PARENT SESSION
Symposium #20: Extreme event analysis in ecology.
Sponsored by ESA Statistical Ecology and Long Term Studies Sections
Organized by: B. Li and R. G. Balice.
Thursday, August 9, 2001. 8:00 AM to 12:10 PM. Madison Ballroom A
Plant reestablishment on the Mount St. Helens' debris avalanche.
Dale, Virginia1, 1
ABSTRACT- Approximately sixty volcanoes erupt on the earth each year. The 20% of eruptions that occur on land impact nearby vegetation, often over large areas. The most studied ecological recovery after an eruption is that following the Mount St. Helens 1980 eruption. This eruption created a diverse landscape consisting of the crater, a 60-km2 debris avalanche, a 15-km2 pyroclastic flow, a 550-km2 area of downed trees bordered by 96-km2 of scorched trees, and massive mudflows. Each disturbance resulted in a unique pattern of plant survival and reestablishment depending on the life-form of species present before the eruption, topography, snow conditions, and disturbance characteristics. I have monitored vegetation reestablishment on the debris avalanche over the past 20 years using a series of permanent plots. There has been a gradual increase in plant diversity and cover with changes occurring over time in the dominant species. Shortly after the eruption, the Soil Conservation Service distributed seeds of nonnative species over part of the area with the intent of reducing erosion; these nonnative plants subsequently spread to some of my permanent plots. Twenty years later, the plots dominated by nonnative species have greater vegetation cover, yet differ in native plant diversity compared to plots which were not invaded. Plant recovery on the debris avalanche is slower than on less disturbed sites and is influenced by the characteristics of the invading species.
KEY WORDS: disturbance, recovery