Yes, it is April Fools Day but I am serious.  Trees are made of air.  Think about it.  What happens when they are burned?  You are left with a small pile of ash.  So where did the rest of the tree go?  When the tree ‘is burned, in the flaming heat is released the flaming heat of the sun which was bound in to convert air into the tree’.  These words are from Richard Feynman, who explains it much better than me.  Watch him on Youtube.

Sources:

Max Tegmark, Our Mathematical Universe, Penguin Books Ltd, 2014.

National Public Radio blog