Subalpine vegetation on Mount St. Helens is recovering from the volcanic eruptions of May 1980. The recovery rate depends on the nature and intensity of destruction suffered by the vegetation at a particular site. New volcanic substrates were collected annually from 1980 through 1983 and bioassays were used to analyze their ability to support plant growth. The importance of soil structure and fertility was also investigated. Lack of soil nutrients appears to be a major factor limiting recovery. Soil weathering, the influx of airborne nutrients and the burrowing of small mammals enhance fertility. Some species now grow as well on these substrates as they do on an infertile loam. Despite the ability of some species to grow on these substrates, many areas of the mountain were devoid of vegetation as of October 1984. Immigration, a function of isolation, rather than soil development, may be the key to revegetation of totally devastated habitats.
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Moral et al. (1985) studied this question.