Upward movement of underground plant parts into deposits of tephra from Mount St. Helens

Abstract

The burial of plants is seldom studied but is potentially important in some ecosystems. For each of eight herbaceous species, about 10 individuals that survived burial by 7 – 15 cm of tephra were totally excavated during both 1981 and 1982. The long rhizomes of Achlys triphylla, Clintonia uniflora, and Smilacina stellata grew upward at an angle, so that 7% of rhizome and 3% of root dry weights were in the tephra in 1981; these values increased to 23 and 19%, respectively, in 1982. Burial reduced the number of shoots produced by each plant. Stolons of Rubus lasiococcus grew straight up and then spread across the tephra surface, although few roots were produced in the tephra. Plants of Arnica latifolia quickly moved rhizomes and roots into the tephra; 50% of underground dry weight was in the tephra by 1982. In two species with short rhizomes (Tiarella trifoliata and Valeriana sitchensis) there was an altered growth form; the rhizome elongated rapidly straight up to the tephra surface. The corm of Erythronium montanum was not relocated upward and it produced no roots in the tephra.