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: Tsugetalia mertensiano-heterophyllae

 Vb. Tsugetalia mertensiano-heterophyllae ordo novus hoc loco

[Tsugo-Thujetalia plicatae Knapp in Geobot Mitt. 4: 27. 1957 (art. 7, 8), Abietetalia procerae Knapp in Geobot Mitt. 4: 31. 1957 (art. 8), Abieti-Tsugetalia mertensianae Knapp in Geobot Mitt. 4: 31. 1957 (art. 8), Vaccinietalia membranacei Brooke, Peterson & Krajina in Ecol. Western North. Am. 2(2) 261. 1970 (art. 9, 29), Tsugetalia plicatae Brooke, Peterson & Krajina in Ecol. Western North. Am. 2(2): 271. 1970 (art. 8)]

Typus nominis: Tsugion heterophyllae alliancia nova hoc loco.

North American climactical and permanent edaphophilous coniferous forests of the North-Western Pacific Subregion (Rocky Mountain Region), mainly spreading mostly into Oceanic Temperate bioclimate territories (included the Submediterranean bioclimatic variant), but also in certain areas with other bioclimates like Hyperoceanic Temperate, Pluviseasonal Oceanic Mediterranean and Oceanic Boreal. According to the ombrothermic conditions, their timberlands should be macro- and megaforests but in very cold territories or poor soils, also can be micro- and mesoforests. They are distributed throughout the mesotemperate to orotemperate or hemiboreal subhumid to ultrahyperhumid, as well as and in meso- or supraboreal humid to ultrahyperhumid territories. Locally these forest communities can also develop in meso- and supramediterranean subhumid to humid bioclimatic belt areas. These forests grow in all kind of substrata but mostly on cambisols, luvisols, andosols, regosols and podzols. In spite of their major biodiversity occurs throughout the Cascade Province territories, these forests are also common in the Boreal Oceanic Alaskan Province areas (with the exception of Aleutian Islands and Alaska Peninsula Subsectors where coniferous forests are absent). Finally, as micro- or mesoforest permanent communities, could be recognized in dry coastal slopes and sand dunes (Pinion contortae) from Haines (Alaska) to Mendocino (California).

Bioclimatic diagnosis: Ic 5-23, Io 3.6-40.0, Itc < 270, Tp 380-1400, Tps 270-550, Tmin < 8º, m < 5º. [Booc, Bosc, Teho, Teoc, Teco, Mepo-Tbo, Mbo, Sbo, Mte, Ste, Ote, Mme, Sme-Shu, Hum, Hhu, Uhh].

Within the order Tsugetalia mertensiano-heterophyllae we recognize three alliances with different ecological requirements: 4. Tsugion heterophyllae: Cascade and Boreal Oceanic Alaskan Provinces; mesoboreal, hemiboreal, meso-, supra- and lower orotemperate and meso- and supramediterranean; subhumid to ultrahyperhumid, 5. Tsugion mertensianae: Cascade and Boreal Oceanic Alaskan Provinces; supraboreal and upper mesoboreal, upper orotemperate; humid to ultrahyperhumid, 6. Pinion contortae: North Western Pacific Subregion coastal territories in the Boreal Eastern Alaskan Sector (Haines-Juneau Subsector), and coastal areas of the Canadian Coastal Mountains as well as from the Oregonian-Vancouverian Coastal territories to Northern Californian Coastal Sector (mesoboreal, hemiboreal, supra- and mesotemperate and upper mesomediterranean).

In a short synthesized synoptical table (table 14) we assemble 136 relevés from North-Western Pacific Subregion belonging to Tsugion heterophyllae and Tsugion mertensianae alliances. A synopsis of the bioclimatic diagnoses of the alliances and associations which we recognize in the Tsugetalia mertensiano-heterophyllae order is also given in figure 19.

Table 14
5. Tsugion heterophyllae
and 6. Tsugion mertensianae
(Short synthesized table syntaxa)

Number of species (average) 28 27 25 34 30 31 26 32 24 21 24 23 26
Number of relevés 5 5 16 7 20 14 14 8 13 12 15 6 136
Association number 5c 5b 5a 5d 5e 5f 5g 5h 6c 6a 6b 6d .
Ordinal number 1 2 3 4 5 6 7 8 9 10 11 12 13
Trees:
Sequoia sempervirens . . . V . . . . . . . . I
Abies grandis . . . .   V . . II . . . I
Pseudotsuga glauca . . . . . . . IV . . . . I
Abies procera . . . . . . . . V . . . I
Abies lasiocarpa . . . . . . . I . . V . I
Pseudotsuga menziesii . . III IV V V IV . IV . . . III
Thuja plicata . V IV II V III IV V . . . . IV
Tsuga heterophylla V V V V V IV V V III . . I IV
Chamaecyparis nootkatensis . . . . . . I . . IV I . II
Tsuga mertensiana . . . . . . . . V V V IV II
Abies amabilis . V . .   . V . III V . . II
Picea sitchensis V V V III . . . . . . . V III
Picea engelmannii . . . . . II I V IV . IV . III
Characteristic species:
Rubus stellatus V . . . . . . . . . . . I
Coptis aspleniifolia . III . . . . . . . . . . I
Vaccinium ovatum . . V V .   . . . . . . I
Viola sempervirens . . . III I . . . . . . . I
Chrysolepis minor . . . . I III . . . . . . I
Aralia nudicaulis . . . . . . . IV . . . . I
Elliottia pyroliflorus . . . . . . . . . III . . I
Rubus chamaemorus . . . . . . . . . . . V I
Vancouveria hexandra . . . V II I I . . . . . II
Asarum caudatum . . . IV II I I II . . . . III
Polystichum munitum . I V V V . I . . . . . III
Gaultheria shallon . I V IV V . III . . . . . III
Tiarella trifoliata V V III . III . III . . . . . III
Vaccinium parvifolium . I IV I V I III . . . . . III
Galium triflorum . IV IV IV IV IV II IV . . . . IV
Rhododendron albiflorum . . . . . . . . . III V . I
Erythronium montanum . . . . . . . . I II II . II
Rubus lasiococcus . . . . . II III . IV V IV . III
Achlys triphylla . . . . V IV IV . IV I I . III
Pyrola asarifolia . . . . II II III IV I . . III III
Trillium ovatum . . III V IV III II . III I . . IV
Tiarella unifoliata . . . . III II III V III IV IV . IV
Maianthemum stellatum . IV I II IV IV IV II II . . . IV
Clintonia uniflora . III . I III IV IV V V I II . V
Goodyera oblongifolia I I . I III V III V III . I . V
Linnaea americana . III . . V V V V III I I III V
Vaccinium ovalifolium V . III I . I IV II III V III IV V
Oplopanax horridus V IV I . I I III III . . I IV V
Rubus pedatus V I I . . . III I I V III III V
Vaccinium membranaceum III V . . I III IV IV IV V V . V
Cornus canadensis V V . . I II V IV III II I V V
Orthilia secunda III I . I I III IV III V IV IV IV V
Menziesia ferruginea V V III III I . III III I V I III V

Associations: 1. [5c] Rubo stellati-Piceetum sitchensis (Tsugion heterophyllae). 2. [5b] Abieti amabilis-Piceetum sitchensis (Tsugion heterophyllae). 3. [5a] Vaccinio ovati-Piceetum sitchensis (Tsugion heterophyllae). 4. [5d] Tsugo heterophyllae-Sequoietum sempervirentis (Tsugion heterophyllae). 5. [5e] Gaultherio shallonis-Pseudotsugetum menziesii (Tsugion heterophyllae). 6. [5f] Abieti grandis-Pseudotsugetum menziesii (Tsugion heterophyllae). 7. [5g] Abieti amabilis-Tsugetum heterophyllae (Tsugion heterophyllae). 8. [5h] Piceo engelmannii-Tsugetum heterophyllae (Tsugion heterophyllae). 9. [6c] Tsugo mertensianae-Abietetum procerae (Tsugion mertensianae). 10. [6a] Abieti amabilis-Tsugetum mertensianae (Tsugion mertensianae). 11. [6b] Abieti lasiocarpae-Tsugetum mertensianae (Tsugion mertensianae). 12. [6d] Tsugo mertensianae-Piceetum sitchensis (Tsugion mertensianae). 13. Synthesized table.

Syntaxa Ic Io Itc Tp Ts Tmin m Mb, Var
Vb. Tsugetalia merten.-heteroph. 5-23 3.6-40.0 < 280 380-1400 270-550 < 8 < 5 Te, Bo, Me
5. Tsugion heterophyllae 5-23 3.6-30.0 < 270 570-1400 350-550 < 8 < 5 Te, Bo
5a. Vaccinio ov.-Piceetum sitchensis 6-12 11.0-28.0 120-260 1000-1400 380-500 > 4 > 2 Te, Sbm
5b. Abieti amab.-Piceetum sitchensis 11-18 12.0-30.0 - 720-1000 380-430 < 4 < 2 Te
5c. Rubo stellat.-Piceetum sitchensis 14-21 10.0-40.0 - 570-720 370-420 < -1 < -2 Bo
5d. Tsugo h-Sequoietum sempervir. 5-7 7.0-14.0 200-270 1200-1400 350-450 > 5 > 2 Te, Sbm
5e. Gaultherio s.-Pseudotsugetum m. 11-18 5.6-12.0 < 210 600-1400 380-550 < 5 < 2 Te, Sbm
5f. Abieti g.-Pseudotsugetum menz. 18-22 3.6-9.0 - 600-1050 380-550 < -4 < -9 Te, Sbm
5g. Abieti am.-Tsugetum heterophyll. 12-21 8.0-18.0 - 600-1000 370-500 < 0 < -2 Te
5h. Piceo eng.-Tsugetum heterophyl. 18-23 7.0-12.0 - 600-800 380-500 < -6 < -12 Te
6. Tsugion mertensianae 11-23 9.0-30.0 - 380-650 270-400 < -3 < -5 Te, Bo
6a. Abieti am.-Tsugetum mertensian. 11-16 12.0-28.0 - 380-600 280-370 < -3 < -5 Te
6b. Abieti las.-Tsugetum mertensian. 16-23 9.0-18.0 - 380-600 280-380 < -4 < -7 Te
6c. Tsugo mert.-Abietetum procerae 16-21 9.0-18.0 - 450-650 300-400 < -3 < -5 Te
6d. Tsugo mert.-Piceetum sitchensis 14-23 9.0-30.0 - 380-570 280-380 < -5 < -9 Bo
6e. Abieti lasioc.-Pinetum albicaulis 16-23 9.0-18.0 - 380-500 280-360 < -5 < -10 Te
6f. Phyllodoco gl.-Laricetum lyallii 18-23 9.0-14.0 - 380-500 270-350 < -7 < -14 Te
7. Pinion contortae 5-21 6.0-24.0 < 280 670-1400 370-480 < 8 < 4 Te, Bo, Me
7a. Lonicero led.-Pinetum contortae 5-11 6.0-18.0 180-280 1000-1400 390-480 < 8 < 4 Te, Me
7b. Junipero dep.-Pinetum contortae 11-21 10.0-24.0 < 120 670-900 370-420 < 3 < -1 Bo, Te

Figure 19. Synopsis of the bioclimatic diagnoses of syntaxa belonging to Tsugetalia mertensiano-heterophyllae order. Relationships between the potential natural vegetation forests and the thresholds of the bioclimatic indexes and climatic parameter values [5. Tsugion heterophyllae (5a. Vaccinio ovati-Piceetum sitchensis, 5b. Abieti amabilis-Piceetum sitchensis, 5c. Rubo stellati-Piceetum sitchensis, 5d. Tsugo heterophyllae-Sequoietum sempervirentis, 5e. Gaultherio shallonis-Pseudotsugetum menziesii, 5f. Abieti grandis-Pseudotsugetum menziesii, 5g. Abieti amabilis-Tsugetum heterophyllae, 5h. Piceo engelmannii-Tsugetum heterophyllae), 6. Tsugion mertensianae (6a. Abieti amabilis-Tsugetum mertensianae, 6b. Abieti lasiocarpae-Tsugetum mertensianae, 6c. Tsugo mertensianae-Abietetum procerae, 6d. Tsugo mertensianae-Piceetum sitchensis, 6e. Abieti lasiocarpae-Pinetum albicaulis, 6f. Phyllodoco glanduliflorae-Laricetum lyallii), 7. Pinion contortae (7a. Lonicero ledebourii-Pinetum contortae, 7b. Junipero depressae-Pinetum contortae)]. Ic: Continentality Index, Io: Ombrothermic Index, Itc: Compensated Thermicity Index, Tp: Yearly Positive Temperature, 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), Var: Bioclimatic variants (Stp: Steppic, Sbm: Submediterranean).

North American associations of 
Tsugetalia mertensiano-heterophyllae
North American biogeographic sectors
4.1a 4.1b 4.2a 4.2b 4.2c 4.2d 4.3 5.1
5. Tsugion heterophyllae + + + + + + + .
5a. Vaccinio ovati-Piceetum sitchensis . . + . . . . .
5b. Abieti amabilis-Piceetum sitchensis . . . + . . . .
5c. Rubo stellati-Piceetum sitchensis + + . . . . . .
5d. Tsugo he.-Sequoietum sempervirentis . . + . . . . .
5e. Gaultherio sh.-Pseudotsugetum me. . . + + . . . .
5f. Abieti g.-Pseudotsugetum menziesii . . . . + . . .
5g. Abieti am.-Tsugetum heterophyllae . . + + + . . .
5h. Piceo eng.-Tsugetum heterophyllae . . . + + + + .
6. Tsugion mertensianae + + + + + + + .
6a. Abieti ama.-Tsugetum mertensianae . . . + + . . .
6b. Abieti las.-Tsugetum mertensianae . . + + + + . .
6c. Tsugo mertens.-Abietetum procerae . . + + . . . .
6d. Tsugo mertens.-Piceetum sitchensis + + . . . . . .
6e. Abieti lasiocar.-Pinetum albicaulis . . . + + + . .
6f. Phyllodoco gl.-Laricetum lyallii . . . + . + + .
7. Pinion contortae . + + . + . . +
7a. Lonicero ledeb.-Pinetum contortae . . + . . . . +
7b. Junipero depre.-Pinetum contortae . + . . + . . .

Figure 20. Relationships between North American biogeographic sectors of North-Western Pacific Subregion and adjacent biogeographic territories and forest associations of Vb. Tsugetalia mertensiano-heterophyllae (5. Tsugion heterophyllae, 6. Tsugion mertensianae and 7. Pinion contortae). 4.1. Boreal Oceanic Alaskan Province: 4.1a. Boreal Oceanic Western Alaskan Sector, 4.1b. Boreal Oceanic Eastern Alaskan Sector, 4.2. Cascade Province: 4.2a. Oregonian-Vancouverian Coastal Sector. 4.2b. Cascade Ranges Sector. 4.2c. Canadian Coastal Mountains Sector. 4.2d. Columbia Mountains Sector. 4.3. Northern Rocky Mountain Province. 5.1. Northern Californian Province.

Within the most significant coniferous trees which could be used as differential species in the North-Western Pacific Subregion between Oceanic Temperate and Oceanic Boreal territories and bioclimates belonging to Cascade Province against Boreal Oceanic Alaskan Province it could be mentioned: Abies amabilis (Pacific silver fir), Abies grandis (grand fir), Abies procera (noble fir), Picea engelmannii var. engelmannii (Engelmann spruce), Pinus albicaulis (whitebark pine), Pinus monticola (western white pine), Pseudotsuga menziesii var. menziesii (coastal Douglas fir), Sequoia sempervirens (redwood) and Thuja plicata (western red cedar). Conversely, not any coniferous species could be mentioned in North America as particular for Oceanic Boreal against Oceanic Temperate, but there are several species that can grow in both bioclimatic and biogeographic territories: Abies lasiocarpa (subalpine fir), Chamaecyparis nootkatensis (Alaska cedar), Picea sitchensis (Sitka spruce), Pinus contorta var. contorta (shore lodgepole pine), Tsuga heterophylla (western hemlock) and Tsuga mertensiana (mountain hemlock).

Characteristic species: Abies amabilis, Abies procera x grandis, Acer glabrum var. douglasii, Adenocaulon bicolor, Anemone lyallii, Aquilegia formosa, Aster subspicatus, Bromus sitchensis var. sitchensis, Carex concinnoides, Carex inops, Coptis aspleniifolia, Corallorhiza mertensiana, Clintonia andrewsiana, Clintonia uniflora, Cornus suecica, Cypripedium montanum, Disporum hookeri var. hookeri, Disporum smithii, Equisetum variegatum subsp. alaskanum, Heuchera glabra, Hieracium aurantiacum, Huperzia miyoshiana, Lactuca biennis, Lilium columbianum, Listera caurina, Lonicera ciliosa, Luzula divaricata, Lycopodium clavatum var. integrifolium, Malus fusca, Menziesia ferruginea, Moneses uniflora subsp. reticulata, Oemleria cerasiformis, Oplopanax horridus, Osmorhiza purpurea, Pedicularis racemosa subsp. racemosa, Picea sitchensis, Pinus monticola, Pityopus californica, Polystichum andersonii, Polystichum dudleyi, Polystichum munitum, Rosa gymnocarpa, Rubus pedatus, Saxifraga odontoloma, Spiraea stevenii, Streptopus roseus var. curvipes, Symphoricarpos albus var. laevigatus, Taxus brevifolia, Tellima grandiflora, Thelypteris quelpaertensis, Thuja plicata, Tiarella trifoliata var. trifoliata, Tiarella trifoliata var. unifoliata, Tsuga xjeffreyi (T. heterophylla x mertensiana), Tsuga heterophylla, Vaccinium ovalifolium, Vancouveria planipetala, Viola glabella, Viola orbiculata.

North American associations of Tsugion heterophyllae North-Western Pacific biogeographic subsectors
1aa 1ba 1bb 2aa 2ab 2ac 2ba 2bb 2ca 2cb 2da 2db
5. Tsugion heterophyllae + + + + + + + + + + + +
5a. Vaccinio ovati-Piceetum sitchensis . . . + + + . . . . . .
5b. Abieti amabilis-Piceetum sitchensis . . . . . . + + . . . .
5c. Rubo stellati-Piceetum sitchensis + + + . . . . . . . . .
5d. Tsugo heter.-Sequoietum sempervirentis . . . + . . . . . . . .
5e. Gaultherio sh.-Pseudotsugetum menziesii . . . + + + + + . . . .
5f. Abieti grandis-Pseudotsugetum menziesii . . . . . . + + . . . .
5g. Abieti amabilis-Tsugetum heterophyllae . . . . + + + + + + . .
5h. Piceo engelmanii-Tsugetum heterophyllae . . . . . . + + + + + +

Figure 21. Relationships between biogeographic subsectors of North-Western Pacific Subregion and the associations of the Tsugion heterophyllae alliance. 4.1. Boreal Oceanic Alaskan Province, 4.1a. Boreal Oceanic Western Alaskan Sector: 1aa. Kenai Peninsula Subsector, 4.1b. Boreal Oceanic Eastern Alaskan Sector: 1ba. Glacier Coast Subsector, 1bb. Haines-Juneau Subsector. 4.2. Cascade Province, 4.2a. Oregonian Vancouverian Coastal Sector: 2aa. Oregonian Coastal Subsector, 2ab. Olympic Mountains Subsector, 2ac. Vancouverian Subsector, 4.2b. Cascade Ranges Sector: 2ba. Oregonian Cascade Subsector, 2bb. Washingtonian Cascade Subsector, 4.2c. Canadian Coastal Mountains Sector: 2ca. South Canadian Coastal Mountains Subsector, 2cb. North Canadian Coastal Mountains Subsector, 4.2d. Columbia Mountains Sector: 2da. Columbia Mountains Subsector, 2db. Bitterroot Range Subsector.