Bloomberg: Wood is becoming a hot commodity in a new low-carbon world. Power companies are burning trees because they’re renewable and can be cheaper than coal. Wood needs no permit to release carbon dioxide, a greenhouse gas blamed for global warming. Vattenfall AB of Sweden, Germany’s RWE AG and American Electric Power Inc. of Ohio, the biggest coal-burner in the U.S., have switched a few plants over to wood and more are planned. So far that hasn’t driven up paper prices or strained …