Often times it is people burning leaves on windy days or young kids who think it is funny, not thinking ahead to the danger it poses. Sometimes it turns out to be someone on the volunteer fire department crew that loves fighting fires. There was a guy in Florida, that went around starting fires, just so he could fight them. He went to jail for a few years over that one. Many times it can be a piece of glass that the sun hits and mix in dry leaves and it equals fire.