26 Feb 2008, 5:57pm
Fire History
by admin

Are Lightning Fires Unnatural? A Comparison of Aboriginal and Lightning Ignition Rates in the United States

Kay, Charles E. Are Lightning Fires Unnatural? A Comparison of Aboriginal and Lightning Ignition Rates in the United States. 2007. in R.E. Masters and K.E.M. Galley (eds.) Proceedings of the 23rd Tall Timbers Fire Ecology Conference: Fire in Grassland and Shrubland Ecosystems, pp 16-28. Tall Timbers Research Station, Tallahassee, FL.

Full text [here]

Selected excerpts:


It is now widely acknowledged that frequent, low-intensity fires once structured many plant communities. Despite an abundance of ethnographic evidence, however, as well as a growing body of ecological data, many professionals still tend to minimize the importance of aboriginal burning compared to that of lightning-caused fires. Based on fire occurrence data (1970–2002) provided by the National Interagency Fire Center, I calculated the number of lightning fires/million acres (400,000 ha) per year for every national forest in the United States. Those values range from a low of <1 lightning-caused fire/400,000 ha per year for eastern deciduous forests, to a high of 158 lightning-caused fires/400,000 ha per year in western pine forests. Those data can then be compared with potential aboriginal ignition rates based on estimates of native populations and the number of fires set by each individual per year. Using the lowest published estimate of native people in the United States and Canada prior to European influences (2 million) and assuming that each individual started only 1 fire per year—potential aboriginal ignition rates were 2.7–350 times greater than current lightning ignition rates. Using more realistic estimates of native populations, as well as the number of fires each person started per year, potential aboriginal ignition rates were 270–35,000 times greater than known lightning ignition rates. Thus, lightning-caused fires may have been largely irrelevant for at least the last 10,000 years. Instead, the dominant ecological force likely has been aboriginal burning.

keywords: aboriginal burning, Indian burning, lightning-caused fires, lightning-fire ignition rates, potential aboriginal ignition rates.


It is now widely acknowledged that frequent, low intensity fires once structured many plant communities in the United States. Anderson (2005), Stewart (1956, 1963, 2002), Zybach (2003), Lewis (1973, 1977, 1985), Pyne (1982, 1993, 1994, 1995), and others. (Blackburn and Anderson 1993, Kay and Simmons 2002, Carloni 2005, Gassaway 2005) contend that, historically, most fires were set by native people to manage their environment. Vale (2002), Baker (2002), and their colleagues (Houston 1973, Loope and Gruell 1973), however, maintain that the case for aboriginal burning has been overstated and that most fires, historically, were started by lightning. According to Baker (2002:41–42), “Ignitions by Indians were… probably numerically insignificant relative to lightning ignitions… [and] Indians were a small part of a large Rocky Mountain wilderness, with a fire regime… essentially free of human influence for millennia.” However, neither Vale (2002) nor Baker (2002) presented data on actual lightning ignition rates nor compared known lightning ignition rates with potential aboriginal ignition rates. In this paper, I present data on lightning-fire ignition rates for every national forest in the contiguous United States and then compare those figures with potential aboriginal ignition rates based on hypothetical estimates of native populations and the number of fires accidentally and purposefully set by each individual per year.


The National Interagency Fire Center in Boise, Idaho, provided data on the number of known lightning-caused fires that occurred on individual national forest from 1970 to 2002. Based on the area of each forest, I then calculated lightning-fire ignition rates/million acres (400,000 ha) per year (Table 1). Those data range from a low of <1 fire/400,000 ha per year to 158 fires/400,000 ha per year on the Plumas National Forest in California. Ponderosa pine (Pinus ponderosa)-dominated forests in Arizona and New Mexico also have high lightning-fire ignition rates but, surprisingly, most national forests have relatively low lightning-fire ignition rates-this is especially true of national forests in the East (Figures 1, 2). Even the majority of western national forests, though, have relatively low lightning ignition rates (Figures 1, 2). Several national forests in Montana, Wyoming, and Colorado have <10 lightning-caused fires/400,000 ha per year (Table 1). National forests also have higher lightning-fire ignition rates than surrounding, lower-elevation, Bureau of Land Management (BLM), state, and private land (Barrows 1978). When those data are included, the mean lightning-fire ignition rate on all lands in the western United States is approximately 19 fires/400,000 ha per year (Table 2).

These data then do not support the idea that the United States, or even the West, is awash in lightning started fires. Popular misconceptions regarding the frequency of lightning fires may be due to media coverage during recent extreme fire seasons, as well as the fact that many fire-history studies have been done on the few national forests in California, Arizona, and New Mexico that have relatively high lightning-fire ignition rates.


Any estimate of aboriginal ignition rates must consider at least three factors—the number of landscape fires started inadvertently per person per year, the number of fires purposefully set per person per year, and the number of people. Unfortunately, how many people there were in the Americas prior to Columbus’ landfall is not a settled issue. In fact, the entire subject is exceedingly contentious and highly charged, as it impinges directly on various national creation beliefs, charges of genocide by remaining indigenous inhabitants, and core environmental values, such as the idea of wilderness (Stannard 1992, 1998; Loewen 1995; Churchill 1997; Kay and Simmons 2002; Vale 2002; Mann 2005). …

… The only certainty is that Europeans have consistently underestimated the antiquity of aboriginal occupation, as well as the political and technical sophistication of America’s original inhabitants (Mann 2005).

To be conservative in my evaluation of potential aboriginal ignition rates, I started with the lowest, published and commonly accepted estimate that I could find, namely 2 million native people in the continental United States and Canada ca. 1491 (Mann 2005). As there are approximately 1.5 billion ha north of Mexico, this yields a density estimate of 428 people/400,000 ha. Assuming there were only 500,000 natives in that area, as Alroy (2001) calculated for the end of the Pleistocene, then the density estimate is 107 people/400,000 ha. Both are seemingly insignificant figures.

Escaped Campfires—Inadvertent Landscape Burning

… no evidence exists that native people ever purposefully extinguished their heating or cooking fires. Most likely, they simply walked away and left their campfires burning.

In a very extensive search of the literature, I discovered almost no reference that natives anywhere carefully extinguished fires… Everywhere that man traveled, he made campfires and left them to ignite any and all vegetation in the vicinity [Stewart 1956:118].

… Similarly, anthropologists who work with modern day hunter–gatherers living in South America, Australia, and Africa report that their subjects never extinguish heating or cooking fires unless under duress by Europeans (Jim O’Connell, University of Utah, personal communication; William Preston, California Polytechnic State University, personal communication; Richard Chacon, Winthrop University, personal communication).

Peter Fidler, who traveled with a band of Piegan natives in what is today central and southern Alberta during the winter of 1792–1793, reported how aboriginal attitudes toward fire differed from those of Europeans:

Tents [of Piegan] joined us that was tenting 3/4 mile to the Eastward of us. They did not put out their fire when they left it, which spread amongst the dry grass and ran with great velocity and burnt with very great fury, which enlightened the night like day, and appeared awfully grand. The wind being fresh drove it at a great distance in a little while [Haig 1992:58].

This observation was recorded on 18 January, a time of year when lightning-started fires are nonexistent on the northern Great Plains (Higgins 1984).

So, to begin with a simple and conservative assumption that there was only 1 escaped campfire/year per adult aboriginal inhabitant, and using the previous estimate of 428 native people/400,000 ha, this produces an estimate of 428 escaped fires/400,000 ha per year, which is 2.7 times the highest known lightning ignition rate in the West or 350 times the lightning ignition rate for national forests in the East (Table 1).

If, on the other hand, we assume there were 20 million native inhabitants, possibly a more realistic figure (Dobyns 1983, Mann 2005), then the estimated escaped-camp-fire ignition rate is 27 times higher than the highest known lightning ignition rate and 3,500 times higher than the lightning ignition rate in much of the eastern United States.

If we assume 10 escaped campfires/year per aboriginal inhabitant, instead of 1, then the accidental ignition rate is 270 times the highest lightning started rate and 35,000 times the lightning-fire ignition rate in the East. …

Baker (2002:41) dismissed aboriginal burning as a significant ecological force, in part because he contended that “only about 30,000″ native people inhabited the northern Rockies. Baker did not define what he considered the northern Rockies but if we assume this includes one-half of Colorado, one-half of Montana, one-half of Wyoming, and one-third each of Idaho and Utah, we have an area of 610,000 km2 (235,000 mi2) or 1 aboriginal inhabitant/19 km2 (7.3 mi2). Again, a seemingly insignificant figure. A number, however, that translates to 212 people/400,000 ha. The mean lightning ignition rate for national forests in the northern Rockies, though, is only 17.6 fires/400,000 ha per year (Table 1). Assuming only 1 escaped campfire/aboriginal person per year, the accidental ignition rate is still 12 times the lightning ignition rate. Any other assumptions as to the number of escaped campfires only put more fire on the landscape. Thus, this hypothetical example does not support Baker’s (2002:41) conclusions that aboriginal fires were “insignificant” or that the Rockies were a wilderness untouched by the hand of man. …

Finally, despite an extremely successful anti-fire public relations campaign, fire bans, and other measures, including closing entire national forests during high fire danger, 49% of the fires recorded in the National Forest System from 1940 to 2000 were caused by humans, not by lightning-and those human-set fires accounted for 57% of the area burned (Stephens 2005).

Purposeful Burning—Management-Set Fires

Although there is little doubt that Native Americans used fire to purposefully modify their environment (Stewart 1963, 2002; Lewis 1973, 1977, 1985; Anderson 2005), ethnographers have failed to record the number of fires set/person per year. The only data that I have been able to locate on this subject come from Australia where, in a few locations, aboriginal people still use fire to purposefully modify the vegetation as their ancestors are thought to have done for the last 45,000–50,000 years (Hallam 1975, Lewis 1989, Flannery 1994, Fensham 1997, Russell-Smith et al. 1997, Bowman 1998, Bowman et al. 2004, Vigilante and Bowman 2004). In Australia, most of the aboriginal-set management fires are started by men and each individual sets 100 or more fires/year, mostly at the end of the wet season and the beginning of the dry season-a time when lightning-fires are rare to nonexistent.

This creates a vegetation mosaic that not only is more productive for the indigenous inhabitants but which also prevents large-scale, high-intensity, lightning-caused fires during the height of the dry season. Aboriginal-managed areas have also been shown to have higher plant and animal biodiversity than adjacent national parks, where lightning-caused fires are allowed to burn unchecked but where aboriginal burning is prohibited (Yibarbuk et al. 2001, Fraser et al. 2003).

So if we conservatively assume that each Native American purposefully set only 1 fire/person per year, and that there were only 2 million native people north of Mexico, the aboriginal burning rate would have been 2.7–350 times greater than known lightning ignition rates (Table 1). If 10 fires/person per year were set, possibly a more realistic assumption (Boyd, T., 1986; Turner 1991; Gottesfeld 1994; Boyd, R., 1999; Anderson 2005), the aboriginal burning rate would have been 27–3,500 times greater than known lightning ignition rates. If there were 20 million Native Americans, instead of 2 million, that would add another order of magnitude to the estimated rate of purposefully set fires.

Finally, if estimates of accidentally started aboriginal fires are combined with estimates of purposefully set management fires, the overall aboriginal burning rate would have been 2–5 orders of magnitude greater than known lightning ignition rates.

Even if we assume there were no more than 500,000 native people in the United States and Canada, aboriginal ignition rates would still have overshadowed lightning fires. Thus, there have been more than enough people in the Americas for the past 10,000 or so years to completely alter fire regimes and vegetation patterns.

Moreover, widespread aboriginal burning, by consuming fuels and creating patches of burned and unburned vegetation, limited the spread and extent of any lightning fires that may have started, similar to what has been documented in Australia (Kay 1998, 2000). This would suggest that lightning-caused fires have been largely irrelevant in structuring plant communities throughout many areas in North America. It also turns out that it does not require very many native people to completely alter fire regimes because lightning ignition rates were so low and aboriginal ignition rates so high. [emphasis W.I.S.E.]

  • Colloquia

  • Commentary and News

  • Contact

  • Topics

  • Archives

  • Recent Posts

  • Meta