Weyerhaeuser CEO Devin Stockfish said home-improvement projects are a key driver of lumber prices.  Lumber prices have fallen from May's record highs, but experts say they will stay elevated for several years.  A truck-driver shortage is also threatening to push prices even higher.  The CEO of Weyerhaeuser, one of the world's largest private owners of timberland, said the housing boom is not the only reason lumber prices are soaring — a surge in home-improvement projects is also driving the market.  While lumber prices have fallen back from May ...