Works both ways.
Without air tankers, fire engines, Hot Shot crews, chainsaws, STEEL tools...and the pulaski had yet to be invented... they didn't even try to put a dent in natural fires, which could burn for months. And such fires had burned regularly, since the beginnings of dry land vegetation and the invention of lightening.
What ever burning they added, also subracted from acreage available for natural burns.
Oh, well; like all other "unnatural man made events", since these types seem to believe that Man is not a part of nature, natural fires are great; man made fires bad, as in "beaver dam good; stock pond evil".
. . . which there wouldn't have been any of in the first place without "greenhouse gases" (they call it "the greenhouse effect for a reason, ya know!) . . .