The effects of fire and tephra deposition on forest vegetation in the Central Cascades, Oregon
2011
Long, Colin J. | Power, Mitchell J. | Bartlein, Patrick J.
High-resolution charcoal and pollen analyses were used to reconstruct a 12,000-yr-long fire and vegetation history of the Tumalo Lake watershed and to examine the short-term effects that tephra deposition have on forest composition and fire regime. The record suggests that, from 12,000 to 9200calyr BP, the watershed was dominated by an open Pinus forest with Artemisia as a common understory species. Fire episodes occurred on average every 115yr. Beginning around 9200calyr BP, and continuing to the present, Abies became more common while Artemisia declined, suggesting the development of a closed forest structure and a decrease in the frequency of fire episodes, occurring on average every 160yr. High-resolution pollen analyses before and after the emplacement of three distinct tephra deposits in the watershed suggest that nonarboreal species were most affected by tephra events and that recovery of the vegetation community to previous conditions took between 40 and 100yr. Changes in forest composition were not associated with tephra depositional events or changes in fire-episode frequency, implying that the regional climate is the more important control on long-term forest composition and structure of the vegetation in the Cascade Range.
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