Submitted to: Ecological Society of America Abstracts
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2004
Publication Date: 8/1/2004
Citation: Allen, M.F., Halvorson, J.J., Smith, J.L., Morris, S., Egerton-Warburton, L., Crisafulli, C., Macmahon, J. 2004. Life in the changing belowground during succession on Mount St. Helens. Page 12 IN Abstracts of the Meetings of the Ecological Society of America, August 1-6, 2004, Portland, Oregon. Interpretive Summary:
Technical Abstract: The eruption on Mount St. Helens initiated a pattern of disturbance resulting in a complex matrix of initial conditions in soils ranging from simple surface enrichment to a completely new substrate. This created a unique opportunity to study changing organisms and processes through time. We found several interesting responses when evaluating succession across the landscape. At the low-deposition areas, soil nutrient concentrations were moderate. In forests, the vertical layering remained through the 20 years following eruption and up to a century or more. Roots and mycorrhizal fungi concentrate in the organic layers. Animal digging mixed surface ash with buried soil in clear-cuts and meadows. Succession to diverse vegetation was rapid. In the high ashfall to blowdown areas, the nutrient resources were horizontally patchy, depending on animal disturbance and erosion. N and C were limiting in the inter-patch areas and plants and fungi colonized from the patch edges outward. These micro-scale patches were extremely important in succession dictating mycorrhizal interactions between plants that determined successional replacement. At the extreme, on the Pumice Plain, lupine-rhizobia symbioses initiated patches increasing organic matter and nutrients. Mycorrhizae concentrated in these patches dispersing most effectively by animal vectors. While the mycorrhizae did not initially improve growth of plants in these extreme nutrient-limiting conditions, the lupine patches provided C and N for establishing a mycelial matrix. That matrix facilitated the establishment of mycotrophic species. These diverse patches became attractants to more animals, particularly elk and rodents, in turn increasing the diversity of mycorrhizal fungi. The dispersed and diverse inoculum provided a feedback loop allowing even more species richness to establish and spreading plants, animals and fungi across the landscape. Thus, the dynamic interactions between plants, fungi, and animals become driving factors to the spread of communities across the disturbed landscape.