Can soil phytolith analysis and charcoal be used as indicators of historic fire in the pinyon-juniper and sagebrush steppe ecosystem types of the Great Basin Desert,USA?

Wildland fire intensity and area are increasing across the Intermountain West, USA, in a variety of ecosystem types including the pinyon-juniper woodlands and sagebrush steppe of the Great Basin Desert. Unfortunately, we do not know if there were historic analogues for these high-intensity stand-replacing fires because of the lack of fire scars that record evidence of them. Soil-charcoal and phytolith analyses have been successfully employed in other regions to garner information about fire regimes through the Holocene. We studied the utility of these methodologies and related taphonomic issues in soils in the Great Basin Desert. Our results showed that both microscopic charcoal and burned phytoliths can be found in soils with radiocarbon ages from modern to late Holocene. Microscopic charcoal abundance was more useful than size class as an indicator of recent local fire. Its abundance declined rapidly and remained low at 2.8 to 4.8 km from the edge of the fire. A Burned Phytolith Index shared a similar pattern starting at 0.4 km from the fire edge. Both proxies declined in abundance with depth in the soil at recent burn sites while remaining constant in unburned sites. We were unable to detect a signal for a known historic fire, however, this may have been a result of sample depth. Our results indicate that soil-charcoal and phytolith analysis can be used to examine questions about historical fires in these two ecosystems of the Great Basin Desert.