North American boreal and western temperate forest vegetation

Salvador Rivas-Martínez, Daniel Sánchez-Mata & Manuel Costa

Itinera Geobotanica 12:5-316 (1999)


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Description of Plant Communities: Linnaeo americanae-Piceetea marianae

V. Linnaeo americanae-Piceetea marianae classis nova hoc loco

[Vaccinio-Piceetea sensu auct., non Br.-Bl., Sissingh & Vlieger in Prodr. Pflanzengesellschaften 6: 2. 1939 excl. Gaultherio-Piceetalia Br.-Bl., Sissingh & Vlieger in Prodr. Pflanzengesellschaften 6: 118. 1939 (art. 8), Tsugo-Thujetea plicatae Knapp in Geobot. Mitt. 4: 26. 1957 (art. 8), Alno-Aceretea macrophyllae Knapp in Geobot. Mitt. 4: 28. 1957 (art. 8), Pino-Abietetea lasiocarpae Knapp in Geobot. 4: 31. 1957 (art. 8), Abieto-Piceetea albae Knapp in Geobot. Mitt. 4: 55. 1957 (art. 8), Populetea balsamiferae Knapp in Geobot. Mitt. 4: 56. 1957 (art. 8), Pinetea latifoliae Knapp in Geobot. Mitt. 28: 8. 1964 (art. 8), Pseudotsugetea glaucae Knapp in Geobot. Mitt. 28: 8. 1964 (art. 8), Abieto-Piceetea glaucae Knapp 1957 ex Grandtner, Veget. Forest. Québec Mer.: 112. 1966 (art. 8)]

Typus nominis: Gaultherio-Piceetalia Br.-Bl., Sissingh & Vlieger ex Lavoie in Nat. Can. 95: 402. 1968.

North American Boreal and Temperate, sometimes Pluviseasonal Mediterranean, occasionally with submediterranean or steppic character, climactical (climatic and edaphic climax) coniferous micro- to megaforests. This vegetation class includes the related pyrogenic coniferous forests and their deciduous secondary forests and woodlands. We also include for the present the riparian forest cottonwood communities and tall tundra vegetation.

We assemble in this broad and rather heterogeneous class eight orders. The central three orders belong to coniferous forest communities: Gaultherio-Piceetalia: North American Boreal Region, Tsugetalia mertensiano-heterophyllae: North-Western Pacific Subregion and Pseudotsugo glaucae-Abietetalia bifoliae: Rocky Mountain Subregion. The order Ledo decumbentis-Betuletalia glandulosae includes the shrubby arctic, boreal and upper orotemperate tundra and open microforest tundra vegetation, distributed throughout the North American Arctic, North American Boreal and oro- and cryorotemperate Rocky Mountain territories. The rest of the orders include the deciduous secondary woodlands and the riparian cottonwood forests: Betulo papyriferae-Populetalia tremuloidis, represents the secondary woodlands in the North American Boreal Region and Rocky Mountain Subregion; Alno rubrae-Populetalia trichocarpae are secondary and also riparian forests in the North-Western Pacific Subregion; Populetalia angustifolio-deltoidis includes the cottonwood and riparian forests in the Rocky Mountain Subregion and North American Atlantic Region; and finally, the last order Populetalia fremontii, represents the Mediterranean riparian cottonwood forests in the Californian and Great Basin Regions, as well as the Desertic and Xeric Tropical deciduous riparian forests in the Madrean and Mexican Xerophytic Regions.

On the short synthesized table (table 1) we assemble 282 original relevés, from the territories of the North American Boreal and Rocky Mountain Regions, strictly pertaining to the coniferous orders Gaultherio-Piceetalia, Tsugetalia mertensiano-heterophyllae and Pseudotsugo-Abietetalia bifoliae.

Characteristic species: Actaea rubra subsp. arguta, Actaea rubra subsp. rubra, Amelanchier alnifolia var. alnifolia, Antennaria rosea, Aralia nudicaulis, Arceuthobium americanum, Arceuthobium campylopodum, Arceuthobium laricis, Arctostaphylos rubra, Arctostaphylos uva-ursi var. adenotricha, Arnica latifolia, Balsamorhiza sagittata, Calamagrostis rubescens, Calypso bulbosa var. occidentalis, Chimaphila umbellata subsp. occidentalis, Circaea alpina var. pacifica, Comandra umbellata subsp. pallida, Corallorhiza maculata, Corallorhiza striata, Corydalis aurea subsp. aurea, Disporum trachycarpum, Elymus trachycaulus subsp. subsecundus, Erythronium grandiflorum, Galium trifidum, Gaultheria hispidula, Geum macrophyllum, Goodyera oblongifolia, Hedysarum alpinum var. americanum, Hieracium albiflorum, Juniperus communis var. depressa, Juniperus communis var. montana, Juniperus horizontalis, Linnaea americana, Lonicera involucrata, Mahonia aquifolium, Maianthemum racemosum subsp. amplexicaule, Maianthemum stellatum, Mitella pentandra, Moehringia macrophylla, Osmorhiza berteroi, Osmorhiza depauperata, Paxistima myrsinites, Platanthera hyperborea, Platanthera orbiculata, Poa stenantha, Polemonium pulcherrimum subsp. pulcherrimum, Pterospora andromedea, Pyrola asarifolia, Ranunculus macounii, Ribes cynosbati, Rosa nutkana var. hispida, Rubus parviflorus, Salix discolor, Salix glauca var. glauca, Salix glauca var. villosa, Salix lutea, Salix prolixa, Salix scouleriana, Salix sitchensis, Shepherdia canadensis, Streptopus amplexifolius var. americanus, Streptopus amplexifolius var. chalazatus, Streptopus roseus var. roseus, Symphoricarpos albus var. albus, Thalictrum dasycarpum, Trientalis borealis subsp. latifolia, Vaccinium caespitosum, Valeriana sitchensis, Viola adunca var. adunca.

North American territorial characteristic species (also growing in Euro-Siberian Vaccinio-Piceetea abietis or in Sino-Japanese and Eastern Siberian Abietetea sachalinensio-mariesii, Rhytidio-Laricetea sibiricae, or Querco mongolicae-Betuletea davuricae geovicariant classes) Anemone parviflora, Arctostaphylos uva-ursi var. uva ursi, Boschniakia rossica, Calamagrostis purpurascens, Carex brunnescens subsp. brunnescens, Carex disperma, Cinna latifolia, Circaea alpina var. alpina, Coptis trifolia subsp. trifolia, Corallorhiza trifida, Cornus canadensis, Cystopteris montana, Diphasiastrum alpinum, Diphasiastrum complanatum, Diphasiastrum sitchense, Dryopteris expansa, Equisetum scirpoides, Equisetum sylvaticum, Equisetum variegatum subsp. variegatum, Galium boreale, Goodyera repens, Gymnocarpium dryopteris, Huperzia selago, Luzula parviflora subsp. melanocarpa, Lycopodium annotinum var. annotinum var. annotinum, Lycopodium annotinum var. pungens, Lycopodium dendroideum, Listera cordata, Maianthemum trifolium, Mitella nuda, Moehringia lateriflora, Moneses uniflora subsp. uniflora, Monotropa hypopithys, Monotropa uniflora, Orthilia secunda, Oxalis montana, Pedicularis labradorica, Pentaphylloides floribunda, Petasites frigidus var. frigidus, Phegopteris connectilis, Poa stenantha, Pulsatilla patens subsp. multifida, Pyrola chlorantha, Pyrola grandiflora, Pyrola minor, Rhododendron lapponicum, Rosa acicularis subsp. acicularis, Rubus arcticus subsp. arcticus, Salixalaxensis var.alaxensis, Salix bebbiana, Salix monticola, Stellaria calycantha, Thalictrum sparsiflorum, Trientalis europaea subsp. arctica, Viola selkirkii.

Other territorial characteristic species, which out of the forest or woodland communities belong to other phytosociological classes but also occurring in North America, are listed [Oxycocco-Sphagnetea Br.-Bl. & Tüxen ex Westhoff, Dijk & Passchier 1946 (vegetation communities of ombrogenic heighten temperate and boreal bogs), Loiseleurio-Vaccinietea Eggler ex Schubert 1960 [syn.: Loiseleurio-Cetrarietea Suzuki-Tokio & Umezu in Suzuki-Tokio 1964] (holarctic dwarf-shrubby, oro- and cryorotemperate, supra- and oroboreal and mesopolar windy snow-free heathlands communities), Salicetea herbaceae Br.-Bl. 1948 (snow-bed, oro- and cryoromediterranean, oro- and cryorotemperate, supra- and oroboreal, and mesopolar pygmy dwarf-shrubby and grassy holarctic communities)]: Andromeda polifolia (Oxycocco-Sphagnetea), Cassiope lycopodioides (Loiseleurio-Vaccinietea), Cassiope mertensiana (Loiseleurio-Vaccinietea), Cassiope tetragona var. saximontana (Loiseleurio-Vaccinietea) Cassiope tetragona var. tetragona (Loiseleurio-Vaccinietea), Chamaedaphne calyculata var. calyculata (Oxycocco-Sphagnetea), Chamaedaphne calyculata var. latifolia (Oxycocco-Sphagnetea), Empetrum nigrum subsp. hermaphroditum (Loiseleurio-Vaccinietea), Harimanella stelleriana (Salicetea herbaceae), Leptarrhena pyrolifolia (Salicetea herbaceae), Loiseleuria procumbens (Loiseleurio-Vaccinietea), Luetkea pectinata (Salicetea herbaceae), Phyllodoce caerulea (Loiseleurio-Vaccinietea), Phyllodoce empetriformis (Salicetea herbaceae), Phyllodoce glanduliflora (Loiseleurio-Vaccinietea), Phyllodoce xintermedia (Loiseleurio-Vaccinietea), Vaccinium oxycoccos (Oxycocco-Sphagnetea), Vaccinium uliginosum subsp. alpinum (Oxycocco-Sphagnetea), Vaccinium uliginosum subsp. microphyllum (Loiseleurio-Vaccinietea), Vaccinium vitis-idea subsp. minus (Loiseleurio-Vaccinietea).

Table 1
Linnaeo-Piceetea marianae coniferous forests
(Short synthesized syntaxa table)

Number of relevés 24 28 90 46 69 25 282
Alliance number 2 3 4 5 9 10 .
Ordinal number 1 2 3 4 5 6 7
Trees:
Abies balsamea V . . . . . I
Betula neoalaskana . III . . . . I
Thuja plicata . . V . . . I
Tsuga mertensiana . . . V . . I
Abies bifolia . . . . V . I
Pinus scopulorum . . . . I V II
Picea mariana V III . . . . II
Picea glauca IV V . . . . II
Tsuga heterophylla . . V II . . II
Pseudotsuga menziesii . . IV I . . II
Abies amabilis . . II III . . II
Pseudotsuga glauca . . I . V V III
Pinus latifolia . I . . V IV III
Picea engelmannii . . II III V I IV
Characteristic species:
Trientalis borealis IV . . . . . I
Coptis groenlandica IV . . . . . I
Maianthemum canadense V . . . . . I
Geocaulon lividum . V . . . . I
Arctagrostis arundinacea . V . . . . I
Polystichum munitum . . IV . . . I
Gaultheria shallon . . IV . . . I
Tiarella trifoliata . . IV . . . I
Rhododendron albiflorum . . . III . . I
Erythronium montanum . . . IV . . I
Moneses uniflora . . . . III . I
Aster conspicuus . . . . III . I
Symphoricarpos oreophilus . . . . . IV I
Juniperus scopulorum . . . . . IV I
Mertensia paniculata II V . . . . II
Trillium ovatum . . IV II . . II
Clintonia uniflora . . IV IV . . II
Oplopanax horridus . . V II . . II
Rubus pedatus . . IV V . . II
Ribes montigenum . . . . III II II
Mahonia repens . . . . IV IV II
Juniperus depressa . . . . V IV II
Paxistima myrsinites . . III . IV II III
Vaccinium scoparium . . . III IV II III
Maianthemum stellatum . . V II I II IV
Goodyera oblongifolia . . V II III IV IV
Pyrola asarifolia . I III II IV II V
Orthilia secunda II IV V V IV II V
Linnaea americana V V IV V V IV V
Cornus canadensis V V IV V III I V

Alliances: 1. [2] Gaultherio-Piceion glaucae and Piceion rubentis (Gaultherio-Piceetalia). 2. [3] Ledo-Piceion marianae (Gaultherio-Piceetalia). 3. [4] Tsugion heterophyllae (Tsugetalia mertensiano-heterophyllae). 4. [5] Tsugion mertensianae (Tsugetalia mertensiano-heterophyllae). 5. [9] Piceo-Abietion bifoliae (Pseudotsugo-Abietetalia bifoliae). 6. [10] Pino-Pseudotsugion glaucae (Pseudotsugo-Abietetalia bifoliae). 7. Synthesized table.

Syntaxa Ic Io Itc Tp Ts Tmin m Mb
Linnaeo-Piceetea marianae 5-46 0.3-40.0 < 520 180-2800 170-1000 < 14 < 9 Po,Bo,
Te,Me,Tr
Va. Gaultherio-Piceetalia 20-46 1.8-20.0 - 380-1050 300-600 < -4 < -14 Bo, Te
Vb. Tsugetalia mert.-heteroph. 5-23 3.6-40.0 < 280 380-1400 270-550 < 8 < 5 Te, Bo, Me
Vc. Alno rub.-Populetalia trich. 5-25 4.8-40.0 < 250 400-1400 280-550 < 8 < 5 Te, Bo, Me
Vd. Pseudotsugo g.-Abietetalia b. 21-34 2.0-9.0 - 380-1300 270-650 < -3 < -7 Te, Me
Ve. Betulo p.-Populetalia tremul. 21-46 1.8-22.0 - 380-1200 280-700 < 0 < -2 Te, Bo, Me
Vf. Populetalia angust.-deltoidis 17-38 2.0-10.0 < 470 740-2500 450-900 < 12 < 7 Te, Me
Vg. Populetalia fremontii 6-28 0.3-3.6 200-520 1200-2800 500-1000 < 14 < 9 Me, Tr
Vh. Ledo dec.-Betuletalia gland. 10-40 2.8-30.0 - 180-700 170-400 < 0 < -2 Bo, Po, Te

Figure 9. Synopsis of the bioclimatic diagnoses of syntaxa belonging to Linnaeo-Piceetea marianae. Relationships between the natural potential vegetation forests and the thresholds of the bioclimatic indexes and climatic parameter values [Va. Gaultherio-Piceetalia, Vb. Tsugetalia mertensiano-heterophyllae, Vc. Alno rubrae-Populetalia trichocarpae, Vd. Pseudotsugo glaucae-Abietetalia bifoliae, Ve. Betulo papyriferae-Populetalia tremuloidis, Vf. Populetalia angustifolio-deltoidis, Vg. Populetalia fremontii, Vh. Ledo decumbentis-Betuletalia glandulosae]. Ic: Continentality Index, Io: Ombrothermic Index, Itc: Compensated Thermicity Index, Tp: Yearly Positive Temperature Index, Tps: Positive Summer Temperature, Tmin: Average temperature value of the coldest month of the year, m: Average minimum temperature of the coldest month of the year (Tmin and m in degrees Celsius), Mb: Macrobioclimate (Bo: Boreal, Te: Temperate, Me: Mediterranean, Tr: Tropical, Po: polar).

North American associations of North American biogeographic sectors
Linnaeo americanae-Piceetea marianae 1 2.1 2.2 3 4.1 4.2 4.3 4.4 6 5 7 8
Va. Gaultherio-Piceetalia . + + + . . . . . . . .
Vb. Tsugetalia mertensiano-heterophyllae . . . . + + + . . . . .
Vc. Alno rubrae-Populetalia trichocarpae . . + . + + + . . + . .
Vd. Pseudotsugo glaucae-Abietetalia bifoliae . . . . . . + + + . . .
Ve. Betulo papyriferae-Populetalia tremuloidis . + + + . . + + + + . .
Vf. Populetalia angustifolio-deltoidis . . . . . . + + + . . .
Vg. Populetalia fremontii . . . . . . . . + + + +
Vh. Ledo decumbentis-Betuletalia glandulosae + + + + + + + + . . . .

Figure 10. Relationships between biogeographic provinces and regions of North America and the orders of Linnaeo-Piceetea marianae (Va. Gaulterio-Piceetalia, Vb. Tsugetalia mertensiano-heterophyllae, Vc. Alno rubrae-Populetalia trichocarpae, Vd. Pseudotsugo glaucae-Abietetalia bifoliae, Ve. Betulo papyriferae-Populetalia tremuloidis, Vf. Populetalia angustifolio-deltoidis, Vg. Populetalia fremontii, Vh. Ledo decumbentis-Betuletalia glandulosae): 1. Circumarctic Region. 2.1. Canadian Boreal Province. 2.2. Yukonian-Alaskan Province. 3. North American Atlantic Region. 4.1. Boreal Oceanic Alaskan Province. 4.2. Cascade Province 4.3. Northern Rocky Mountain Province. 4.4. Central-Eastern Rocky Mountain Province. 6. Great Basin Region. 5. Californian Region. 7. Mexican Xerophytic Region. 8. Madrean Region.

Key to identify the coniferous forest associations

We publish here a bioclimatic, biogeographic and floristic dichotomous key for the identification of the climactical and permanent coniferous forest associations of the North American Boreal and Rocky Mountain Regions, also incluing the orotemperate (subalpine) and hemiboreal territories of the North American Atlantic Region, belonging to the orders: Gaultherio-Piceetalia, Tsugetalia mertensiano-heterophyllae and Pseudotsugo glaucae-Abietetalia bifoliae. The key uses several geographic, biogeographic, bioclimatic, ecologic and floristic features of the studied territory and permit us to know the particular phytosociological unit.

1 Oceanic or hyperoceanic territories: Ic < 21 (exceptionally barely subcontinental Ic<23) 2
Continental territories: Ic > 21 19
2 Territories south of 45ºN (Pacific North America) 3
Territories north of 45ºN (Pacific North America) and north or south of 45ºN (rest of North America) 4
3 3. Oceanic Temperate and Hyperoceanic Temperate bioclimates: Iosc4 > 2.0 (Tsugetalia mertensiano-heterophyllae) [see remark (1)] 4
3. Pluviseasonal Mediterranean bioclimate: Io > 2.0, Iosc4 <= 2.0, Itc < 200, or when Itc 200-250, then Io > 4.5[see remarks (2) and (3)] Calocedro-Pinetea jeffreyi
4 Oceanic Boreal bioclimate: at < 200 m, Tp < 720, in SW coast of Alaska (Boreal Oceanic Alaskan Province) 5
Oceanic Temperate or Hyperoceanic Temperate bioclimates: at < 200 m, Tp > 720 (Cascade Province) 7
5 Boreal Oceanic Alaskan Province territories. Coastal granitic permanent micro-mesoforests of Pinus contorta as dominant tree in the canopy with Juniperus depressa and Amelanchier semiintegrifolia in the understory (Boreal Oceanic-Eastern Alaskan Sector) 6b. Junipero depressae-Pinetum contortae
Climactical meso- and macroforests with Tsuga mertensiana, Tsuga heterophylla or Picea sitchensis as dominant coniferous trees in the canopy 6
6 Upper mesoboreal and supraboreal territories (Tp 380-570) with Tsuga mertensiana (Boreal Oceanic Alaskan Province) 5d. Tsugo mertensianae-Piceetum sitchensis
Lower mesoboreal and upper thermoboreal territories (Tp 570-720) without Tsuga mertensiana with Tsuga heterophylla (Boreal Oceanic Alaskan Province) 4c. Rubo stellati-Piceetum sitchensis
7 Cascade Province territories. Coastal sandy or hard rocky steep permanent micro-mesoforests of Pinus contorta as dominant tree but usually with Picea sitchensis or Pinus muricata in the canopy and Lonicera ledebourii and Myrica californica in the understory (coasts areas of Cascade Province) 6a. Lonicero ledebourii-Pinetum contortae
Climactical coniferous meso-, macro- or megaforests organized in the canopy by Abies amabilis, Abies grandis, Abies lasiocarpa, Abies procera, Picea sitchensis, Pseudotsuga menziesii, Sequoia sempervirens, Thuja plicata, Tsuga heterophylla or Tsuga mertensiana (Cascade Province) 8
8 Territories from upper mesotemperate to lower orotemperate thermotypes (Tp > 600, Itc < 250) with Abies grandis, Picea sitchensis, Pseudotsuga menziesii, Sequoia sempervirens, Thuja plicata or Tsuga heterophylla 9
Upper orotemperate territories (Tp < 600) with Abies lasiocarpa or Abies procera and Tsuga mertensiana 15
9 Hyperoceanic areas, Ic < 11.0 (Oregonian-Vancouverian Coastal Sector) 10
Euoceanic to semicontinental areas (exceptionally barely subcontinental) Ic 11-23 11
10 Mesotemperate territories (Itc > 200), average temperature of the coldest month Tmin > 5.0, megaforests with Sequoia sempervirens (south of Oregonian Coastal Subsector) 4d. Tsugo heterophyllae-Sequoietum sempervirentis
Upper mesotemperate and lower supratemperate territories (Itc > 120), average temperature of the coldest month Tmin > 4.0, megaforests with Picea sitchensis but without Sequoia sempervirens (Oregonian-Vancouverian Coastal Sector) 4a. Vaccinio ovati-Piceetum sitchensis
11 Abies amabilis and Tsuga heterophylla as dominant trees in the forest canopy 12
Without Abies amabilis in the forest canopy 13
12 Pseudotsuga menziesii in the forest canopy and Achlys triphylla, Vaccinium ovalifolium, or Rubus lasiococcus in the understory (Cascade Ranges Sector, Canadian Coastal Mountains Sector   4g. Abieti amabilis-Tsugetum heterophyllae
Without these plants but with Picea sitchensis and Pinus contorta in the neighboring permanent microforest communities (Canadian Coastal Mountains Sector) 4b. Abieti amabilis-Piceetum sitchensis
13 Pseudotsuga glauca in the forest canopy and Aralia nudicaulis in the understory (Columbia Mountains Sector) 4h. Piceo engelmannii-Tsugetum heterophyllae
Without those plants in the forest 14
14 With dominance of Abies grandis and sometimes the presence Picea engelmannii in the forest canopy, but without Polystichum munitum, Tiarella trifoliata or Gaultheria shallon in the understory, semicontinental areas (Ic > 18) of the Cascade Ranges Sector 4f. Abieti grandis-Pseudotsugetum menziesii
Without dominance of Abies grandis or the presence of Picea engelmannii in the forest canopy, but with Polystichum munitum, Tiarella trifoliata or Gaultheria shallon in the understory, euoceanic areas (Ic < 18) of the Oregonian-Vancouverian Coastal and Cascade Ranges Sectors 4e. Gaultherio shallonis-Pseudotsugetum menziesii
15 With Abies amabilis but without Abies lasiocarpa in the forest canopy 16
With Abies lasiocarpa but without Abies amabilis in the forest canopy 17
16 Abies procera or Picea engelmannii in the forest canopy (Cascade Ranges Sector) 5c. Tsugo mertensianae-Abietetum procerae
Without Abies procera or Picea engelmannii in the forest canopy, but often with Elliottia pyroliflorus and Menziesia ferruginea in the understory (Vancouverian Subsector and Canadian Coastal Mountains Sector) 5a. Abieti amabilis-Tsugetum mertensianae
17 Pinus albicaulis or Larix lyallii in the forest canopy 18
Without those trees, but with Picea engelmannii in the forest canopy and Rhododendron albiflorum in the understory (Olympic Mountains Subsector, Cascade Ranges and Columbia Mountains Sectors) 5b. Abieti lasiocarpae-Tsugetum mertensianae
18 Pinus albicaulis in the forest canopy (Cascade Ranges Sector) 5e. Abieti lasiocarpae-Pinetum albicaulis
Larix lyallii in the forest canopy (Washingtonian Cascade Subsector and Columbia Mountains Sector) 5f. Phyllodoco glanduliflorae-Laricetum lyallii
19 Picea mariana or Picea glauca in the forest canopy, but without Picea engelmannii, Picea albertiana, Pseudotsuga glauca or Abies bifolia in the canopy (North American Boreal Region and in the hemiboreal or subalpine adjacent territories of the North American Atlantic Region) 20
Without Picea mariana or Picea glauca but with Picea engelmannii, Picea albertiana, Pseudotsuga glauca or Abies bifolia (Rocky Mountain Subregion) 30
20 Boreal and North American Atlantic Region adjacent territories, Picea mariana or Picea glauca with Abies balsamea in the canopy, with or without Pinus banksiana in the canopy, east to 120ºW (Canadian Boreal Province and Appalachian, Great Lakes and Canadian Prairies Sectors) 21
Picea glauca or Picea mariana in the forest canopy, but without Abies balsamea or Pinus banksiana, west to 120ºW 27
21 Pinus banksiana dominant tree in the forest canopy, shallow or gravelly soils and fire resistant forests 22
Without Pinus banksiana in the forest canopy 23
22 Kalmia angustifolia or Comptonia peregrina in the forest understory, east of 100ºW (Eastern Canadian Boreal Sector) 1a. Pinetum banksianae
Without Kalmia angustifolia or Comptonia peregrina in the forest understory, west of 100ºW (Western Canadian Boreal Sector) 1c. Oryzopsio asperifoliae-Pinetum banksianae
23 Picea rubens in the forest canopy (Appalachian Sector Eastern Great Lakes Subsector) 2e. Abieti balsameae-Piceetum rubentis
Without Picea rubens in the forest canopy (Canadian Boreal Province and hemiboreal or subalpine territories of the North American Atlantic Region) 24
24 Vaccinium oxycoccos and Chamaedaphne latifolia in the forest understory and often Larix laricina in the canopy, boggy soils (Canadian Boreal Province, Appalachian and Great Lakes sectors) 2c. Sphagno-Piceetum marianae
Without Vaccinium oxycoccos and Chamaedaphne latifolia in the forest understory and rarely Larix laricina in the canopy, not in boggy soils 25
25 With Kalmia angustifolia or Vaccinium angustifolium and without Mertensia paniculata in the forest understory, east to 95ºW 26
Without Kalmia angustifolia or Vaccinium angustifolium, but with Mertensia paniculata in the forest understory, west to 95ºW (Western Canadian Boreal and Canadian Prairies Sectors, and Western Hemiboreal Great Lakes Subsector) 2d. Mertensio paniculatae-Abietetum balsameae
26 Clintonia borealis or Coptis groenlandica in the forest understory, thermoboreal areas (Newfoundlandian Sector, Eastern Canadian Boreal Sector) 2a. Abietetum balsameae
Without Clintonia borealis, Maianthemum canadense or Coptis groenlandica in the forest understory, meso- and supraboreal areas (Newfoundlandian Sector, Eastern Canadian Boreal Sector) 2b. Kalmio angustifoliae-Piceetum marianae
27 Yukonian-Alaskan Province territories. Pinus latifolia in the canopy, north of 57ºN (Cassiar Mountains Subsector) 3d. Pulsatillo multifidae-Pinetum latifoliae
Without Pinus latifolia but with Picea mariana, Picea glauca or Larix laricina in the forest canopy (Yukonian-Alaskan Province) 28
28 Carex lugens or Vaccinium oxycoccos in the forest understory, boggy soils (Yukonian-Alaskan Province and locally in Fraser Interior Plateau and Canadian Rockies Sectors) 3a. Rubo chamaemori-Piceetum marianae
Without Carex lugens or Vaccinium oxycoccos in the forest understory, not in boggy soils 29
29 Picea mariana and Picea glauca in the canopy and Rubus chamaemorus and Equisetum sylvaticum in the forest understory, meso- and supraboreal continental subhumid to humid localities with vadose horizon (Yukonian-Alaskan Province) 3b. Piceetum glauco-marianae
Picea glauca as more frequent tree than Picea mariana, Rubus chamaemorus or Equisetum sylvaticum but with Picea glauca and Shepherdia canadensis, meso- and supraboreal xeric, dry to lower subhumid localities without vadose horizon (Yukonian-Alaskan Province) 3c. Hypno procerrimi-Piceetum glaucae
30 Rocky Mountain Subregion territories and adjacent high mountains areas of the Great Basin Region. Orotemperate areas (Tp < 800), with Abies bifolia or Picea engelmannii in the forest canopy 31
Supratemperate territories (Tp > 800), without Abies bifolia or Picea engelmannii but with Pinus scopulorum or Juniperus scopulorum in the forest canopy 40
31 Northern Rocky Mountain Province territories (31 to 35). Upper orotemperate areas (Tp < 500), with Empetrum hermaphroditum, Betula glanduliflora or Arctostaphylos rubra in the forest understory, but without Picea albertiana, Populus tremuloides or Pseudotsuga glauca in the canopy (Canadian Rockies Sector) 9d. Empetro hermaprhoditi-Abietetum bifoliae
Without Empetrum hermaphroditum, Betula glanduliflora or Arctostaphylos rubra in the forest understory 32
32 Picea albertiana and occasionally Picea glauca in the forest canopy and Ribes lacustre or Viburnum edule in the understory (Canadian Rockies Sector and Fraser Interior Plateau Sector) 9e. Pinetum engelmannio-albertianae
Without Picea albertiana and Picea glauca or Ribes lacustre or Viburnum edule in the forest understory 33
33 Pinus latifolia as dominant tree in the forest canopy, but Picea albertiana, Picea engelmannii, Abies bifolia or Pseudotsuga menziesii var. glauca as small trees growing in the undercanopy, and Vaccinium scoparium, Cornus canadensis or Ledum groenlandicum in the understory (Rocky Mountain Subregion) 9h. Vaccinio scoparii-Pinetum latifoliae
Without Pinus latifolia as the only or dominant tree in the forest canopy 34
34 Menziesia ferruginea and Viola orbiculata in the forest understory (Northern Rocky Mountain Province) 9c. Menziesio ferrugineae-Abietetum bifoliae
Without these plants in the forest understory 35
35 With Larix occidentalis in the forest canopy and Maianthemum stellatum or Symphoricarpos albus in the understory, upper supra- and lower orotemperate territories: Tp 700-1300 (Northern Rocky Mountain Province 10a. Larici occidentalis-Pseudotsugetum glaucae
Without these plants 36
36 Central-Eastern Rocky Mountain Province (36 to 38). Pinus aristata in the forest canopy, upper orotemperate areas (Tp 380-600), Colorado Rockies Sector 9g. Penstemono whippleani-Pinetum aristatae
Without Pinus aristata in the forest canopy 37
37 Pinus albicaulis in the forest canopy, upper orotemperate territories (Tp 380-600), Northern Rocky Mountains Province 9i. Vaccinio scoparii-Pinetum albicaulis
Without Pinus albicaulis in the forest canopy 38
38 Picea pungens in the forest canopy, lower orotemperate territories (Tp 550-800), Utah Rockies and Colorado Rockies Sector 9f. Piceetum pungentis
Without Picea pungens but with Picea engelmannii and Pinus flexilis in the forest canopy 39
39 With Arctostaphylos patula and without Vaccinium scoparium in the forest understory, orotemperate submediterranean areas (Tp 450-800), Wheeler Peak National Park, Upper Nevada Basin Sector 9b. Arctostaphylo patulae-Pinetum flexilis
Without Arctostaphylos patula and with Vaccinium scoparium in the forest understory, orotemperate territories (Tp 400-800), Central-Eastern Rocky Mountain Province 9a. Vaccinio scoparii-Abietetum bifoliae
40 Rocky Mountain Subregion (39 to 40). Supratemperate (Tp > 800) and submediterranean (Ios2 < 2.5) or Pluviseasonal Continental Mediterranean (Iosc4 < 2.0) territories, in shallow soils and steep slopes with Pinus flexilis in the forest canopy (Central-Eastern Rocky Mountain Province) 10d. Pseudotsugo glaucae-Pinetum flexilis
Without Pinus flexilis in the forest canopy 41
41 Pseudotsuga glauca as dominant tree in the forest canopy and Shepherdia canadensis in the understory (Rocky Mountain Subregion) 10b. Shepherdio canadensis-Pseudotsugetum glaucae
Pinus scopulorum as dominant tree in the forest canopy and Rhus trilobata in the understory but without Shepherdia canadensis (High Plains Rockies Sector) 10c. Rhoo trilobatae-Pinetum scopulorum

Key comments:

(1) The coniferous characteristic species which organize the canopy of Tsugetalia mertensiano-heterophyllae forest communities are: Abies amabilis, Abies lasiocarpa, Abies procera, Chamaecyparis nootkatensis, Picea sitchensis, Pinus contorta var. contorta, Taxus brevifolia, Thuja plicata, Tsuga heterophylla, Tsuga mertensiana, and partially: Pseudotsuga menziesii var. menziesii and Sequoia sempervirens.

(2) If Ic < 21, Io 1.0-4.5, Iosc4 <= 2.0, Itc 200-480, the woodlands are organized by evergreen or deciduous tree oaks or scrubby evergreen oaks ("encinares" and "chaparrales") belonging to Heteromelo-Quercetea agrifoliae class [see Itinera Geobot. 10: 16-53. 1997]. The trees and more frequent big shrubs are: Aesculus californica, Aesculus parryi, Ceanothus jepsonii subsp. albiflorus, Cercocarpus montanus var. glaber, Cercocarpus montanus var. minutiflorus, Cupressus macnabiana, Cupressus sargentii, Fraxinus dipetala, Fremontodendron californicum, Garrya buxifolia, Garrya elliptica, Heteromeles arbutifolia, Juniperus californica, Malosma laurina, Ornithostaphylos oppositifolia, Pinus quadrifolia, Pinus sabiniana, Prunus ilicifolia, Rhus integrifolia, Rhus ovata, Quercus agrifolia, Quercus douglasii, Quercus durata, Quercus engelmannii, Quercus lobata, Quercus tomentella, Quercus wislizenii and Xylococcus bicolor.

(3) If Ic <= 21, Iosc4 <= 2.0, Itc < 250, Tp 400-1700, Io > 2.0, or when Itc 200-250 then Io > 4.5, the climactical natural potential vegetation is the coniferous and mixed evergreen or broad-leaved deciduous forests living in (meso-), supra- or oromediterranean pluviseasonal oceanic and hyperoceanic, dry to hyperhumid bioclimates of the Californian Region. [see: Itinera Geobot. 10: 54-90. 1997]. The coniferous characteristic species which organized the forest canopy are: Abies bracteata, Abies lowiana, Abies magnifica, Calocedrus decurrens, Juniperus occidentalis var. australis, Pinus jeffreyi, Pinus lambertiana, Pinus washoensis, Pseudotsuga macrocarpa, Sequoiadendron giganteum, Torreya californica and partially (because they can be also present in the Tsugetalia mertensiano-heterophyllae forest communities): Abies shastensis, Pinus contorta var. murrayana, Pinus ponderosa var. ponderosa, Pseudotsuga menziesii var. menziesii and Sequoia sempervirens.