Who Stopped the Fire? Fire Scars from Ponderosa Pines in the Great Basin and Mojave Deserts Indicate Reduced Wildfire Frequency Even Without Active Fire Suppression

Southwestern ponderosa pine forests have experienced reduced fire frequency since Euro-American settlement generally because of successful fire suppression policies. We report here on fire history records from ponderosa pine stands located in the Great Basin and Mojave Deserts. Fire-scarred ponderosa pines were sampled by taking partial cross-sections and wood increment cores. Maximum age of ponderosa pines at the study areas exceeded 800 years, and sampled trees were often older than 500 years, so that the site tree-ring chronology covered the past few centuries. Crossdating revealed both extreme sensitivity and highly synchronous patterns. Fire statistics were calculated for the periods during which at least 10 of the crossdated trees had been scarred and were recording fire. During the recorder period, the longest fire-free intervals occurred in the past two centuries, even without active fire suppression. Overall there was reduced fire frequency from the late 19th Century to present compared to the previous three centuries. Because there is no record of active fire management in the study areas, this finding points to a need for greater spatial coverage in fire history information, even for species that have been actively studied in other environments.