Plant Ecology 129: 29–47, 1997. 29 c 1997 Kluwer Academic Publishers. Printed in Belgium. Vegetation formations and associations of the zonobiomes along the North American Pacific coast: from northern California to Alaska M. Peinado 1 , F. Alcaraz 2 , J. L. Aguirre 1 & J.M. a . Mart´ ınez-Parras 3 1 Departamento de Biolog´ ıa Vegetal, Universidad de Alcal´ a de Henares, E-28871 Alcal´ a de Henares, Madrid, Spain. E-Mail: BVMPL@jarifa.alcala.es; 2 Departamento de Biolog´ ıa Vegetal. Facultad de Biolog´ ıa. E-33600 Murcia, Spain; 3 I. B. Luca de Tena. C/ Pirineos s/n. E-41005 Sevilla, Spain; Author for correspondence Received 24 October 1995; accepted in revised form 26 July 1996 Key words: Bioclimatology, Biogeography, North America, Pacific coast, Phytosociology, Plant associations, Vegetation formations, Zonobiomes. Abstract This phytosociological study,carried out according to the Braun–Blanquet method and supported by cluster analysis, describes Walter’s zonobiomes along the North American Pacific coast between the California–Oregon state border and Alaska (USA), including some interior zones of British Columbia and the Yukon Territory (Canada). Twenty two floristic associations are identified and each is characterized by a unique floristic combination, a distinctive geographical range and particular bioclimatic or edaphic conditions. Introduction Walter (1985) divided the geo-biosphere into nine zon- obiomes, each one being a large and climatically uni- form environment characterized by distinctive zon- al vegetation. Peinado et al. (1994a) described the climax associations that characterize the zonobiomes between the southern tip of the Baja California Pen- insula (22 53 N) and approximately the California– Oregon state border (42 N). By means of phytoso- ciological relev´ es and field data taken between 1989 and 1992, the relations among zonobiomes, associ- ations, bioclimatic belts, ombrotypes and physiognom- ical formations thriving in that latitudinal range were described in that article. A sketch of these relations is shown in Table 1. Between 1992 and 1994 we carried out new phytosociological campaigns from northern California to Alaska, and registered 1156 new phytosociological relev´ es, 254 of which are now employed to analyze cli- max vegetation, describe dominant plant associations, and delimit zonobiomes, bioclimatic belts and ombro- types between the northern border of the already sur- veyed area and the latitude 64 N in Alaska. Survey area Except for some inland zones (see below) the surveyed area (Figure 1) stretches from 41 to 61 along the Northern American coast between sea level and the summit line of the mountain ranges of the northern part of the Pacific Border System (Brouillet & Whe- stone 1993). Two parallel belts of mountains dominate the area. In the north, the Chugach and Saint Elias Mountains of Alaska and the Insular Mountains of the islands of Queen Charlotte and Vancouver, con- stitute a seaward fringe of peaks. To the south, the Coast Ranges between northern California and Ore- gon (the Klamath and the Siskiyou) and Washington (including the Olympics) dominate the outer coastal topography. Throughout coastal British Columbia, the surveyed area stretches from sea level up to the summit line of the Coast Range, which separates it from the drier regions of the east. From the Fraser River Val- ley, in southeast British Columbia, southwards, across Washington and Oregon, the Cascades define the east- ern boundary. Between the Coast Ranges and the Cas- cades, the fertile but drier Puget Basin and Willamette Valley are formed.