From his website:

All of our pieces are created from resawn hardwood beams salvaged from dismantled buildings across the country. From a barn outside of Kutztown, Pennsylvania to a tobacco warehouse in eastern Tennessee, to a textile mill in Massachusetts, each beam has a story, and carries its history in its grain.
Close to a billion board feet of wood are removed from buildings in the US every year. By reusing this material we reduce the impact on our landfills, eliminate the need to harvest trees, and are reminded of the simple beauty inherent in old wood.
We use Ash as our primary species.  An indigenous hardwood, ash has a unique blend of durability, stability and warmth.
Red and white oak and maple are also available for special orders at an additional cost, and from time to time we are fortunate to find walnut and cherry as well.