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: Populetalia fremontii

Vg. Populetalia fremontii ordo nov hoc loco

Typus nominis: Populion fremontii alliancia nova hoc loco.

Cottonwood and other riparian wet deciduous forests developing along river banks, streams, flood plains, water courses, etc., and distributed throughout the Californian, Great Basin, Madrean and Mexican Xerophytic Regions in the Pluviseasonal, Xeric and Desertic, Oceanic and Continental, Mediterranean bioclimate territories, as well as Desertic and Xeric Tropical (supra-, meso- and thermomediterranean as well as from lower supratropical to upper thermotropical thermoclimatic belt areas). These forests grow on deep alluvial wet soils: fluvisols and locally, gleysols.

Bioclimatic diagnosis: Ic Ic 6-28, Io 0.3-3.6, Itc 200-520, Tp 1200-2800, Tps 500-1000, Tmin < 14, m < 9. [Mepo, Mepc, Mexo, Mexc, Mdc, Trxe, Trde-Tme, Mme, Sme, Ttr, Mtr, Str-Dry, Sar, Ari].

Within the Mediterranean and Tropical order Populetalia fremontii we recognize two alliances: Populion fremontii (Mediterranean), and Populion mesetae prov. (Tropical). 15. Populion fremontii: Pluviseasonal and Xeric Oceanic Mediterranean, as well as Xeric and Desertic Continental Mediterranean riparian cottonwood forests, occurring throughout the warm Californian and Great Basin territories. 15B. Populion mesetae: Xeric and Desertic Tropical spreading into Madrean and Mexican Xerophytic Regions (mainly in subtropical territories).

Characteristic species: Cephalanthus occidentalis, Fraxinus velutina, Populus deltoides subsp. wislizenii, Populus xhinckleyana (P. angustifolia x fremontii), Salix gooddingii, Salix laevigata, Salix taxifolia.

Syntaxa Ic Io Itc Tp Tps Tmin m Mb, Var
Vg. Populetalia fremontii 6-28 0.3-3.6 200-520 1200-2800 500-1000 < 14 < 9 Me, Tr
15. Populion fremontii 6-28 0.3-3.6 200-450 1200-2200 500-850 < 12 < 8 Me
15a. Platano rac.-Populetum fremontii 6-22 1.2-3.6 300-450 1600-2200 500-850 < 12 < 8 Me
15B. Populion mesetae 6-22 0.3-3.6 300-520 900-2800 700-1000 < 14 < 9 Tr, Pse

Figure 37. Synopsis of the bioclimatic diagnoses of syntaxa belonging to Populetalia angustifolio-deltoidis order. Relationships between the natural potential vegetation forests and the thresholds of the bioclimatic indexes and climatic parameter values [15. Populion fremontii (15a. Platano racemosae-Populetum fremontii)]. Ic: Continentality Index, Io: Ombrothermic Index, Itc: Compensated Thermicity Index, Tp: Yearly Positive Temperature Index, Ts: 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 (Me: Mediterranean, Tr: Tropical), Var: Bioclimatic variants (Pse: Pluviserotinal).

North American associations of
Populetalia angustifolio-deltoidis
North American biogeographic sectors
5.2 5.1d 5.1cb 6 7 8
Vg. Populetalia fremontii + + + + + +
15. Populion fremontii + + + + . .
15a. Platano racemosae-Populetum fremontii + + + . . .
15B. Populion mesetae . . . . + +

Figure 38. Relationships between North American biogeographic units and forest syntaxa of Vg. Populetalia fremontii (15. Populion fremontii, 15B. Populion mesetae). 5.2. Southern Californian Province. 5.1d. Great Valley Sector. 5.1cb. San Francisco and Monterrey Subsector. 6. Great Basin Region. 7. Mexican Xerophytic Region. 8. Madrean Region.