DISCUSSION AND RESULTS. DESCRIPTION OF PLANT COMMUNITIES

 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)

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.

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).

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.

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.