The post-eruption remeasurement of ecology reconnaissance plots installed before 1980 is comprised of five distinct parts. The most basic information was collected on 76 plots relocated during the summer of 1981. Photo points and reconnaissance level plots identical to the pre-eruption plots were installed.
Ashfall and blast zone sites have been sampled in order to monitor the recovery of insect and spider populations reduced by the May 1980 eruption. There were many survivors of the eruption in ashfall sites, especially of sedentary species and others that were protected in micro-refugia. Mortality in arthropod populations was correlated with the depth of the ashfall. Using ant colonies as an index, areas with 15 cm or less of ash deposited had species numbers similar to sites outside the devastated area. However in all areas arthropod populations have remained low compared to arthropod population recovery following clearcutting.
The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area. After the eruption, rates of erosion and plant cover were measured on tephra-covered hill slopes north of the volcano, some of which had been subject to one of three land-management practices. Rill erosion was initially greater than sheetwash, but its importance decreased comparatively quickly. On hill slopes left undisturbed since the eruption, rill erosion and sheetwash underwent a rapid and early decline due to the development of a stable rill network and the exposure and creation of more permeable and less erodible substrates. This decline was independent of plant recovery. Logging of trees downed by the eruption and scarification of the surface in preparation for reforestation slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. An experimental grass seeding program gave rise to a plant cover only after erosion had slowed, and then only in a limited range of environments.
The wetland sampling within the Mount St. Helens National Volcanic Monument is part of a larger study on the Gifford Pinchot National Forest. Information gathered will be used to classify riparian/wetland sites into identifiable ecological units that can be used to understand their environmental characteristics and prescribe appropriate management schemes. Study areas in the Monument are Coldwater Lake, Toutle River debris avalanche, and Goat Marsh Research Natural Area. Sample plots were selected to represent different community types (based on species composition and vegetation structure). Wetlands at Coldwater Lake and Toutle River debris avalanche were created as a result of the May 1980 eruption of Mount St. Helens, and thus can provide unique insight into the development of wetlands and plant succession.
The riparian sampling in the Mount St. Helens vicinity is part of a larger study that extends across the Gifford Pinchot National Forest. Streams sampled on the Mount St. Helens Ranger District are Kalama River, East Fork Fossil Creek, and Pin Creek. The purpose of gathering streamside plot data in this project is to produce a classification of streamside vegetative/geomorphic features. The sampling design is such that plant communities are juxtaposed on their geomorphic surfaces and then related to the stream channel itself. Because this project is being carried out in coordination with a separate Forest Riparian Inventory, we will later be able to relate our riparian information to the aquatic data being collected by the fisheries/hydrology programs.