Complex sentence: Weyerhaeuser is one of the largest pulp and paper companies in the world; the world's largest private owner of softwood timberland; and the second largest owner in the United States, behind International Paper.
Split into simpler sentences: Weyerhaeuser is one of the largest pulp and paper companies in the world. It is the world's largest private owner of softwood timberland; and the second largest owner of United States timberland, behind International Paper.