paul hessburg: the 1910 big burn. it burned 3 million acres across three states, killed 87 people, mostly firefighters. and our awareness and our whole consciousness about fire pivoted in that moment. reporter: this is a picture of tragedy, a tragedy that happens year after year in our great american forest areas-- fire. fire became public enemy number one. and wildfires were to be put out at all cost. steve pyne: and at that point, we almost militarized firefighting. kyle dickman: we were really good at it. firefighters could put out 99% of fires before they grew bigger than an acre. paul hessburg: and from about 1935 to about 1985, you see not much fire burning. and it made our fire suppression look great. steve pyne: and that was a very poor judgment. well, they completely misjudged the character of the overall fire scene. paul hessburg: what's happened since the exclusion of fire is forests have gotten denser. the forests of today look nothing like they did in the 1930s. there are 10 times even more trees than tha