A Federal appeals court has issued a ruling that could block logging on thousands of acres in the U.S. Pacific Northwest, saying new studies must be undertaken to assess the impact of the timber harvest on local fish populations. The 9th Circuit Court of Appeals, in a decision handed down late Thursday, upheld a lower court ruling halting some 23 federal timber sales in Oregon's Umpqua River Basin because the National Marine Fisheries Service had failed adequately to consider the impact on endangered salmon runs.