The theory was that forests should be kept as pristine as possible and, in particular, protected from fire. The attitude was that old trees were sacred and underbrush provided wild life habitat. Forest fire detection and firefighting techniques evolved to support the theory. What happened was that unthinned woodland giants choked off light to younger growth, which died and became deep tinder on the forest floor. That tinder is now feeding the walls of flames that are devouring great parts of the West.
Fire is a natural cycle in forests.
Low-fuel forest fires do not destroy big trees and only temporarily displace wildlife. Fire is needed to melt the resin in pine cones to release seeds for natural reforestation. But the high-fuel fires now burning destroy everything, leaving barren land. Environmentalists' insistence on zero cutting was prompted by past clear-cutting practices in the lumber and paper industries. A clear cut in the middle of a beautiful forest is like an open wound.