Owners of forestland in the Pacific NW could benefit more under a national carbon offsets system, as trees common to the region store more carbon per acre than East Coast species. Pictured: Douglas firs in an Oregon forest.Courtesy Ecotrust's sbeebe via FlickrThough most people probably think of national parks when they think of forests, more than half of the 750 million acres of forestland in the United States is actually privately owned, much of it by individuals and families, according to the American Forest Foundation, a nonprofit advocacy organization. Together, these trees suck up about 10 percent of U.S. carbon …