A Phytogeographical Classification of the North American Pacific Coast Based on Climate, Vegetation and a Floristic Analysis of Vascular Plants

Abstract EN

This study was designed to explore floristic variation along the Pacific coast from Cook Inlet, Alaska, to the southern tip of Baja California, Mexico.

Data corresponding to 965 phytosociological relevés (including 686 vascular plants) obtained by sampling 279 coastal sites were examined.

Using an objective classification system (Average Linkage Clustering), floristic data acquired in fieldwork were related to the macroclimates of the study area.

The registered taxa were grouped into phytogeographical elements, giving rise to a phytogeographical classification in which eight floristic provinces were distinguished.

Floristic differences among provinces were correlated with palaeoclimatic and palaeogeographical events.

The boreal and temperate provinces show high percentages of broadly distributed elements, whose origins can be found in the Boreotropical or Arcto-Tertiary geoflora that dominated the Northern Hemisphere during the Tertiary.

The floristically richest provinces are the three that occupy the Mediterranean zone, since these provinces harbour elements of Arcto-Tertiary and Madro-Tertiary geofloras.

The flora of tropical Baja California is characterised by a high number of taxa related to Neotropical flora, especially to those showing links with South America.