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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The considerable economic value of the forests as a natural resource in the United States of America and Canada and the centralization of their management in the respective Departments of Agriculture was the reason for the development of a scientific understanding of their vaste forests. Within a short period of time, a close balance was achieved between explotation, regeneration and conservation of these resources. In consequence, the development of the knowledge of dendroflora and forest management and the increase in the autoecological and ecophysiological studies has been an unexpected reality.

The vegetation typology approaches, mainly physiognomic-ecological and bioclimatic are a very important ensemble of studies and publications which have been synthesized in the valuable and veteran work of Küchler (1964) in the Conterminous of United States, in the recent Canadian monographs of Pojar & al. (1987) and Klinka & al. (1996), and mainly through the inestimable chapters compiled in the book "North American Terrestrial Vegetation" by Barbour & Billings (1988).

The studies and synthetic publications on the Boreal and Temperate vegetation of North America were initiated more than sixty years ago with Halliday (1937) and Weaver & Clements" (1938) publications. The influence of the Braun-Blanquet phytosociological approach was evident in the analysis and synthesis of numerous studies and publications: Braun-Blanquet, Sissingh & Vlieger (1939), Knapp (1957, 1965), Grandtner (1960, 1966), Krajina (1959, 1960, 1965), Damman (1964), etc. However, for the last twenty years a global synopsis on North American potential natural vegetation following the Braun-Blanquet phytosociological methodology has been in progress. Within the publications involved in this project the works of Looman (1979, 1983/1987), Miyawaki, Iwatsuki & Grandtner (1994), Peinado & al. (1994, 1997/1998) and Rivas-Martínez (1997) should be mentioned as important.

Our present work is a continuation of the previously published "Syntaxonomical synopsis of the potential natural plant communities of North America, I" [Rivas-Martínez in Itinera Geobot. 10: 5-148 (20.06.1997)] and a part of a "Global Bioclimatics" project started in South America in 1977. In our first syntaxonomic compilation of climactical vegetation of North America we published four phytosociological classes, including the North American Mediterranean and Tropical potential climactical vegetation of South United States North of Mexico: I. Heteromelo arbutifoliae-Quercetea agrifoliae (evergreen sclerophyllous and late-deciduous, oceanic, thermo- and mesomediterranean mesoforests, woodlands and thicket communities of the Californian Region), II. Calocedro decurrentis-Pinetea jeffreyi (coniferous and mixed evergreen or broad-leaved deciduous, oceanic, supra-and oromediterranean forests of the Californian Region), III. Prosopido torreyanae-Fouquierietea splendentis (microphyllous-deciduous and succulent, xerophytic, thermo- and supratropical open scrublands to closed microforests of the Mexican Xerophytic Region), IV. Artemisio tridentatae-Juniperetea osteospermae (xerophytic, xeric and desertic continental, supra- and oromediterranean coniferous microforests, juniper-pinyon woodlands, and wooded or desertic steppe communities of the Great Basin Region). In this second part we focus on the potential natural Boreal and Temperate coniferous forests, broadly distributed throughout the territories of the North American Boreal and Rocky Mountain Regions. Moreover, we also include their evergreen, riparian and deciduous secondary forests (V. Linnaeo americanae-Piceetea marianae).