Serpentine Plant Life of Western North America

Serpentine plant life varies dramatically across western North America from north to south and, to a lesser extent, from the coast inland. At the latitudinal extremes in Alaska and Baja California, it follows patterns seen in other climatically harsh parts of the world (as discussed in chapter 10), but the species composition is not very distinctive and there are few endemics. In between, in Washington, Oregon, and especially in the California Floristic Province, lies a great diversity of distinctive serpentine vegetation types and endemic species. This chapter outlines the coarse patterns of variation in vegetation structure and endemic species richness across this region, as a prelude to chapter 12, which describes specific serpentine vegetation types in detail. Little has been published about the serpentine vegetation of Alaska and the Yukon. The Serpentine Slide Research Natural Area in central Alaska was described by Juday (1992) as having a mixture of white spruce (Picea glauca) and paper birch (Betula papyrifera) with Rosa acicularis, Juniperus communis, and Vaccinium uliginosum in the understory. Several herbs are shared with Swedish serpentines (e.g., Campanula rotundifolia, Minuartia rubella, Rumex acetosa, Saxifraga oppositifolia, Silene acaulis); several others showed northern range extensions on serpentine (see chapter 9). The ultramafic vegetation of Golden Mountain in southeast Alaska was described by Alexander et al. (1989) as alpine meadow containing forbs, graminoids, and low shrubs, with a transition through low shrubs and stunted lodgepole pines (Pinus contorta) down to spruce (Picea sitchensis)–hemlock (mainly Tsuga mertensiana) forest, with shrubs and some cedar (Chamaecyparis nootkatensis). The forest to alpine transition was lower on serpentine than on other soils. No serpentine endemic species are known from this region. From south–central British Columbia to central Oregon, serpentine has been described by Kruckeberg (1969, 1992) as supporting open stands of various conifers, which are either a subset of the species occurring in adjacent denser forests on other soils or represent elevational or geographic range shifts. Understories are sparse and may include graminoids, perennial forbs, and shrubs. On rocky ridgetops and at higher elevations and latitudes, these conifer plant communities give way gradually to alpine tundra.