In my neck of the woods it’s not necessarily natural.
Most likely it’s someone thinking he or she can control any type of fire
Yard burn on a windy day
Yard burn left going after ya went to bed
Cigarette out the window
Yard burn during yard burn ban season
Mowing a lawn which has long since gone brown
Chain sawing without a fire extinguisher
Welding without a fire extinguisher
Dragging a muffler you’re too cheap to fix
Wood stove without a spark diffuser
Fireplace ashes in a paper bag
Cheap lazy halfwit guy who thought to himself
Why cut that brush down
I’ll just singe it in place
Yeah that’s the ticket
One was caused by a homeless guy throwing a lit roll of toilet paper at his DAWG
To quote Yul Bryner
etc, etc, etc

and
too many lose the total material substance of their lives
plus pets
TOTAL