Southwest fire history chart. Fifty-five fire-scar chronologies for different forest sites in 27 mountain ranges of the southwestern United States. The yellow and red tick marks on each time series are fire dates recorded by fire-scarred trees. At least 10 fire-scarred trees were sampled in each site, and the tree rings and fire scars were dated by dendrochronology methods. Each time series is a composite of the fires recorded by at least two trees in each site. The red tick marks show regional fire years defined by 10 or more of the 55 chronologies (sites) recording the fire date. The yellow tick marks show the other fire dates recorded in nine or fewer sites. The step-line graph at the bottom is a summation of the number of sites recording the fire dates; the regional fire years are in red and are labeled. The decrease in recorded fires after ca. 1900, reflecting livestock grazing affecting fine fuels, and subsequent fire suppression by government agencies.