The vegetation of pre- and post-eruption Kasatochi Island, central Aleutian Islands, within the hyperoceanic sector of the northern boreal subzone, was studied to provide a general field assessment of plant survival following the 2008 volcanic eruption. Pre-eruption plant community data, collected during August 2001 and 2003, indicated Kasatochi comprised lush herbaceous meadows and dwarf shrubs. The pre-eruption data provided a context permitting us to follow post-eruption successional processes. The eruption produced large quantities of volcanic sediment blanketing the living-green mantle of the island resulting in significant ecologic consequences. Rapid erosion is ongoing, with little to deter the erosive effects of flowing water from high annual precipitation. Newly formed volcanic islands depend on long-distance dispersal of organisms for community reassembly. However, on post-eruption Kasatochi, surviving (legacy) plants, while sparse, may contribute predominantly to community reassembly; the contribution of colonizers is not yet determined.
Pre- and post-eruption relevé data were analyzed using multivariate analysis. Post-eruption soil was analyzed from selected sites for chemical and textural properties. Ten major vegetation types comprising legacy species were described. We found that 1) plants that apparently survived the eruption dominated early plant communities. The most diverse post-eruption community most closely resembled a widespread pre-eruption type. Two species (Leymus mollis and Lupinus nootkatensis), dominate most legacy communities. 2) In 2009, no mature plants produced seeds: post-eruption plants were mostly mature vegetative perennial plants from rhizomes and seedlings. However, by 2011, seeds were observed on Leymus, Lupinus and Ranunculus occidentalis. 3) There is little evidence for inter-island colonization by any species, presumably because the distance between islands (at least 20 km) is great. In the future, plant propagules are expected to reach Kasatochi via three different dispersal mechanisms (anemochory, zoochory, and hydrochory). We initiated genetic admixture analyses of seven plant species characterized by one or more of these dispersal mechanisms to determine the contribution of colonizer vs. legacy plants to community reassembly. 4) Nine years after the eruption, the island remains essentially barren, although biomass increased, for Leymus, and most recently, Lupinus, since 2009. 5) There are substantial differences between the pre- and post-eruption bryophyte flora.