What are the main causes of forest fires?

There are seven: Those caused by smokers' matches or by burning tobacco in any form; campfires; debris burning-fires which are originally set for clearing land or disposing of rubbish, stubble, and such and which get beyond control; incendiary, which are deliberately started with the intention of burning over the land or damaging property owned by someone else; lightning; lumbering; fires resulting from maintenance of right-of-ways or construction or operation of railroads.