The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA

Citation: Zobel, D. B., and J. A. Antos. 2017. Community reorganization in forest understories buried by volcanic tephra.Ecosphere 8(12):e02045. 10. 1002/ecs2.2045 Abstract. Disturbance is a key factor contributing to community organization. Deposition of tephra (aerially transported volcanic ejecta) is a widespread disturbance of global relevance, but its effects on ecosystems have received limited attention. We studied forest understory community change for 30 yr following tephra deposition from the 1980 eruptions of Mount St. Helens (Washington State). Four oldgrowth, subalpine conifer stands had a wide range of initial damage and patterns of community re-development. We measured understory diversity, structure, and species composition and calculated relationships of plant cover with environment and cover of other plants. Overall, those communities that were altered greatly by tephra tended to converge with time on their pre-eruption characteristics; however, substantial divergence occurred in some situations. For example, moss cover failed to reach pre-eruption levels in all stands, whereas importance and diversity of woody plants sometimes greatly exceeded preeruption values. Plant-environment relationships that were significant before the eruption disappeared and did not re-develop. Smaller plants were more affected by environment than larger ones. Relationships before the eruption and also 30 yr after the eruption were primarily with other plant species, whereas relationships just after the eruption were with tephra depth and factors that modified its impact. Understory plant importance was usually lower beneath a tree canopy than in gaps, but there was little sign of interference from understory growth forms. Post-eruption soil disturbance usually increased understory plant importance, while woody debris sometimes decreased herb and tree seedling cover. Tephra deposition, which did not immediately kill canopy trees, differed from the disturbances usually studied (e.g., fire, windthrow, bark beetles). Even so, these lessons from our study should be widely applicable: Similar species may respond differently; minor, early environmental differences may induce major, long-term community change; successional trajectories may diverge from the pre-disturbance community; and secondary disturbances may modify successional trajectories.

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“…Tephra disturbance in our region has been extensive and frequent (Shipley and Sarna‐Wojcicki , Egan et al. ).…”

Section: Discussionmentioning

confidence: 96%

Community reorganization in forest understories buried by volcanic tephra

Zobel

Antos

2017

Ecosphere

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“…The Mazama tephra layer has previously been geochemically identified on the JEOL-JXA8600 electron microprobe at the Research Laboratory for Archaeology and the History of Art, University of Oxford (Egan et al, 2016). AMS radiocarbon dates were obtained for both cores as discussed in the previous work in Egan et al, (2016). Radiocarbon dating was carried out on bulk sediments as there were no identifiable macrofossils or macrocharcoal fragments.…”

Section: Stratigraphic Analyses and Radiocarbon Datingmentioning

confidence: 99%

“…Focussing on the aquatic effects of tephra deposition, this paper aims to enhance our understanding of tephra impacts. Egan et al, (2016) conducted a study on the terrestrial impacts of the tephra deposited by the Plinian eruption of Mount Mazama, Cascade Range, 7682-7584 cal yr BP (95.4% probability range) (Egan et al, 2015). Mount Mazama ejected nearly 50 km 3 of rhyodacitic magma into the atmosphere (ten times as much as the 1980 eruption of Mount St Helens), and deposited ash over an area of approximately 1.7x10 6 km 2 (Zdanowicz et al, 1999) in a predominantly north-easterly direction (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…Mount Mazama ejected nearly 50 km 3 of rhyodacitic magma into the atmosphere (ten times as much as the 1980 eruption of Mount St Helens), and deposited ash over an area of approximately 1.7x10 6 km 2 (Zdanowicz et al, 1999) in a predominantly north-easterly direction (Figure 1). Egan et al, (2016) reported a significant local impact on the terrestrial environment surrounding Moss Lake, Washington, with decreases in the open habitat vegetation. Building on the potential impacts from the Mazama tephra deposit here, we are now primarily interested in the nature and duration of the aquatic impacts, which Egan et al, (2016) did not address.…”

Section: Introductionmentioning

confidence: 99%

“…Egan et al, (2016) reported a significant local impact on the terrestrial environment surrounding Moss Lake, Washington, with decreases in the open habitat vegetation. Building on the potential impacts from the Mazama tephra deposit here, we are now primarily interested in the nature and duration of the aquatic impacts, which Egan et al, (2016) did not address. Egan et al, (2016) highlighted the importance of multiple cores as their analyses revealed a local terrestrial impact but no regional impact.…”

Section: Introductionmentioning

confidence: 99%

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Diatom-inferred aquatic impacts of the mid-Holocene eruption of Mount Mazama, Oregon, USA

2018

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High-resolution diatom stratigraphies from mid-Holocene sediments taken from fringe and central locations in Moss Lake, a small lake in the foothills of the Cascade Range, Washington, have been analyzed to investigate the impacts (and duration) of tephra deposition on the aquatic ecosystem. Up to 50 mm of tephra was deposited from the climactic eruption of Mount Mazama 7958–7795 cal yr BP, with coincident changes in the aquatic ecosystem. The diatom response from both cores indicates a change in habitat type following blanket tephra deposition, with a decline in tychoplanktonic Fragilaria brevistriata and Staurosira venter and epiphytic diatom taxa indicating a reduction in aquatic macrophyte abundance. Additionally, the central core shows an increase in tychoplanktonic Aulacoseira taxa, interpreted as a response to increased silica availability following tephra deposition. Partial redundancy analysis, however, provides only limited evidence of direct effects from the tephra deposition, and only from the central core, but significant effects from underlying environmental changes associated with climatic and lake development processes. The analyses highlight the importance of duplicate analyses (fringe and central cores) and vigorous statistical analyses for the robust evaluation of aquatic ecosystem change.

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Vegetation responses to past volcanic disturbances at the Araucaria araucana forest‐steppe ecotone in northern Patagonia

Moreno‐González

2022

Ecology and Evolution

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Volcanic eruptions play an important role in vegetation dynamics and its historical range of variability. However, large events are infrequent and eruptions with a significant imprint in today's vegetation occurred far in the past, limiting our understanding of ecological processes. Volcanoes in southern Andes have been active during the last 10 ka and support unique ecosystems such as the Araucaria – Nothofagus forest. Araucaria is an endangered species, with a fragmented distribution and well‐adapted to fire and volcanic disturbances. Yet, it was suggested that volcanism might have increased the fragmentation. Through the use of pollen and tephra analysis from a sedimentary record, this paleoecological study aims to provide an insight into the vegetation responses to past volcanic disturbances, to assess the role of volcanic disturbance on the vegetation dynamics and to determine if the current fragmentation has been caused by volcanism. Results show that during the last 9 kyr, 39 tephra falls buried the vegetation around Lake Relem, more frequently between 4 and 2 ka. The pollen percentage indicates that the vegetation changed after small tephra fall but seldom caused significant changes. However, the large eruption of Sollipulli volcano (~3 ka) changed the environmental conditions affecting severely the vegetation. Ephedra dominated the early successional stage, perhaps facilitating Nothofagus recovering after ~500 years. Slight increase of Araucaria and Nothofagus obliqua ‐type pollen percentages suggests that forest resisted without permanent changes and recovered relatively fast after the large eruption, perhaps because of sparse biological legacies distributed in the landscape. In the study area, the relative stability of Araucaria pollen after several tephra fall suggests no change in its past distribution at the current forest‐steppe ecotone, thus not affecting its current conservation status. Perhaps, random factors, the colonization patterns of the high elevations in the Andes after deglaciation and topography might play a more important role than previously thought.

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The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA

Cited by 18 publications

References 94 publications

Community reorganization in forest understories buried by volcanic tephra

Community reorganization in forest understories buried by volcanic tephra

Diatom-inferred aquatic impacts of the mid-Holocene eruption of Mount Mazama, Oregon, USA

Vegetation responses to past volcanic disturbances at the Araucaria araucana forest‐steppe ecotone in northern Patagonia

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