Logging would more than double, more cattle would be allowed to graze, and forests could be aggressively thinned under proposed revisions to a management plan for the Sierra Nevada unveiled yesterday by the U.S. Forest Service. The sweeping changes to the Clinton-era Sierra Nevada Framework would allow timber companies to cut trees up to 30 inches in diameter in old-growth forests, well over the usual limit of 12 inches. Environmentalists are unhappy about the proposed revisions, which, they say, would do little if anything to redress decades of environmental degradation in the area. Regional Forester Jack Blackwell is expected to approve the plan, but Sierra Nevada Protection Campaign Director Craig Thomas said he anticipated that a standoff between the Forest Service and enviros would result in a legal “train wreck.”