Bark shingles are making a comeback; they're not only salvaged from logging (otherwise they'd be burned, mulched, or left to rot), they're low maintenance, contain no chemicals, and are a good insulator. Bark shingled homes (this is the whole home, not the roof) date from 1895. The main source of bark was the chestnut tree; some of those homes are still in use today. 'Course after the chestnut blight, that source was lost, and bark houses were no longer built. This material is more expensive up front, but it's maintenance-free.
I came across the article, Nature's Shingles in The Christian Science Monitor (the December 20, 2009 print issue). Link: Bark houses are built with nature’s shingles / The Christian Science Monitor - CSMonitor.com