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A3395 Pseudotsuga menziesii - Pinus ponderosa / Herbaceous Understory Central Rocky Mountain Woodland Alliance

Type Concept Sentence: This alliance represents montane coniferous forests found in the interior Pacific Northwest that are dominated by a mix of Pseudotsuga menziesii and Pinus ponderosa (but there can be stands without the latter) with a grass-dominated understory.


Common (Translated Scientific) Name: Douglas-fir - Ponderosa Pine / Herbaceous Understory Central Rocky Mountain Woodland Alliance

Colloquial Name: Central Rocky Mountains Douglas-fir - Ponderosa Pine / Herb Woodland

Hierarchy Level:  Alliance

Type Concept: Most occurrences of this montane coniferous forest alliance are dominated by a mix of Pseudotsuga menziesii and Pinus ponderosa (but there can be stands without the latter) and sometimes with other species, including Pinus contorta, Pinus monticola, Populus tremuloides, and Larix occidentalis. The understory is dominated by the herbaceous layer, usually graminoids, such as Calamagrostis rubescens, Carex geyeri, Carex rossii, Festuca campestris, Festuca idahoensis, Festuca occidentalis, and Pseudoroegneria spicata, but also ferns such as Aspidotis densa, and the forbs Balsamorhiza sagittata and Achillea millefolium may also be abundant. This alliance is found in the interior Pacific Northwest, from southernmost interior British Columbia, eastern Washington, eastern Oregon, northern Idaho, western and northern Montana, and south along the east slope of the Cascades in Washington and Oregon and ranges in Wyoming and northern Utah. It is associated with a submesic climate regime with annual precipitation ranging from 40 to >150 cm, with a maximum in winter or late spring. Winter snowpacks typically melt off in early spring at lower elevations. Elevations range from 460 to 2400 m (1500-7900 feet). Stands occur on cool, dry sites on mid to upper slopes, steep slopes, ridgelines, rocky sites and benches on all aspects. Slopes can be moderate to steep (3-60%), and soils are derived from pumice ash, lava, tuff, and granitic. Surface rocks can be abundant. It can be associated with glacial outwash or till in cold-air drainages.

Diagnostic Characteristics: Woodlands characterized by dominance of Pseudotsuga menziesii or codominated by Pinus ponderosa with understories typically dominated by graminoids, such as Calamagrostis rubescens, Carex geyeri, Carex rossii, and Pseudoroegneria spicata. Stands with the fern Aspidotis densa, an endemic indicator species for serpentine soils, are included in this alliance. The moderately dense herbaceous layer is dominated by the perennial bunchgrass Pseudoroegneria spicata (averaging 20% cover), with the forbs Balsamorhiza sagittata and Achillea millefolium contributing another 10%. Several other herbaceous species occur with patchy distribution within stands, occasionally having as much as 15% cover.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Included in this alliance are three wide-ranging, broadly defined associations: ~Pseudotsuga menziesii / Carex geyeri Forest (CEGL000430)$$, ~Pseudotsuga menziesii / Festuca idahoensis Woodland (CEGL000900)$$, and ~Pseudotsuga menziesii / Pseudoroegneria spicata Woodland (CEGL000908)$$, that also occur in the southern Rocky Mountains and will need to be reviewed.

Similar NVC Types: No Data Available
note: No Data Available

Physiognomy and Structure: Vegetation included in this alliance is characterized by an open to moderately dense canopy of evergreen needle-leaved trees 15-50 m tall. There is a sparse cover of understory trees (5-15 m tall). Shrubs (0.5-1 m tall) are typically sparse (<10% cover) as the understory is dominated by an open to dense herbaceous layer. This layer is usually dominated by perennial graminoids with forbs, but occasionally perennial forbs are dominant. Annual grasses and forbs are seasonally present.

Floristics: Most occurrences of this alliance are dominated by a mix of Pseudotsuga menziesii and Pinus ponderosa (but there can be stands without the latter) and sometimes with other species, including Pinus contorta, Pinus monticola, Populus tremuloides, and Larix occidentalis. At the southern end of the alliance''s range, scattered Abies concolor, Calocedrus decurrens, and Pinus lambertiana can be found in the stands, but Abies grandis will not be found, although trace amounts of Abies grandis may occur in northern portion of its range. The understory is characterized by a low to dense herbaceous layer, usually dominated by graminoids although scattered shrubs such as Amelanchier alnifolia, Paxistima myrsinites, Sorbus scopulina, and Symphoricarpos oreophilus and dwarf-shrubs such as Arctostaphylos uva-ursi and Mahonia repens may also be present. However, shrub cover is sparse and does not form a layer (<10% total cover) and herbaceous cover exceeds cover of shrubs. The herbaceous layer is composed of perennial bunchgrasses and dry sedges such as Calamagrostis rubescens, Carex geyeri, Carex rossii, Festuca campestris, Festuca idahoensis, Festuca occidentalis, and Pseudoroegneria spicata, but also ferns such as Aspidotis densa, and the forbs Balsamorhiza sagittata and Achillea millefolium may also be abundant. Other common species may include graminoids Achnatherum occidentale (= Stipa occidentalis), Bromus ciliatus, Koeleria macrantha, and Luzula parviflora. Other forbs include Apocynum androsaemifolium, Arnica cordifolia, Eriophyllum lanatum, Moehringia macrophylla (= Arenaria macrophylla), Osmorhiza berteroi, Pteridium aquilinum, Thalictrum occidentale, Viola adunca, and species of many other genera, including Arenaria, Erigeron, Eriogonum, Fragaria, Galium, Lathyrus, Lupinus, Penstemon, and Vicia. Scattered shrubs may be present.

Dynamics:  Vegetation within this alliance is often comprised of relatively young stands, which were historically subject to recurrent fires. Both Pinus ponderosa and Pseudotsuga menziesii are tolerant of surface fires, and many mature trees have fire scars. The fire frequency is 5-30 years. Fire suppression has favored Pseudotsuga menziesii, but canopy closure is rare because of the harshness of these sites (Williams et al. 1990b). In addition, Pseudotsuga menziesii is more tolerant than Pinus ponderosa. Following fire, regeneration of Pinus ponderosa is aggressive. With increasing stand age, Pseudotsuga menziesii comes to dominate regeneration and eventually attains canopy dominance. Some stands require fire or other disturbance at moderate return intervals to maintain a mixed canopy. For example, in northern stands, Abies grandis will eventually become the canopy dominant with fire suppression. This alliance also occurs as an edaphic climax on moderate to steep slopes, in canyons, and in places along the ecotone between the Pseudotsuga menziesii and Pinus ponderosa zones. The exotic grass Bromus tectorum often invades the herbaceous layer of disturbed stands.

Environmental Description:  This alliance is composed of montane coniferous forests found in the interior Pacific Northwest, from southernmost interior British Columbia, eastern Washington, eastern Oregon, northern Idaho, western and northern Montana, and south along the east slope of the Cascades in Washington and Oregon. Elevations range from 460 to 2400 m (1500-7900 feet). Climate is mostly temperate, continental with maritime influences and is strongly influenced by the rainshadow effect of the Cascade Range or Coast Ranges of southern Oregon. Winter snowpacks typically melt off in early spring at lower elevations. Annual precipitation ranges from 40 cm in the Blue Mountains, up to 150-230 cm in the Cascades. Sites are typically on hot, dry, middle to upper slopes near grassy ridgetops. Slopes are moderate to steep with typically southern to western aspects, but stands may occur on northern slopes at low elevations. Substrates are typically shallow, lithic, course-textured soils derived from colluvium and residuum. Soil texture ranges from gravelly sand to sandy loam. There is often high surface cover of rock (to 50%), and coarse fragments average 40%. Parent materials may include granitic till or outwash, basalt, lava, pumice ash, tuff, granitics and sandstone. These shallow soils have so little moisture-holding capacity that these sites are effectively very dry for plant growth despite the substantial input of precipitation on most sites. These sites are exposed to high winds. Wind detracts from soil moisture status by blowing off snow, directly desiccating plants, and eroding soil.

Geographic Range: This alliance is composed of montane coniferous forests found in the interior Pacific Northwest, from southernmost interior British Columbia, eastern Washington, eastern Oregon, northern Idaho, western and northern Montana, and south along the east slope of the Cascades in Washington and Oregon. Peripheral stands are found on relatively dry sites in the northern Cascades such as Mount Rainier.

Nations: CA,US

States/Provinces:  AB, BC, CO, ID, MT, OR, UT, WA, WY




Confidence Level: Low

Confidence Level Comments: No Data Available

Grank: GNR

Greasons: No Data Available

Type Name Database Code Classification Code
Class 1 Forest & Woodland Class C01 1
Subclass 1.B Temperate & Boreal Forest & Woodland Subclass S15 1.B
Formation 1.B.2 Cool Temperate Forest & Woodland Formation F008 1.B.2
Division 1.B.2.Nb Rocky Mountain Forest & Woodland Division D194 1.B.2.Nb
Macrogroup 1.B.2.Nb.2 Ponderosa Pine - Douglas-fir - Limber Pine Central Rocky Mountain Dry Forest Macrogroup M501 1.B.2.Nb.2
Group 1.B.2.Nb.2.b Douglas-fir - Ponderosa Pine Central Rocky Mountain Forest Group G210 1.B.2.Nb.2.b
Alliance A3395 Douglas-fir - Ponderosa Pine / Herbaceous Understory Central Rocky Mountain Woodland Alliance A3395 1.B.2.Nb.2.b
Association CEGL000207 Ponderosa Pine - Douglas-fir / Beardless Wheatgrass Woodland CEGL000207 1.B.2.Nb.2.b
Association CEGL000210 Ponderosa Pine - Douglas-fir / Pinegrass Woodland CEGL000210 1.B.2.Nb.2.b
Association CEGL000211 Ponderosa Pine - Douglas-fir / Geyer''s Sedge Forest CEGL000211 1.B.2.Nb.2.b
Association CEGL000429 Douglas-fir / Pinegrass Woodland CEGL000429 1.B.2.Nb.2.b
Association CEGL000430 Douglas-fir / Geyer''s Sedge Forest CEGL000430 1.B.2.Nb.2.b
Association CEGL000434 Douglas-fir / Western Fescue Forest CEGL000434 1.B.2.Nb.2.b
Association CEGL000544 Quaking Aspen - Douglas-fir / Pinegrass Forest CEGL000544 1.B.2.Nb.2.b
Association CEGL000847 Ponderosa Pine / Indian''s Dream Woodland CEGL000847 1.B.2.Nb.2.b
Association CEGL000896 Douglas-fir / Indian''s Dream Woodland CEGL000896 1.B.2.Nb.2.b
Association CEGL000900 Douglas-fir / Idaho Fescue Woodland CEGL000900 1.B.2.Nb.2.b
Association CEGL000901 Douglas-fir / Rough Fescue Woodland CEGL000901 1.B.2.Nb.2.b
Association CEGL000908 Douglas-fir / Bluebunch Wheatgrass Woodland CEGL000908 1.B.2.Nb.2.b

Concept Lineage: This alliance is based on A.NCCN-036 Pseudotsuga menziesii - (Pinus ponderosa) Forest Alliance. I have split this alliance further into shrub- and grass-dominated understory alliances. This new alliance is based in part on 6 old NVC alliances including Old Alliances I.A.8.N.b. Pinus ponderosa - Pseudotsuga menziesii Forest Alliance (A.134), I.A.8.N.b. Pinus ponderosa Forest Alliance (A.124), I.A.8.N.c. Pseudotsuga menziesii Forest Alliance (A.157), II.A.4.N.a. Pinus ponderosa - Pseudotsuga menziesii Woodland Alliance (A.533), II.A.4.N.a. Pinus ponderosa Woodland Alliance (A.530), II.A.4.N.b. Pseudotsuga menziesii Woodland Alliance (A.552)

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available

Synonomy: > Pinus ponderosa - Pseudotsuga menziesii / Agropyron spicatum Association (Williams and Lillybridge 1985)
> Pinus ponderosa / Agropyron spicatum - Aspidotis densa (Lillybridge et al. 1995)
> Pinus ponderosa / Agropyron spicatum - Aspidotis densa Plant Association (Williams and Smith 1990)
> Pseudotsuga menziesii / Agropyron spicatum Community Type (Cole 1982)
> Pseudotsuga menziesii / Calamagrostis rubescens Habitat Type (Cooper et al. 1987)
> Pseudotsuga menziesii / Calamagrostis rubescens Habitat Type (Pfister et al. 1977)
> Pseudotsuga menziesii / Calamagrostis rubescens Plant Association (Johnson and Clausnitzer 1992)
> Pseudotsuga menziesii / Festuca idahoensis Habitat Type (Steele et al. 1983)
> Pseudotsuga menziesii / Festuca occidentalis (Topik et al. 1988)

Concept Author(s): K.A. Schulz, in Faber-Langendoen et al. (2013)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 01-08-14

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  • Cooper, S. V., K. E. Neiman, R. Steele, and D. W. Roberts. 1987. Forest habitat types of northern Idaho: A second approximation. General Technical Report INT-236.USDA Forest Service, Intermountain Research Station, Ogden, UT. 135 pp. [reprinted in 1991]
  • Faber-Langendoen, D., J. Drake, M. Hall, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, M. Russo, K. Schulz, L. Sneddon, K. Snow, and J. Teague. 2013-2019b. Screening alliances for induction into the U.S. National Vegetation Classification: Part 1 - Alliance concept review. NatureServe, Arlington, VA.
  • Johnson, C. G., and R. R. Clausnitzer. 1992. Plant associations of the Blue and Ochoco mountains. R6-ERW-TP-036-92. USDA Forest Service, Pacific Northwest Region, Wallowa-Whitman National Forest. 163 pp. plus appendices.
  • Lillybridge, T. R., B. L. Kovalchik, C. K. Williams, and B. G. Smith. 1995. Field guide for forested plant associations of the Wenatchee National Forest. General Technical Report PNW-GTR-359. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. 335 pp.
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