Our forests are exposed to destruction by many enemies, the worst of which is fire. From 8,000,000 to 12,000,000 acres of forest lands annually are burned over by destructive fires. These fires are started in many different ways. They may be caused by sparks or hot ashes from a locomotive. Lightning strikes in many forests every summer, particularly those of the Western States, and ignites many trees. In the South people sometimes set fires in order to improve the grazing. Settlers and farmers who are clearing land often start big brush fires that get out of their control.