Vegetation responses and tephra characteristics following the 2008 eruption of Chaiten volcano, Chile

Background/Question/Methods

Volcanism is a globally important agent of disturbance. Eruptions create outstanding opportunities for investigating patterns and processes of ecosystem reassembly. The May 2008 eruptions of the Chaiten Volcano in southern Chile included powerful blast surges that toppled forests north of the edifice and tephrafalls that deposited fine-grained material and ash across an extensive area of Valdivian Rainforest; an ecoregion characterized by multi-layered forest of large statured broadleaf evergreen trees, abundant lianas, and numerous other epiphytes. From 2009 through 2012 we made annual trips to the volcano to document ecological responses of a variety of taxa, including trees and other vascular plants as well as the bryophyte community.  Here we present our work from nine plots (250m²) established in an area of toppled forest to document early patterns of plant succession and to assess the chemical and physical characteristics of pre-eruption soil and newly deposited tephra. In each plot we recorded plant species composition and cover (m²), tagged and measured tree seedlings and bole sprouts, measured woody debris, and gathered buried soil and tephra for assays of carbon, nitrogen, phosphorous, cation exchange capacity, major ions, and physical characteristics.

Results/Conclusions

Overstory trees were snapped-off or toppled and understory vegetation was buried beneath 30 cm of tephra. Although greatly reduced in number and cover, many residual understory species were present, and some downed tree boles were sprouting during the first post-eruption growing season (2009).  Mean species richness in our 250m² plots was 16.44 (SD 3.75) in 2011 and 24.67 (SD 3.12) by 2012. Increased richness values between 2011 and 2012 were primarily due to the establishment of early seral, wind-dispersed herbs, and to a lesser extent the emergence of buried residuals that penetrated upward through the tephra layer. Mean cover values increased from 8.1% in 2011 to 23.3% in 2012. Increases in cover were caused by rapid growth of residual fern and herb species and spread of newly colonized species (primarily Asteraceae). Seedlings from eight tree species were present within three years of the eruption. Survivorship of seedlings between 2011 and 2012 was 93.2% (n=88), while bole sprouts had a lower survivorship (30.1%, n=23). Tephra had lower total carbon and macronutrients compared to buried forest soil. Early post-eruption succession proceeded rapidly and low nutrient status of tephra has not inhibited colonization of several herbaceous species.