(Man-made) smoke gets in your eyes
In his book Forgotten Fires: Native Americans and the Transient Wilderness, anthropologist Omer C. Stewart argues persuasively, using documentation and physical evidence, that for thousands of years, residents of this continent have regularly used fire to burn grasslands and forest understory for a variety of reasons. He quotes the journals of 18th century Spanish explorers in Southern California, who complain frequently of lack of grazing for their animals because the grass had been burned by "the heathen."
Stewart contends that, because human beings in North America have used fire to shape their environment for thousands of years, we must consider man-made fire to be a natural ecological force.
Stewart's book is essential reading for anyone who wants to understand the effects of fire on the environment, and for anyone in a position to influence government policy toward fire.