OOS 45-4 - Early ecological responses of forest ecosystems to explosive volcanism in southern Chile

Thursday, August 10, 2017: 2:30 PM
D135, Oregon Convention Center
Mauro E González1,2, Pilar Fierro1, Mauricio Montiel1, Romina Novoa-Melson1 and Charles M. Crisafulli3, (1)Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile, Valdivia, Chile, (2)Center for Climate and Resilience Research, Santiago, Chile, (3)Mount St. Helens National Volcanic Monument, U.S. Forest Service

Chile has about 500 active volcanoes, making it a global hotspot for volcanism. Many of these volcanoes have a rich contemporary eruptive history; for example, 33 volcanoes erupted since 1900 and 11 between 2000 and 2015. Eruption magnitude has varied from small to large, and a few are among the largest eruptions globally in the past 100 years. These eruptions have caused modest to extreme change in ecosystems across Chile, but have received little attention by ecologists until recently. To address this dearth of knowledge on ecological responses of biota to volcanism in Chile, we took advantage of three contemporary volcanic eruptions: Chaiten (2008), Cordon Caulle (2011), and Calbuco (2015). These explosive style eruptions included a variety of volcanic disturbance processes, but were dominantly tephra fall events. All volcanic sites studied were in Valdivian temperate rainforest, but varied somewhat in elevation and plant community composition and structure. Permanent plots were established in each location, following protocols developed at Mount St. Helens (USA), to assess immediate and longer-term responses of vegetation, forest floor organic material, ground-dwelling arthropods, small mammals (only Calbuco), and the chemical and physical characteristics of tephra.


At Chaiten, a small pyroclastic density current swept down the north flank of the volcano creating a disturbance gradient that included zones of tree removal, toppled forest and scorched, standing forest. The number of surviving plant species was inversely related to disturbance intensity (toppled forest 10 to 16 species versus tree-removal 2-3). Survivorship was related to species’ resprouting capactity as well as plant size; both large (overstory trees) and small (bryophyte and low statured herb) species sustained high mortality, whereas mid-sized taxa (robust herbs and shrubs) experienced high survivorship. Plant species richness in the toppled zone plots increased rapidly to ~25 species over the first five post-eruption years and then slowed. Plant cover was low (1-3%) from 2009 to 2011, but increased to 30-60% by 2016. At Cordon Caulle, 35-60 cm of pumiceous tephra annihilated most understory bryophytes, herbs and low shrubs (cover 0-5%), followed by slow increases of these lifeforms over the next five years. Overstory tree mortality was positively related to tephra thickness, but also varied by species. At an altitudinal gradient in Calbuco, 33-40 cm of dense, highly abrasive scoria tephra stripped epiphytes, foliage and fine-to-medium branch structures from trees. In this gradient tree survivorship was related to species’ resprouting capability and scoria damage to branches.