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: Tsugion heterophyllae

5. Tsugion heterophyllae alliancia nova hoc loco

[Piceion sitchensis Knapp in Geobot Mitt. 4: 27. 1957 (art. 8), Gaultherio-Pseudotsugion Knapp in Geobot Mitt. 4: 27. 1957 (art. 8), Tsugo-Laricion occidentalis Knapp in Geobot Mitt. 4: 27. 1957 (art. 8), Polysticho-Pseudotsugion Becking in Allgem. Forst und Jagdzeitung 127: 47. 1956 (art. 8), Gaultherio-Pseudetsugion Becking in Allgem. Forst und Jagdzeitung 127: 51. 1956 (art. 8)]

Typus nominis: Vaccinio ovati-Piceetum sitchensis associatio nova hoc loco.

North American climactical coniferous meso-, macro- and megaforests in the North-Western Pacific Subregion (Rocky Mountain Region) territories, spreading into Cascade and Boreal Oceanic Alaskan Provinces. They are distributed throughout the mesoboreal, hemiboreal, meso-, supra- and lower orotemperate and meso- and supramediterranean areas, with ombrotypes ranged from subhumid until ultrahyperhumid, and grow on andosols, cambisols, luvisols and podzols, with eutric, dystric, humic, umbric, gleyic or stagnic properties.

Bioclimatic diagnosis: Ic 5-23, Io 3.6-30.0, Itc < 270, Tp 570-1400, Tps 350-550, Tmin < 8, m <5. [Booc, Teho, Teoc-Tbo, Mbo, Mte, Ste, Hbo, Ote-Shw, Hum, Hhu, Uhh].

In a short synthesized synoptical table (table 14) we assemble ninety-one relevés from North-Western Pacific Subregion territories belonging to Tsugion heterophyllae alliance. The most important coniferous tree species which are involved in the canopies are: Abies amabilis (Pacific silver fir), Abies grandis (grand fir), Picea engelmannii var. engelmannii (Engelmann spruce), Picea sitchensis (Sitka spruce), Pinus monticola (western white pine), Sequoia sempervirens (redwood), Pseudotsuga menziesii var. glauca (Rocky Mountain Douglas fir), Pseudotsuga menziesii var. menziesii (coastal Douglas fir), Thuja plicata (western red cedar) and Tsuga heterophylla (western hemlock).

We distinguish within the allliance Tsugion heterophyllae eight different associations: 5a. Vaccinio ovati-Piceetum sitchensis: Hyperoceanic Temperate, upper mesotemperate to lower supratemperate, upper humid to lower ultrahyperhumid, occasionally submediterranean spreading into Oregonian-Vancouverian Coastal Sector territories, 5b. Abieti amabilis-Piceetum sitchensis: Oceanic Temperate, euoceanic, upper supratemperate, lower orotemperate and hemiboreal, hyperhumid to ultrahyperhumid, spreading into Canadian Coastal Mountains Sector territories, 5c. Rubo stellati-Piceetum sitchensis: Oceanic Boreal, euoceanic and semicontinental, upper humid to ultrahyperhumid, mainly mesoboreal spreading into Boreal Oceanic Alaska Province areas, 5d. Tsugo heterophyllae-Sequoietum sempervirentis: Hyperoceanic Temperate, euhyperoceanic, humid to lower hyperhumid, mesotemperate, submediterranean, spreading into Redwood District areas of the Oregonian Coastal Subsector, belonging to Oregonian-Vancouverian Coastal Sector (North-Western Pacific Subregion). 5e. Gaultherio shallonis-Pseudotsugetum menziesii: Oceanic Temperate, euoceanic, upper subhumid to humid, upper mesotemperate, supratemperate and lower orotemperate, spreading into Oregonian-Vancouverian and the Cascade Ranges Sectors territories, 5f. Abieti grandis-Pseudotsugetum menziesii: Oceanic Temperate, semicontinental and barely Continental Temperate, subcontinental, subhumid to lower humid, upper supratemperate and lower orotemperate spreading into Cascade Ranges Sector areas, 5g. Abieti amabilis-Tsugetum heterophyllae: Oceanic Temperate, euoceanic and semicontinental, humid to hyperhumid upper supratemperate and lower orotemperate spreading into Olympic Mountains and Vancouverian Subsectors, as well as in Cascade Ranges and Canadian Coastal Mountains Sectors, 5h. Piceo engelmannii-Tsugetum heterophyllae: Oceanic Temperate (semicontinental) and barely Continental Temperate (subcontinental), humid, lower orotemperate, spreading into Cascade Ranges territories, as well as in Canadian Coastal Mountains and Columbia Mountains Sectors (figures 19, 20, 21 and 22).

Characteristic species: Abies amabilis x procera, Abies grandis, Abies procera, Achlys triphylla, Allotropa virgata, Anemone deltoidea, Arceuthobium abietinum, Arceuthobium tsugense, Asarum caudatum, Campanula scouleri, Chamaecyparis lawsoniana, Chrysolepis crhysophylla var. minor, Corydalis scouleri, Dicentra formosa subsp. formosa, Dicentra formosa subsp. oregona, Disporum hookeri var. oreganum, Frangula purshiana, Gaultheria ovatifolia, Gaultheria shallon, Lonicera conjugialis, Mahonia nervosa, Maianthemum dilatatum, Marah oreganus, Mitella caulescens, Mitella diversifolia, Oxalis trilliifolia, Polystichum setigerum, Rhododendron macrophyllum, Sequoia sempervirens, Trillium ovatum, Vaccinium ovatum, Vaccinium parvifolium, Vancouveria hexandra, Viola sempervirens.

5a. Vaccinio ovati-Piceetum sitchensis associatio nova hoc loco

Hyperoceanic Temperate; upper mesotemperate to lower supratemperate; upper humid to lower ultrahyperhumid; frequently submediterranean (Ios2 < 2.5); mixed climactical coniferous macro- and megaforests of Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla), growing on deep humic, umbric, gleyic or stagnic cambisols, andosols or podzols in the Oregonian-Vancouverian Coastal Sector territories.

The dominant trees in the canopy are the conifers Picea sitchensis and Tsuga heterophylla but Thuja plicata can be also an important tree in these forests. Coastal Douglas fir (Pseudotsuga menziesii var. menziesii) is only occasionally present. In the understory are common some small trees, low shrubs, ferns and forbs such as: Vaccinium ovatum, Frangula purshiana, Sambucus arborescens, Rubus spectabilis, Gaultheria shallon, Polystichum munitum, Blechnum spicant and Maianthemum dilatatum. Also an important bryophytic layer with Eurhynchium oreganum, Plagiothecium undulatum and other species is also frequent. The secondary deciduous forests belong to the Aceri macrophylli-Alnetum rubrae association (Alno rubrae-Populion trichocarpae, Alno rubrae-Populetalia trichocarpae). If the temperature decreases going up from the coast, particularly in the Olympic Mountains and Vancouverian Subsectors territories, this forest association changes into Abieti amabilis-Tsugetum heterophyllae climax association. Also, going from the hyperoceanic coast in direction to the oceanic inland, particularly in leeward slopes expositions or interior river valleys, Picea sitchensis and Vaccinium ovatum become occasionals and very quickly disappear: the hyperoceanic hyperhumid forests of Vaccinio ovati-Piceetum sitchensis are obviously replaced by the oceanic humid and also climactical forest association: Gaultherio shallonis-Pseudotsugetum menziesii; in the herbaceous layer Achlys triphylla, Linnaea americana and Tiarella trifoliata var. unifoliata are common species. 

Bioclimatic diagnosis: Ic 6-12, Io 11.0-28.0, Itc 120-260, Tp 1000-1400, Tps 380-500, Tmin > 4, m > 2. [Teho, Teoc-Mte, Ste-Uhum, Hhu, Uhh-Sbm].

Table 15 shows 16 relevés from several hyperoceanic low coastal territories (0-150 m) of Oregon and Washington belonging to Oregonian and Olympic Mountains Subsectors (Oregonian-Vancouverian Coastal Sector).

Table 15
5a. Vaccinio ovati-Piceetum sitchensis

(Tsugion heterophyllae,Tsugetalia mertensiano-heterophyllae)

Altitude (1=10 m) 1 1 1 12 3 5 2 10 11 2 2 5 8 12 10 5 6
Number of species 21 21 21 22 23 24 24 24 24 26 28 28 28 29 30 34 25
Ordinal number 1 2 3 4 5 6 7 8 9 10 11 12* 13 14 15 16 17
Trees:
Picea sitchensis 5 5 4 3 3 5 5 5 2 3 3 5 2 4 4 4 V
Tsuga heterophylla . + 2 3 2 + 1 2 5 4 1 2 4 3 2 3 V
Thuja plicata . 1 + 2 2 . . + 2 1 3 + + . 1 1 IV
Alnus rubra 1 + 1 . + + 1 + . . 1 1 1 . . . IV
Pseudotsuga menziesii . . 1 . 2 + . . . . 2 . . . + . III
Characteristic species:
Polystichum munitum 2 2 2 2 3 2 3 4 3 3 3 3 2 2 2 3 V
Vaccinium ovatum 1 2 2 1 + 1 1 1 1 2 1 1 1 . 2 2 V
Gaultheria shallon 2 3 3 2 2 2 2 5 + 2 . 4 1 4 2 2 V
Frangula purshiana 1 . 1 + 2 1 1 + 1 1 2 1 + 2 + 1 V
Maianthemum dilatatum 3 5 2 . . 4 4 3 1 2 1 2 2 3 1 3 V
Rubus spectabilis 3 + + . . 2 . 1 . + 1 3 1 1 + 1 IV
Galium triflorum 1 . + . 1 1 1 + . . 2 1 . 2 . + IV
Vaccinium parvifolium 2 . 1 . 3 . 1 2 2 2 2 + . . . 2 IV
Sambucus arborescens 1 . 2 . 1 . 1 2 1 + + 2 . . . 1 IV
Disporum smithii . . . . . + 2 . 1 + 1 + . 1 1 1 IV
Menziesia ferruginea . + . 1 + . . 1 . 1 . 1 . . 2 3 III
Tiarella trifoliata . + . 1 . . . + . 1 . . 3 1 + 2 III
Oxalis oregana . . . . 3 . 2 1 3 . 3 . 3 . 3 1 III
Trillium ovatum . . . . 1 . . . 1 1 1 . + 1 1 + III
Dryopteris expansa . . . 1 . . . . 2 2 . . 2 . + + III
Vaccinium ovalifolium . . . 2 . . . . . 2 . . 3 1 1 1 III
Rubus leucodermis . . . . + 4 2 . 1 . . . . 1 . . III
Athyrium cyclosorum 2 . 3 . . . . . . . 1 2 . . . 2 III
Viola glabella . .   . 1 1 . . . . 3 . . . 1 + III
Marah oreganus + . . . . 2 . + . . . 2 . . . . II
Disporum oreganum . 1 . 1 . . . . . . . . 1 . . + II
Moneses uniflora . . . 1 . . . . . 2 . . . 2 1 . II
Stachys ciliata . . . . . . 2 . 2 . . 1 . . . + II
Luzula melanocarpa . . . . . . . 1 . + . 1 1 . . . II
Companion species:
Eurhynchium oreganum 2 2 2 2 2 . 2 3 2 4 2 3 3 3 2 2 V
Plagiothecium undulatum . 2 2 2 . 2 1 1 2 2 . 2 . 2 2 2 IV
Blechnum spicant . 2 . 3 . . + . 1 2 1 1 2 . 2 1 IV
Claytonia sibirica . . . . 1 . . + + . 2 1 1 1 1 1 IV
Athyrium americanum 3 . . . . . 1 . 2 1 . . + . 1 . III
Pteridium pubescens . + . . 1 2 . + . . 1 . . 1 . . III

Other species. Trees: Acer circinatum 1 in 13 and 14. Acer macrophyllum 1 in 9. Umbellularia californica 2 in 11. Characteristic species: Lonicera involucrata + in 2, 1 in 3 and 8. Oplopanax horridus + in 4 and 14, 1 in 15. Rubus parviflorus + in 5, 12 and 14. Stachys mexicana + in 1, 2 in 6. Polypodium glycyrrhiza 1 in 2, + in 6. Mitella pentandra + in 2, 1 in 13. Trientalis latifolia + in 3, 1 in 6. Rubus pedatus 3 in 4, 2 in 13. Osmorhiza purpurea + in 6 and 16. Sorbus scopulina 1 in 12, + in 14. Listera caurina 1 in 4. Hieracium albiflorum 1 in 7. Corydalis aurea + in 9. Ribes laxiflorum + in 10. Rhododendron macrophyllum 2, Mahonia nervosa 2, Dicentra formosa 1 in 11. Cardamine angulata 3 in 12. Monotropa uniflora 1, Corydalis scouleri + in 13. Amelanchier alnifolia 1, Oemleria cerasiformis 1, Actaea arguta + in 14. Salix sitchensis 1 in 1. Boykinia occidentalis + in 15. Tolmiea menziesii + in 16. Companion species: Hylocomium splendens 3 in 4, 7 and 14, 2 in 10 and 15. Lysichiton americanus 3 in 1, 2 in 3, 1 in 10, + in 15 and 16. Rhizomnium magnifolium 4 in 4, 2 in 8 and 13, 1 in 12 and 16. Ilex aquifolium + in 7, 3 and 16, 2 in 14. Hedera helix 2 in 1, 1 in 5 and 12. Heracleum maximum + in 2 and 16, 1 in 6. Rubus ursinus + in 5, 1 in 7 and 9. Carex obnupta 1 in 1, 2 in 3. Calamagrostis nutkaensis 2 in 1, 1 in 6. Bromus vulgaris + in 2, 1 in 16. Iris douglasiana 2 in 6, 1 in 11. Isothecium myosuroides 2 in 14 and 15. Sphagnum girgensohnii 2 in 4. Satureja douglasii + in 7. Lonicera vacillans 1 in 11. Eurhynchium praelongum 2 in 13. Mycelis muralis 1 in 14. Neckera douglasii 2 in 15.

Localities: 1. Oregon: Coos Co. Bandon. Ferry Creek. 43º07'N-124º23'W. W, 5%, 35 m, 100 cm, 1000 m2 (reg. 1998a: 24). 2. Washington: Clallam Co. Olympic Mountains. Olympic National Park. Ruby Beach. Cedar Creek. 47º43'N-124º19'W. W, 5%, 15 m, 60 cm, 1000 m2 (reg. 1998a: 55). 3. Oregon: Tillamook Co. Rockaway Beach. Spring Beach. 45º38'N-123º55'W. S, 2%, 35 m, 80 cm, 1000 m2 (reg. 1998a: 47). 4. Washington: Grays Harbor Co. Neilton-Quinault Lake. Quinault Research Natural Area. 47º26'N-123º51'W. N, 5%, 55 m, 140 cm, 2000 m2 (reg. 1998a: 53). 5. Oregon: Lincoln Co. Waldport. Alsea River. 44º25'N-124º02'W. N, 5%, 40 m, 120 cm, 1000 m2 (reg. 1996: 95). 6. Oregon: Curry Co. Samuel H. Boardman State Park. Arch Rock Point. Miller Creek. 42º11'N-124º22'W. W, 20%, 40 m, 100 cm, 1000 m2 (reg. 1998a: 18). 7. Oregon: Lane Co. Yachats. Neptum State Park. Cummnins Creek Road. Cummnins Creek. 44º16'N-124º07'W. W, 5%, 45 m, 150 cm, 1000 m2 (reg. 1997: 6). 8. Oregon: Tillamook Co. Manzanita-Tolovana Park. Oswald West State Park. Necarney Creek. 45º45'N-123º57'W. W, 5%, 50 m, 250 cm, 2000 m2 (reg. 1998a: 49). 9. Oregon: Lincoln Co. Newport-Cutler City. Fogarty Creek State Park. 44º21'N-124º03'W. S, 20%, 50 m, 180 cm, 1000 m2 (reg. 1997: 8). 10. Washington: Pacific Co. Middle Nemah. Middle Nemah River. 46º29'N-123º53'W. NE, 25%, 50 m, 100 cm, 2000 m2 (reg. 1998a: 51). 11. Oregon: Coos Co. Coquille. Rink Creek. 43º09'N-124º11'W. N, 25%, 35 m, 80 cm, 1000 m2 (reg. 1998a: 28). 12. Oregon: Tillamook Co. Rockaway Beach. Spring Beach. 45º39'N-123º55'W. W, 10%, 45 m, 150 cm, 1000 m2, holotypus ass. (reg. 1998a: 48). 13. Washington: Jefferson Co. Queets-Clearwater. Olympic Mountains. Olympic National Park. 47º35'N-124º16W. S, 5%, 60 m, 150 cm, 2000 m2 (reg. 1998a: 54). 14. Washington: Clallam Co. Shuwah-Lake Pleasant. Lake Creek. 48º03'N-124º23'W. SW, 5%, 55 m, 80 cm, 2000 m2 (reg. 1998a: 56). 15. Washington: Pacific Co. Raymond. Butte Creek. 46º43'N-123º44'W. SW, 15%, 60 m, 120 cm, 4000 m2 (reg. 1998a: 52). 16. Oregon: Tillamook Co. Manzanita-Tolovana Park. Oswald West State Park. Necarney Creek. 45º45'N-123º58'W. W, 15%, 50 m, 200 cm, 2000 m2 (reg. 1998a: 50). 17. Synthesized table.

Type relevé (holotypus): Table 15, relevé n. 12. Rivas-Martínez reg. 1998a: 48. 13.06.98, made with Drs. Costa, Ladero & Sánchez-Mata. Site: Oregon: Tillamook Co. Rockaway Beach. Spring Beach. 45º39'N-123º55'W. 50 m, W, 10%, 45 m, 150 cm, 1000 m2. Physiognomy and habitat: Mature Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) megaforest. Estimated bioclimatic factors: Hyperoceanic Temperate (Ic ~ 10), upper mesotemperate (Itc ~ 200), lower hyperhumid (Io ~ 12.0), Positive Summer Temperature Tps ~ 480. Biogeographic location: Rocky Mountain Region, North-Western Pacific Subregion, Cascade Province, Oregonian-Vancouverian Coastal Sector, Oregonian Coastal Subsector. Floristic combination: Linnaeo-Piceetea characteristic species, trees: 1 Alnus rubra, 5 Picea sitchensis, + Thuja plicata, 2 Tsuga heterophylla. Others: 3 Cardamine angulata, + Disporum smithii, 1 Frangula purshiana, 1 Galium triflorum, 4 Gaultheria shallon, 1 Luzula divaricata, 2 Maianthemum dilatatum, 2 Marah oreganus, 1 Menziesia ferruginea, 3 Polystichum munitum, + Rubus parviflorus, 3 Rubus spectabilis, 2 Sambucus racemosa subsp. pubens var. arborescens, 1 Sorbus scopulina var. scopulina, 1 Stachys ciliata, + Vaccinium parvifolium. Companion species: 2 Athyrium filix-femina var cyclosorum, 1 Blechnum spicant, 1 Claytonia sibirica, 3 Eurhynchium oreganum, 1 Hedera helix, 2 Plagiothecium undulatum.

Map Figure 22. Distribution of the forest plant associations belonging to alliance 5. Tsugion heterophyllae: 5a. Vaccinio ovati-Piceetum sitchensis (Oregonian-Vancouverian Coastal Sector), 5b. Abieti amabilis-Piceetum sitchensis (Canadian Coastal Mountains Sector), 5c. Rubo stellati-Piceetum sitchensis (Boreal Oceanic Alaska Province). 5d. Tsugo heterophyllae-Sequoietum sempervirentis (South corner of Oregonian Coastal Subsector), 5e. Gaultherio shallonis-Pseudotsugetum menziesii (Oregonian-Vancouverian Coastal and Cascade Ranges Sectors), 5f. Abieti grandis-Pseudotsugetum menziesii (Cascade Ranges and Columbia Mountains Sector), 5g. Abieti amabilis-Tsugetum heterophyllae (Columbia Mountains, Canadian Coastal Mountain and Cascade Ranges Sectors).

5b. Abieti amabilis-Piceetum sitchensis associatio nova hoc loco

Oceanic Temperate; supratemperate and hemiboreal; hyperhumid and ultrahyperhumid; Sitka spruce (Picea sitchensis) and Pacific silver fir (Abies amabilis) diverse climactical coniferous macroforests in the Canadian Coastal Mountains Sector territories.

Bioclimatic diagnosis: Ic 11-18, Io 12.0-30.0, Tp 720-1000, Tps 380-430, Tmin < 4, m < 2. [Teoc-Ste, Ote-Hhu, Uhh].

Table 16 shows five relevés from British Columbia in the lower Skeena River bassin, sampled in several upper supratemperate hyperhumid territories, which belong to North Canadian Coastal Mountains Subsector. Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata) and Pacific silver fir (Abies amabilis) are the commonest conifers in the wet macroforests. In the understory are also frequent some shrubs, forbs and herbaceous plants such as: Menziesia ferruginea, Cornus canadensis, Vaccinium membranaceum, Tiarella trifoliata var. trifoliata, Lysichiton americanus and Oplopanax horridus; the last two forbs grow on soils with stagno-gleyic and gleyic humid character.

Type relevé (holotypus): Table 16, relevé n. 4. Rivas-Martínez reg. 1997: 26. 27.08.97, made with Dr. Sánchez-Mata and P. Rodríguez-Rojo. Site: British Columbia: Prince Rupert. Diana Lake. 64º15'N-130º14'W. 50 m, W, 30%, 25 m, 45 cm, 1000 m2. Physiognomy and habitat: Mature Sitka spruce (Picea sitchensis), Pacific silver fir (Abies amabilis), Western hemlock (Tsuga heterophylla) and western red cedar (Thuja plicata) macroforest. Estimated bioclimatic factors: Oceanic Temperate (Ic ~ 13), lower hemiboreal (Itc ~ 90), lower ultrahyperoceanic (Io ~ 25), Positive Summer Temperature Tps ~ 390. Biogeographic location: Rocky Mountain Region, North-Western Pacific Subregion, Cascade Province, Canadian Coastal Mountains Sector. Floristic combination: Linnaeo-Piceetea characteristic species, trees: 2 Abies amabilis, 3 Picea sitchensis, 2 Thuja plicata, 2 Tsuga heterophylla. Others: + Clintonia uniflora, 3 Coptis aspleniifolia, 3 Cornus canadensis, 1 Gaultheria shallon, 2 Linnaea americana, 1 Maianthemum dilatatum, 1 Maianthemum stellatum, 4 Menziesia ferruginea, 2 Oplopanax horridus, + Rubus spectabilis, 3 Vaccinium membranaceum. Companion species: 1 Blechnum spicant, 2 Bryum capillare, 1 Caltha leptosepala subsp. howellii, 2 Conocephalum conicum, + Equisetum arvense var. boreale, 3 Hylocomium splendens, 1 Lobaria pulmonaria, 2 Lysichiton americanus, 2 Rhytidiadelphus loreus, + Rubus idaeus subsp. strigosus, 2 Sphagnum papillosum.

5c. Rubo stellati-Piceetum sitchensis associatio nova hoc loco

Oceanic Boreal; mesoboreal and barely thermoboreal; hyperhumid and ultrahyperhumid; Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) climactical meso- and macroforests in the Boreal Oceanic Alaskan Province territories, growing on dystric and gleyic podzols.

Bioclimatic diagnosis: Ic 14-21, Io 10.0-40.0, Tp 570-720, Tps 370-420, Tmin < -1, m < -2. [Booc-Tbo, Mbo, Sbo-Hhu].

Table 17 shows five relevés sampled throughout the Alaska and contiguous British Columbia territories belonging to Haines-Juneau Subsector (Boreal Oceanic Alaskan Province). The conifers and tallest trees in this association are Tsuga heterophylla and Picea sitchensis, being absent in the Boreal-Temperate southern boundary the rest of the Temperate characteristic coniferous trees of Tsugion heterophyllae alliance such as Thuja plicata, Abies amabilis and Pseudotsuga menziesii var. menziesii. Somewhat occurs with many understory sciophilous characteristic species such as Achlys triphylla, Asarum caudatum, Clintonia uniflora, Galium triflorum, Gaultheria shallon, Maianthemum stellatum, Polystichum munitum, Trillium ovatum, Vaccinium parviflorum and Vancouveria hexandra.

Rubo stellati-Piceetum sitchensis association is close to the upper mesoboreal and supraboreal Tsugo mertensianae-Piceetum sitchensis association growing in almost the same biogeographic territories but with different dominant species of Tsuga in the canopy and also some sciophilous differential species between both such as Rubus arcticus subsp. stellatus, Tiarella trifoliata var. trifoliata and Vaccinium membranaceum for the first association, and conversely, Rubus chamaemorus, Linnaea americana and Pyrola asarifolia.

Type relevé (holotypus): Table 17, relevé n. 1. Rivas-Martínez reg. 1994a: 155. 25.08.94, made with Drs. Asensi, Costa, Fernández-González & Molero. Site: Alaska. Haines, Chilkoot. 59º13'N-135º30'W. 30 m, E, 20%, 40 m, 90 cm, 400 m2. Physiognomy and habitat: Mature Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) macroforest. Estimated bioclimatic factors: Oceanic Boreal (Ic ~ 19), lower mesoboreal (Tp ~680), upper humid (Io ~ 11.0), Positive Summer Temperature Tps ~ 400. Biogeographic location: Rocky Mountain Region, Boreal Oceanic Alaskan Province, North-Western Pacific Subregion, Boreal Oceanic Eastern Sector, Haines-Huneau Subsector. Floristic combination: Linnaeo-Piceetea characteristic species, trees: 2 Picea sitchensis, 4 Tsuga heterophylla. Others: 3 Cornus canadensis, 3 Dryopteris expansa, + Goodyera oblongifolia, 2 Gymnocarpium dryopteris, 1 Maianthemum dilatatum, 3 Menziesia ferruginea, 2 Moneses uniflora subsp. reticulata, 2 Orthilia secunda, 2 Rubus pedatus, 2 Rubus stellatus, 1 Tiarella trifoliata var. trifoliata, 1 Oplopanax horridus, 1 Ribes lacustre, 3 Vaccinium membranaceum, 2 Vaccinium ovalifolium. Companion species: 5 Hylocomium splendens, 1 Plagiochila asplenioides, 1 Rhytidiadelphus triquetrus.

Table 17
5c. Rubo stellati-Piceetum sitchensis

(Tsugion heterophyllae-Tsugetalia mertensiano-heterophyllae)

Altitude (1=10 m) 3 47 59 3 65 30
Number of species 22 22 24 26 28 24
Ordinal number 1* 2 3 4 5 6
Trees:
Tsuga heterophylla 4 4 3 4 4 V
Picea sitchensis 2 3 4 3 3 V
Characteristic species:
Menziensia ferruginea 3 3 3 4 4 V
Cornus canadensis 3 2 2 2 3 V
Dryopteris expansa 3 1 1 3 2 V
Gymnocarpium dryopteris 2 3 3 3 2 V
Vaccinium ovalifolium 2 3 3 1 4 V
Rubus pedatus 2 2 2 2 1 V
Rubus stellatus 2 2 1 2 2 V
Tiarella trifoliata 1 + 1 2 2 V
Oplopanax horridus 1 + 1 2 + V
Streptopus americanus + 1 1 2 2 V
Alnus sinuata + . 2 + 1 IV
Vaccinium membranaceum 3 3 . 2 . III
Orthilia secunda 2 . 1 . 2 III
Trientalis arctica . 1 1 . + III
Sorbus sitchensis . 1 + . 1 III
Veratrum viride . + 1 . + III
Athyrium cyclosorum . . 1 + 1 III
Companion species:
Plagiochila asplenioides 1 2 3 2 2 V
Hylocomium splendens 5 1 2 3 . IV
Equisetum boreale . . + + 2 III

Other species. Characteristic species: Moneses reticulata 2 in 1 and 4. Maianthemum dilatatum 1 in 1, + in 4. Ribes lacustre 1 in 1, + in 4. Senecio triangularis + in 3, 1 in 5. Galium triflorum + in 3 and 5. Goodyera oblongifolia + in 1. Streptopus brevipes 3, Rosa sayi + in 2. Ribes laxiflorum +, Viburnum edule +, Actaea arguta + in 4. Platanthera stricta 1, Valeriana sitchensis + in 5. Companion species: Rhytidiadelphus triquetrus 1 in 1, 3 in 2. Sphagnum girgensohnii 2 in 2, 1 in 4. Pleurozium schreberi 2 in 3, 1 in 5. Lysichiton americanum 1 in 4. Heracleum maximum 1, Sanguisorba canadensis +, Caltha palustris + in 5.

Localities: 1. Alaska: Haines, Chilkoot. 59º13'N-135º30'W. E, 20%, 40 m, 90 cm, 1000 m2, holotypus ass. (reg. 1994a: 155). 2. British Columbia. Pleasant Camp, USA border. 59º30'N-136º40'W. N, 10%, 45 m, 100 cm, 500 m2. (reg. 1994a: 162). 4. Alaska. Haines. 59º15'N-135º27'W. SE, 20%, 30 m, 70 cm, 500 m2. (reg. 1994a: 139). 3. British Columbia. Rainy Holow. 59º54'N-135º25'W. S, 10%, 30 m, 80 cm, 500 m2. (reg. 1994a: 163 bis). 5. British Columbia. Rainy Holow. 59º56'N-136º44'W. SW, 15%, 35 m, 100 cm, 500 m2. (reg. 1994a: 163). 6. Synthesized table.