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: Ledo decumbentis-Betuletalia glandulosae

Vh. Ledo decumbentis-Betuletalia glandulosae ordo novo hoc loco

[Betuletalia pumilo-glanduliferae Kojima in Phytocoenologia 14(1) 6. 1986 (art. 5, 8)]

Typus nominis: Salici pulchrae-Betulion glandulosae alliancia nova hoc loco.

North American climactical, permanent snowdrift and boggy dwarf willow and dwarf birch tundra communities (dwarf and low sprawling thickets and scrubs) distributed throughout the Hyperoceanic, Oceanic, Subcontinental and Continental Boreal areas, as well as Oceanic and Continental Polar, and Continental Temperate (subcontinental, eucontinental); supra- and oroboreal subhumid to hyperhumid, mesopolar subhumid to humid, upper orotemperate and lower cryorotemperate humid and hyperhumid territories. Widespread throughout the North American Boreal and Circumarctic Regions, these communities reach the high mountain areas of the Rocky Mountain Region. These tall and low tundra vegetation communities grow on gelic, gleyic or hystic podzols, histosols and gleysols. In windy slopes, ridges or crests habitats, with few or without winter permanent snow cover, they usually are in contiguity with the arctic-alpine dwarf-shrub windy heath snowless tundra communities belonging to the Loiseleurio-Vaccinietea class, and in a very long time snowy habitats, with the snowdrift dwarf-shrubby communities belonging to the Salicetea herbaceae class.

Bioclimatic diagnosis: Ic 10-40, Io 2.8-30.0, Tp 180-700, Tps 170-400, Tmin < 0, m < -2. [Boho, Booc, Bosc, Boco, Boxe, Pooc, Poco, Poxe, Teoc, Teco-Mbo, Sbo, Obo, Mpo-Dry, Shu, Hum, Ote, Cte-Hhu, Uhu].

Within the order Ledo decumbentis-Betuletalia glandulosae it is possible to distinguish several groups of communities: Firstly, one western inland alliance distributed throughout the Alaska, British Columbia and Canadian North West Territories: 16. Salici pulchrae-Betulion glandulosae, and secondly, in the eastern of the continent and big islands (Greenland, Baffin, Newfoundland, Labrador) as well as localized in North Canadian Appalachian territories, it would be possible to recognize other alliance: 16B. Betulion minoris prov. growing in barrens, rocky slopes and bogs and characterized by Betula michauxii, Betula minor, Betula nana subsp. nana and Salix serissima (figures 40, 41, 42).

In a short synthesized table (table 67) we assemble 12 relevés from Alaska, British Columbia and Yukon territories belonging to the alliance Salici pulchrae-Betulion glandulosae: 16a. Salici barclayi-Betuletum glandulosae (snowdrift habitats), 16b. Vaccinio microphylli-Betuletum glandulosae (winter snow cover habitats) and 16c. Salici pulchrae-Betuletum exilis (boggy habitats).

Characteristic species: Alnus viridis subsp. crispa, Betula glandulosa, Betula pumila var. glandulifera, Betula xsargentii (B. glandulosa x pumila), Kalmia polifolia, Ledum palustre subsp. decumbens, Salix arctica, Salix candida, Salix farriae, Salix myrtillifolia, Salix planifolia subsp. planifolia.

To classify the associations and alliances of Ledo-Betuletalia glandulosae order we publish an easy floristic and biogeographic key.

1 With Betula michauxii, Betula minor or Betula nana (North-Eastern America, East of Hudson Bay in the Appalachian and Newfoundlandian Sector to Labrador and Baffin Island) 16B. Betulion minoris
With Betula exilis, Salix pulchra or Artemisia arctica, but without Betula michauxii, Betula minor or Betula nana (North-Western America, west of Hudson Bay) 2
2 With Betula exilis, Salix hastata and Carex lugens (histosols) 16c. Salici pulchrae-Betuletum exilis
With Artemisia arctica or Salix acutifolia, but without Betula exilis, Salix hastata or Carex lugens (podzol or gleyic soils) 3
3 With Salix barclayi or Rubus arcticus, but without Ledo decumbens or Vaccinium microphyllum (snowdrift habitats) 16a. Salici barclayi-Betuletum glandulosae
With Vaccinium microphyllum or Ledum decumbens, but without Salix barclayi or Rubus arcticus (with winter snow cover) 16b. Vaccinio microphylli-Betuletum glandulosae
Syntaxa Ic Io Itc Tp Tps Tmin m Mb, Var
Vh. Ledo decum.-Betuletalia glan. 10-40 2.8-30.0 - 180-700 170-400 < 0 < -2 Po, Bo, Te
16. Salici pul.-Betulion glandulosae 10-40 2.8-30.0 - 180-500 180-300 < 0 < -2 Po, Bo, Te
16a. Salici b.-Betuletum glandulosae 10-32 6.0-30.0 - 300-500 240-300 < 0 < -2 Bo
16b. Vaccinio m.-Betuletum glandul. 21-38 3.6-24.0 - 250-500 200-300 < -6 < -10 Po, Bo, Stp
16c. Salici pulchrae-Betuletum exilis 10-40 2.8-30.0 - 180-450 170-280 < 0 < -2 Po, Bo, Stp
16B. Betulion minoris 21-34 9.0-22.0 - 200-700 170-400 < -4 < -9 Bo, Te

Figure 40. Synopsis of the bioclimatic diagnoses of syntaxa belonging to Ledo decumbentis-Betuletalia glandulosae order. Relationships between the natural potential vegetation forests and the thresholds of the bioclimatic indexes and climatical parameter values [16. Salici pulchrae-Betulion glandulosae (16a. Salici barclayi-Betuletum glandulosae, 16b. Vaccinio microphylli-Betuletum glandulosae, 16c. Salici pulchrae-Betuletum exilis), 16B. Betulion minoris]. 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, Po: Polar, Te: Temperate), Var: Bioclimatic variants (Stp: Steppic).