Initial Recovery of Subalpine Vegetation on Mount St. Helens, Washington

A network of permanent plots has been established on the subalpine slopes of Mount St. Helens. Plants in sites receiving only tephra or thin mud deposits survived the 18 May 1980 eruption and re-established themselves by late summer. Richness and cover on these substrates increased dramatically by 1981. Sites receiving thick cold mudflows have little vegetation after two growing seasons, and the few scattered individuals encountered are residual survivors, not seedlings. Subalpine sites destroyed by the directed blast, debris flow or pyroclastic flows had no surviving vascular plants and have yet to be recolonized. Such sites will require import of organic debris, nitrification and seed invasion for recovery to commence. Community analysis shows that subalpine herb composition is changing on all sites and that the magnitude of change, except on totally devastated sites, is proportional to the magnitude of the initial impact. Based on two seasons of observations, future changes in species number and cover are projected.