountains. Chapter 3 in: M. G. Barbour and W. D. Billings, editors. North American terrestrial vegetation. Second edition. Cambridge University Press, New York. 434 pp.
  • West, N. E., and J. A. Young. 2000. Intermountain valleys and lower mountain slopes. Pages 255-284 in: M. G. Barbour and W. D. Billings, editors. North American Terrestrial Vegetation, second edition. Cambridge University Press, Cambridge.