Vegetation change in the Mount St. Helens (U.S.A.) blast zone, 1979–1992

Abstract

Mount St. Helens, Washington, erupted in May 1980 leaving thousands of acres “devastated”; by its lateral blast. Vegetation recovery has taken place through both natural processes and replanting efforts on corporate and public lands. However, an area‐wide assessment of vegetation change has been lacking. Landsat MSS data have been used to calculate NDVI for 1979 and for even years from 1980 through 1992, and to determine date‐to‐date NDVI change. The largest area showing major vegetation cover increase is Weyerhaeuser property to the northwest of the mountain. Initial analysis indicates that timing of replanting is the most important factor in determining vegetative cover increase—the faster an area was replanted after the eruption, the more recovery is evident. Three‐date images indicate rapid green‐up by 1986 in quickly replanted areas of the blast zone. Natural regeneration has been much slower, although it is evident in parts of the National Volcanic Monument.