Not all forests, just ones in drier/hotter regions (Canada's boreal forests don't regularly burn, for example). The forests in the Western USA were purposefull

Not all forests, just ones in drier/hotter regions (Canada's boreal forests don't regularly burn, for example). The forests in the Western USA were purposefully burnt by the inhabitants for thousands of years prior to the ~1950s so I believe we don't know how much or if they relied on fire prior to man inhabiting the Americas.