Alaska's Tongass forest sparks battle over logging WASHINGTON (Reuters) - Environmental advocates readied for battle in Congress this week over what they maintain is an erosion of protections for the biggest, oldest trees in Alaska's Tongass National Forest, often called the crown jewel of the U.S. forest system. A vast swath of woodland that stretches along the southeast Alaskan coast and inland over more that 17 million acres (70,000 square km), the Tongass is one of the last temperate rainforests on Earth with centuries-old trees critical to wildlife habitat and Alaska's salmon fishery. Legislation expected to be considered on the House of Representatives floor this week would cede nearly 6 5,000 acres (263 square km) of public land in the Tongass to the native-owned Sealaska Corporation. Conservation groups say Sealaska would clear-cut some of the last remaining old-growth trees - cut down all trees in a given area - and take ownership of prime recreational sites along bays and at the mouths of salmons streams. Environmental advocates also say Sealaska would engage in the selective logging practice known as high-grading - disproportionately taking the biggest, oldest trees. This practice, the advocates say, not only destroys wildlife habitat and contributes to soil erosion but releases climate-warming carbon into the atmosphere during processing. "This is the biggest and oldest old-growth, the crème de la crème of ancient forests," Jane Danowitz of the Pew Environment Group said in a telephone interview. This legislation would allow these last remaining ancient forests to be commercially logged and even clear-cut by a single corporation. Sealaska disputes this and other claims by environmental groups and says the bill, which is supported by Alaska's congressional delegation, actually would allow the corporation to move away from old-growth logging. That would support a U.S. plan to make the transition from old-growth logging to logging of second-growth trees in national forests, Sealaska's executive vice president, Rick Harris, said. It would also fit with Sealaska's mission to redress long-standing wrongs against native people in the area. All of its approximately 21,000 shareholders are ethnically at least one-quarter Alaska native, Harris said from Juneau. Stuart Pimm, a professor of conservation at Duke University, said the environmental damage resulting from the legislation could last for centuries. "These are some of the biggest trees on the planet," Pimm said by telephone. If logged, "You're taking out an enormous amount of carbon. It's probably going to end up as carbon dioxide in the atmosphere ... You're doing something that's going to cause irreversible damage for hundreds of years. Forests are among the world's largest reservoirs of stored carbon. When trees are burned or processed, they release carbon into the atmosphere, which contributes to climate change. Pimm was among 300 scientists who signed an open letter to be released Monday asking members of Congress to vote against the bill. However, Sealaska's Harris said the measure would allow the corporation to give back parts of the Tongass that have only old-growth forest, and take instead lands already in use for timber with up to 50 percent second-growth trees. It also would get title back from the U.S. government for some properties with cultural value to Alaska natives, "because the federal government has not done a good job of management," Harris said. The measure that would let Sealaska pick different sites in the Tongass forest is part of a wide-ranging package of legislation involving U.S. wilderness areas called the National Security and Federal Lands Protection Act. Among its other provisions, the bill would give operational control of federal public lands within 100 miles of the Mexican and Canadian borders to the U.S. border patrol, which conservationists say could open national parks, wildlife refuges and other public lands to development and road-building. The legislation also would expand grazing privileges for private operations on federal rangelands and reduce environmental scrutiny of grazing practices, the Wilderness Society said in a statement. Reporting By Deborah Zabarenko, Environment Correspondent; Editing by Bill Trott