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Abstract: High-resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the Willamette Valley for the last 1200years. Presented in this paper are three new paleoecological reconstructions from Lake Oswego, Porter Lake, and Warner Lake, Oregon, and portions of previous reconstructions from Battle Ground Lake, Washington, and Beaver Lake, Oregon. The reconstructions show that prior to Euro-American settlement vegetation and fire regimes were influenced by a combination of natural and anthropogenic factors. Battle Ground Lake shows a stronger influence from climate, while Lake Oswego, Beaver Lake, Porter Lake, and Warner Lake were more controlled by human activity. However, human-set fires were also modulated by regional climate variability during the Medieval Climate Anomaly and the Little Ice Age. Fire reconstructions from Battle Ground Lake, Lake Oswego, Beaver Lake, and Porter Lake imply that fires were infrequent in the Willamette Valley 200–300years prior to Euro-American settlement. The decline of Native American populations due to introduced disease may have led to this reduction in fire activity. The prehistoric record from Warner Lake, however, indicates that fires in the foothills of the Cascade Range were more frequent than on the valley floor, at least until ca. AD 1800. The historic portions of the reconstructions indicate that Euro-American land clearance for agriculture and logging produced the most dramatic shifts in vegetation and fire regimes. All five records indicate that few fires in the Willamette Valley have occurred since ca. AD 1930, and fires today are predominantly grass fires. [ABSTRACT FROM AUTHOR]

Fire has been an important Earth System phenomenon for millions of years and our ability to understand its role in geologic history relies upon robust and unequivocal paleofire archives. Charcoal particles preserved in sedimentary deposits form the primary basis of our understanding of fire's variability on geologic timescales as well as its role in the emergence of plant physiology, ecosystems, and biogeographic configurations. An intriguing aspect of global Cenozoic fire history is the surge in fire activity that is thought to have occurred in the late Neogene (beginning ca. 7 Ma) and indicates that modern biogeography, ecology, and plant physiology was born out of the ashes of an extremely fiery period in Earth's history. The late Neogene fire surge is primarily inferred from charcoal fluxes to sediment records in the North Pacific. In this paper, we revisit these data and show that they are unlikely to reflect an increase in fire activity alone. Rather, these charcoal fluxes likely also reflect an anomalous late Neogene increase in the amount of terrigenous material (and charcoal) supplied to marine sediment records and/or an inflation of late Neogene charcoal flux measurements (and sedimentation rates) resulting from the incompleteness of older stratigraphic sections. These results highlight the importance of accounting for sediment preservation biases when interpreting long term paleoenvironmental records and suggest charcoal fluxes in the North Pacific do not provide conclusive evidence that fire activity increased in the late Neogene. • Late Neogene (~7 Ma) surge in marine charcoal fluxes is unlikely to reflect fire alone. • Preservation biases likely inflate the charcoal fluxes, exaggerating fire activity. • The Sadler effect is present in the marine charcoal dataset. • Marine charcoal fluxes are inconclusive evidence for a late Neogene fire surge. [ABSTRACT FROM AUTHOR]