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G217 Thuja plicata - Tsuga heterophylla Central Rocky Mountain Forest Group
Type Concept Sentence: This forest group occurs in the Northern Rockies west of the Continental Divide within the maritime-influenced climatic zone dominated by Tsuga heterophylla and Thuja plicata; Pseudotsuga menziesii commonly shares the canopy, and Abies grandis, Larix occidentalis, Pinus contorta, Pinus monticola, and Taxus brevifolia are major associates. The composition of shrub and herbaceous layers reflects local climate and degree of canopy closure and is typically highly diverse in all but closed-canopy conditions.
Common (Translated Scientific) Name: Western Red-cedar - Western Hemlock Central Rocky Mountain Forest Group
Colloquial Name: Central Rocky Mountain Interior Western Red-cedar - Western Hemlock Forest
Hierarchy Level: Group
Type Concept: This forest group occurs in the Northern Rockies west of the Continental Divide within the maritime-influenced climatic zone of the northern Rocky Mountains of western Montana, west into northeastern Washington and southern British Columbia. These are forests dominated by Tsuga heterophylla and Thuja plicata in most cases, found in areas influenced by incursions of mild, wet, Pacific maritime air masses. Much of the annual precipitation occurs as rain, 25-50% falls as snow. Snowpacks are often melted by rain during warm winter storms. Occurrences generally are found on all slopes and aspects but grow best on sites with high soil moisture, such as toeslopes and bottomlands. At the periphery of its distribution, this group is confined to moist canyons and cooler, moister aspects. Generally these are moist, non-flooded or upland sites that are not saturated yearlong. Along with Tsuga heterophylla and Thuja plicata, Pseudotsuga menziesii commonly shares the canopy, and Pinus monticola, Pinus contorta, Abies grandis, Taxus brevifolia, and Larix occidentalis are major associates. Cornus nuttallii may be present in some situations. Picea engelmannii, Abies lasiocarpa, and Pinus ponderosa may be present but only on the coldest or warmest and driest sites. Linnaea borealis, Mahonia nervosa, Paxistima myrsinites, Acer glabrum, Spiraea betulifolia, Symphoricarpos hesperius, Cornus canadensis, Rubus parviflorus, Menziesia ferruginea, and Vaccinium membranaceum are common shrub species. The composition of the herbaceous layer reflects local climate and degree of canopy closure; it is typically highly diverse in all but closed-canopy conditions. Important forbs and ferns include Actaea rubra, Achlys triphylla, Anemone piperi, Aralia nudicaulis, Asarum caudatum, Clintonia uniflora, Coptis occidentalis, Thalictrum occidentale, Tiarella trifoliata, Trientalis borealis, Trillium ovatum, Viola glabella, Gymnocarpium dryopteris, Polystichum munitum, and Adiantum pedatum. Typically, stand-replacement, fire-return intervals are 150-500 years, with moderate-severity fire intervals of 50-100 years. Species in East Cascade forests (G212) that are absent to rare in the Northern Rockies are Picea sitchensis, Abies amabilis, Acer macrophyllum, Acer circinatum, Gaultheria shallon, Rhododendron macrophyllum, Mahonia nervosa, Rubus spectabilis, Vaccinium alaskaense, Vaccinium parvifolium, Blechnum spicant, Achlys triphylla, Oxalis oregana, Anemone deltoidea, Anemone oregana, Rubus lasiococcus, and Streptopus streptopoides.
Diagnostic Characteristics: Productive and diverse forests dominated by Tsuga heterophylla and/or Thuja plicata in most cases, found in the interior of the Pacific Northwest, in areas influenced by incursions of mild, wet, Pacific maritime air masses. Floristic affinities are with the Rocky Mountains. These forests persist for centuries, having fire-return intervals often >500 years.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: Tsuga heterophylla is a major tree species in the Pacific Northwest, and there are many other groups where it is a dominant species. This group contains western hemlock and western red-cedar associations that are confined to the interior regions of the Northwest. Certainly, there are some floristic similarities between the Northern Rockies types and those found west of the Cascades. However, there''s a distinct "Rocky Mountain" set of species i.e., Anemone piperi, Aralia nudicaulis, Coptis occidentalis, found in this group. Further information needs to be included here for interior western hemlock and western red-cedar forests of British Columbia. Concept needs to be narrowed to remove the East Cascadian portion of this group.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: These are productive forests composed of tall, long-lived, needle-leaved evergreen trees, sometimes composed of just one tree species, but more often are of mixed composition. Deciduous tall and short shrubs, and perennial forbs and ferns often form shrub and herbaceous layers, respectively. These forests are the most diverse of any Rocky Mountain forest, sometimes approaching or equaling the within-stand diversity of some eastern North American forests, but the diversity resides in the shrub and herb taxa, not the trees.
Floristics: In addition to the dominant Tsuga heterophylla and Thuja plicata, Pseudotsuga menziesii and Abies grandis commonly share the canopy, and Pinus monticola, Pinus contorta, Abies grandis, Abies lasiocarpa, and Larix occidentalis are major associates. Picea engelmannii and Abies lasiocarpa may be present but only on the coldest sites, and Pinus ponderosa may be present but only on the warmest and driest sites. Common shrubs include Paxistima myrsinites, Acer glabrum, Spiraea betulifolia, Symphoricarpos albus, Cornus canadensis, Rubus parviflorus, Menziesia ferruginea, Taxus brevifolia, and Vaccinium membranaceum. Oplopanax horridus is common in the understory in depressional areas with high water tables. Composition of the herbaceous layer reflects local climate and degree of canopy closure; it is typically highly diverse in all but closed-canopy conditions. Clintonia uniflora, Tiarella trifoliata, Xerophyllum tenax, and Viola orbiculata are the most common forbs in these forests. Other forbs include Actaea rubra, Adenocaulon bicolor, Aralia nudicaulis, Arnica spp., Galium triflorum, Goodyera oblongifolia, Linnaea borealis, Orthilia secunda, Streptopus amplexifolius, Thalictrum occidentale, and Trillium ovatum. Asarum caudatum occurs in the Kootenai and Yak river areas of extreme northwestern Montana. Ferns and fern allies also form an important component of the understory and commonly include Athyrium filix-femina, Botrychium spp., Dryopteris filix-mas, Equisetum spp., Gymnocarpium dryopteris, and Polystichum munitum. Under closed-canopy conditions, a dense moss layer can form on the forest floor. Graminoids usually form a very minor component and typically include Bromus vulgaris, Carex deweyana, Carex geyeri, Elymus glaucus, Festuca subulata, and Oryzopsis asperifolia.
Dynamics: These are very productive forests which have been priority stands for timber production. Typically, stand-replacement fire-return intervals are 150-500 years in the Cascades, or 150-500 years in the Northern Rockies, with moderate-severity fire-return intervals of 50-100 years. Thuja and Tsuga are capable of remaining dominant within these forests due to their longevity and Thuja''s ability to regenerate vegetatively. In the absence of disturbance, both species continue to regenerate under shaded conditions. Under closed-canopy conditions, both species favor vegetative reproduction over sexual reproduction, thus intermediate and young trees are found under these conditions.
Environmental Description: This forest group is found in areas influenced by incursions of mild, wet, Pacific maritime air masses. Much of the annual precipitation occurs as rain, but where snow does occur, it can generally be melted by rain during warm winter storms. In the Cascades, it occurs on the upper east slopes in Washington, south of Lake Chelan and south to Mount Hood in Oregon. Elevations in the Cascades range from 610 to 1220 m (2000-4000 feet) in a very restricted range occupying less than 5% of the forested landscape in the East Cascades. In this region, these forests are associated with a submesic climate regime with annual precipitation ranging from 100 to 200 cm (40-80 inches) and maximum winter snowpacks that typically melt off in spring at lower elevations. Further east in the Northern Rockies, annual precipitation tends to be lower, averaging around 75 cm, while the elevation ranges from 550 m to over 1600 m (1700-5248 feet). Cooper et al. (1987) report that these interior hemlock-cedar forests require at least 20 cm of precipitation during the warm season. Occurrences generally are found on all slopes and aspects but grow best on sites with high soil moisture, such as toeslopes and bottomlands. At the periphery of its distribution, this group is confined to moist canyons and cooler, moister aspects. Generally these are moist, non-flooded or upland sites that are not saturated yearlong. This group differs from west of the Cascade groups in lower overall precipitation, warmer summer and colder winter temperatures, and more frequent fire (Goward and Spribille 2005).
Climate: This forest group is found in areas influenced by incursions of mild, wet, Pacific maritime air masses. Much of the annual precipitation occurs as rain, but where snow does occur, it can generally be melted by rain during warm winter storms. In the East Cascades, these forests are associated with a submesic climate regime with annual precipitation ranging from 100 to 200 cm (40-80 inches) and maximum winter snowpacks that typically melt off in spring at lower elevations. Further east in the Northern Rockies, annual precipitation tends to be lower, averaging around 75 cm. Cooper et al. (1987) report that these interior hemlock-cedar forests require at least 20 cm of precipitation during the warm season. Soil/substrate/hydrology: Parent materials are predominately sedimentary rock and argillite. Volcanic ash and loess deposits may have an influence on soil development, resulting in higher fertility and moisture-holding capacity required for supporting the dominant species. These forests occur on gravelly loams and silts with good aeration and drainage and a neutral to slightly acidic pH.
Climate: This forest group is found in areas influenced by incursions of mild, wet, Pacific maritime air masses. Much of the annual precipitation occurs as rain, but where snow does occur, it can generally be melted by rain during warm winter storms. In the East Cascades, these forests are associated with a submesic climate regime with annual precipitation ranging from 100 to 200 cm (40-80 inches) and maximum winter snowpacks that typically melt off in spring at lower elevations. Further east in the Northern Rockies, annual precipitation tends to be lower, averaging around 75 cm. Cooper et al. (1987) report that these interior hemlock-cedar forests require at least 20 cm of precipitation during the warm season. Soil/substrate/hydrology: Parent materials are predominately sedimentary rock and argillite. Volcanic ash and loess deposits may have an influence on soil development, resulting in higher fertility and moisture-holding capacity required for supporting the dominant species. These forests occur on gravelly loams and silts with good aeration and drainage and a neutral to slightly acidic pH.
Geographic Range: This forest group occurs in the interior regions of the Pacific Northwest, east of the Cascades; from interior British Columbia south to eastern Washington, Oregon, northern Idaho and western Montana east to the Continental Divide (DellaSala et al. 2011).
Nations: CA,US
States/Provinces: BC, ID, MT, OR, WA
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.836672
Confidence Level: Moderate
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.3 Western Hemlock - Grand Fir - Western Larch Mesic Lower Montane Forest Macrogroup | M500 | 1.B.2.Nb.3 |
| Group | 1.B.2.Nb.3.b Western Red-cedar - Western Hemlock Central Rocky Mountain Forest Group | G217 | 1.B.2.Nb.3.b |
| Alliance | A3612 Western Hemlock - Western Red-cedar Cool-Mesic Central Rocky Mountain Forest & Woodland Alliance | A3612 | 1.B.2.Nb.3.b |
| Alliance | A3613 Western Hemlock - Western Red-cedar Warm-Mesic Central Rocky Mountain Forest & Woodland Alliance | A3613 | 1.B.2.Nb.3.b |
Concept Lineage: No Data Available
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: >< Western Hemlock: 224 (Eyre 1980) [Moist western slopes of the northern Rocky Mountains, in northern ID, northwest MT, and northeast WA.]
>< Western Redcedar - Western Hemlock: 227 (Eyre 1980) [NW MT, N ID]
>< Western Redcedar: 228 (Eyre 1980)
>< Western Redcedar - Western Hemlock: 227 (Eyre 1980) [NW MT, N ID]
>< Western Redcedar: 228 (Eyre 1980)
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