Investigating the fire regimes of the United States pre- and post-settlement by Euro-americans can give important clues to current and future fire activity for the region. It can also help explain current fire behavior, and help inform future management decisions.

Fire regimes can be described by creating fire histories: the actual record of fires for a particular geographic area. A variety of techniques can be used to create fire histories including building chronologies of fire scarred trees, forest age and stand structure reconstructions using dendrochronology, repeat photographs, historical writings, and early land survey records.

The figures below illustrate some key characteristics of pre- and post-settlement fire regimes for the southwestern United States, as derived from fire histories.  Figure 1 shows a wide distribution of fires throughout the region for the 2002 fire season. Figure 2 also shows a wide distribution of fires throughout the region for the 1748 fire season as recorded by fire scar chronologies for the time period 1600-present. Figure 3 indicates that large, regional fire years were not uncommon for the pre-settlement era. In fact, long periods of time without fire are an anomaly for many forest types in the region. However, fire severity has increased in many forest types in the modern era, at least in part due to the high forest fuel load resulting from fire suppression starting at the turn of the last century.

2002

1748

Fig. 1.   Fires greater than 100 acres for the year 2003, as of July 29, 2003. Data from USFS Region 3 website. Shaded relief map from USGS EROS Data Center.

Fig. 2.   Fire history sites with 2 or more trees recording fires per site for 1748.
From Swetnam, T. W., C. D. Allen, and J. L. Betancourt. 1999. Applied historical ecology: Using the past to manage for the future. Ecological Applications 9(4):1189-1206.

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Timeline of Sites recording Fires in the Southwestern United States.

Fig. 3.  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 > 1 tree ) within that site. The long tick marks are fire dates recorded by >= 10 sites in the southwestern network. Note the 1748 fire year mapped in the preceding figure. Figure and text from Swetnam, T. W., C. D. Allen, and J. L. Betancourt. 1999. Applied historical ecology: Using the past to manage for the future.Ecological Applications 9(4):1189-1206.

For questions contact Merrick Richmond at merrick@ltrr.arizona.edu