1200 years of fire and vegetation history in the Willamette Valley, Oregon and Washington, reconstructed using high-resolution macroscopic charcoal and pollen analysis

a r t i c l e i n f o Keywords: Macroscopic charcoal Fire Paleoecology Pollen Anthropogenic burning CharAnalysis Euro-American settlement Willamette Valley Oregon Washington High-resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the Willamette Valley for the last 1200 years. 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 200–300 years 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. The current vegetation of the Willamette Valley is vastly different from that seen by 19th-century Euro-American explorers and settlers. Survey notes from the General Land Office (GLO) indicate that pre-settlement vegetation (ca. AD 1850) was a complex mosaic of Quercus (oak) savanna and woodland, grasslands ('prairie' ranging from moist to dry), coniferous upland forest, and extensive riparian forests remnants of these ecosystems remain, precariously perched between rapidly expanding urban and agricultural areas (Hulse et al., 2002). Numerous studies have shown that over the past ca. 150 years, shrubs and trees have established in former wet and upland prairie, and conifers have come to dominate former oak savanna and woodland The removal of fire, both naturally-and human-ignited, from these ecosystems is partially, if not entirely, …