How do you turn hundreds of thousands of acres of smallish trees into a profitable product? If you’re the Campbell Group, contractors for the Four Forests Restoration Initiative, you do it the old-fashioned way: Convert timber into lumber. Company officials say they will forgo more costly biofuel efforts for now as they prepare to thin 300,000 acres of northern Arizona forests. But the company faces a challenge even larger than the small trees. The logging industry has all but vanished from this region of the country. To thin that many acres, they’ll need drastically more loggers, trucks and mills. At...