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Composites of Fire-Scar Chronologies from Southwestern U.S. Forests

These composite fire scar chronologies from 55 forest and woodland sites in Arizona, New Mexico, and northern Mexico (AD 1600-present) reveal regional synchrony. In the upper chart, each horizontal line represents the composite fire chronology from a different site, and the tick marks are the fire dates recorded by >10% fire-scarred trees (and >2 trees) within that site. The long tick marks are fire dates recorded by 10 or more sites in the southwestern network. Note that when adjacent chronologies have long tick marks for the same year, i.e., a regional fire event, this forms a continuous vertical line between the chronologies. Most of the sites were in ponderosa pine or mixed conifer forests, and the sampled areas typically ranged from ~10 to 100 ha, although a few sites exceeded 1000 ha. The average number of trees sampled per site was ~20, with a maximum of 56 trees. The line graph at the bottom shows the total number of sites recording fire dates each year. The labeled years with arrows were regional fire dates, i.e., fires occured in 10 or more sites across the network.