Fires are widespread in prairies globally. Fire often perpetuates grasslands by counteracting tree encroachment, yet there is often little record of this fire preserved in the grasslands. Fortunately adjacent woodlands can contain long-lived tree species capable of recording fire occurrence via cambial scars. These fire scars can be dated dendrochronologically to determine the past occurrence of fire in the adjacent grasslands. The Palouse prairie of eastern Washington and adjacent Idaho was a mixed grass and shrub biome with isolated trees before 95% of it was converted to agriculture.
Early ecologists argued that fire was not important in maintaining the Palouse prairie because relatively moist conditions there were conducive to rapid decomposition of fuel and lightning is relatively uncommon. However, it has been suggested more recently that fires were historically frequent there because the rolling terrain is conducive to fire spread, humans were likely igniting fires in the past, and summers are long and dry. Strong evidence for or against the role of fire could be obtained from adjacent forests. The eastern edge of the Palouse prairie abuts mixed-conifer forest where fire scarred ponderosa pine trees are common. Understanding the past role of fire on the fringe of the Palouse prairie and in the western-most forests of the Rocky Mountains will provide guidance for how to manage these landscapes into the future.
Preliminary analysis has revealed forested sites at the edge of the Palouse burned frequently (every 6±4 years) between 1650 and 1900, suggesting that fire was important in maintaining the Palouse Prairie in the past.