What happens if forest fire ignitions are not suppressed? It’s a tough experiment to perform, but some old Forest Service data may help answer. In 1923, the Forest Service published an analysis of fires in 12 California national forests (excepting southern California) that ignited between 1911 and 1920. The data include suppression costs, which are a good proxy for suppression effort. Recall that 1910 was the “Great Fire,” which ushered in the era of Forest Service fire suppression. In 1911 fire suppression was almost non-existent with costs on the 12 forests totaling $18,746. That’s $450,000 in today’s dollars. Compare to 2015’s $500 million spent by the Forest Service suppressing fires in California (even more in 2017), and the numbers show the Forest Service puts about 1,000 times more effort into suppressing fires today than it did in 1911. In 1911 there were no air tankers, no fire engines, and few roads into the national forests. In sum, 1911 is a pretty good proxy for what happens when ignitions are not suppressed.
So what did happen to ignitions in 1911? Click on the table above: 70% remained smaller than 300 acres, while 30% exceeded 300 acres. [“C” fires are those greater than 300 acres]