Is there a way to treat wood siding that is safe to burn?
I lived in a house growing up that had some diagonal board &amp; batten siding that had gone to a shade of grey like an untreated cedar fence, and I know it wasn't painted, but it's possible it was stained.

But I'd agree with DA01 -- there's lots of types of 'green building', and I'd rather go with long-lasting and locally produced (to minimize shipping) products.  If you take care of your wood siding, it reach its end of life until after you're gone.  (my house is 80+ years old, and although the sills have been replaced, the siding is still original)

If it were me, building today, I'd probably not go with wood, and look at some of the fiber cement board products, particularly if it's produced nearby.