What are trees made out of? If you had asked me yesterday, I would have guessed that trees absorb raw materials from the ground through their roots, and use them to build new branches and roots as the tree grows. Or, perhaps trees are constructed by hardworking but underpaid gnomes and fairies during the night.
As it happens, that's not the case. Although roots take up a small amount of important nutrients, the majority of the mass of a tree is created from carbon dioxide absorbed from the air by the tree's leaves. That's right. It sounds crazy, but trees are mostly made out of air, and fairies aren't even involved.
When you burn wood, you're just dumping all that carbon dioxide back into the air where it originally came from. Don't do that. It annoys the fairies.