Abstract
To determine the effects of tephra (volcanic aerial ejecta) on forest understory plants, six sites were chosen along a tephra depth gradient (23 to 150 mm) northeast of Mount St. Helens, USA. All sites were in old forests beyond the limits of direct blast damage from the volcanic eruption. At each site, 150 one m2 plots were permanently marked; all tephra was removed from 50 of these in 1980. Cover and density of plant species were recorded during 1980, 1981, and 1982.
Tephra 23 mm deep had almost no effect on cover and density of vascular plants, and reduced bryophyte cover for only two years. Tephra 45 mm deep destroyed almost all bryophytes. Although damaged by 45 mm tephra, deciduous herbs recovered by 1982, but some evergreen species did not. Tephra 75 mm deep reduced herb cover in 1982 to 32% and density to 26% of that in cleared plots. At two sites with an average tephra depth of 150 mm, almost all herbs were eliminated except in microsites where tephra was thin, but shrub abundance was greatly reduced only where snow had been present during tephra deposition. Almost all cover was contributed by plants established previous to the eruption; seedling cover never exceeded 0.2%. Refugia with thin tephra, resulting from erosion, were vital to the survival of many species, especially bryophytes.
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Nomenclature of vascular plants follows Hitchcock & Cronquist (1973); moss nomenclature follows Lawton (1971).
We thank T. Hill, C. Halpern and B. Smith for field assistance. The USDA Forest Service, and especially J. F. Franklin, facilitated entry into the restricted area around Mount St. Helens. This word was supported by the National Science Foundation, USDA Science and Education Administration, and the U.S. Forest Service Pacific Northwest Forest and Range Experiment Station.
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Antos, J.A., Zobel, D.B. Recovery of forest understories buried by tephra from Mount St. Helens. Vegetatio 64, 103–111 (1986). https://doi.org/10.1007/BF00044786
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DOI: https://doi.org/10.1007/BF00044786