In fact, fire ecologists say that far more land burned each year during the 1800s and earlier, than in recent years. In the preindustrial era, from 1500 to 1800, an average of 145 million acres burned every year nationwide — about 10 times more than the nation’s recent annual burns. In the West, Arno estimates that 18 to 25 million acres burned each year, as recently as the 1800s.
https://www.hcn.org/issues/251/13986