Wave of fire: an anthropogenic signal in historical fire regimes across central Pennsylvania, USA

Increasingly detailed records of long-term fire regime characteristics are needed to test ecological concepts and inform natural resource management and policymaking. We reconstructed and analyzed twelve 350+ yr-long fire scar records developed from 2612 tree-ring dated fire scars on 432 living and dead pine (Pinus pungens, Pinus rigida, Pinus resinosa, Pinus echinata) trees from across central Pennsylvania. We used multiple spatial and time series analysis methods to quantify fire regime characteristics (frequency, seasonality, percentages of trees scarred, extent) and fire-climate-human associations. Prior to the 20th-century fire suppression, fire regimes at the majority of sites consisted of frequent, low-to-moderate severity, dormant season fires. Fires were often regionally synchronous when preceded by significantly dry years. Using documentary archives, we provide the first description of a "wave of fire"-an anthropogenic signal in fire frequency that progressively moved across the region. This "wave of fire" reflects a changing progression of anthropogenic fire regimes from Native American occupation and depopulation, to Euro-American settlement, to industrialization and declining fire use up to the 20th century era of fire suppression. The wave of fire provides a new perspective on historical and modern fire regime dynamics and identifies socio-ecological impacts since North American colonization. Because the anthropogenic wave of fire exists at sites across North America, we emphasize the need for a broader determination of its geographic prevalence and variability as such determinations could influence historical ecology interpretations and perspectives on past and future roles of humans in managing ecosystems with fire.