PLATE 9 Composites of fire-scar chronologies for 55 forest stands in Arizona, New Mexico, and northern Sonora, Mexico from the years 1600 to 2000, as reconstructed from tree-ring analyses of fire-scarred trees. The red and yellow vertical tick marks indicate the fire dates recorded by the fire-scarred trees sampled in each stand. The red tick marks represent regional fire years that were recorded by fire scarred trees in 10 or more of the sampled stands. Many of these regional fire years occurred during droughts that were probably associated with La Niña events. Note the very striking decrease in sites recording fires more recently than circa 1890, coinciding with the introduction of large numbers of livestock and organized suppression of fires by government agencies (Swetnam et al., 1999). Major changes in anthropogenic land use affect the frequency of fires associated with droughts.

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