It might have been that we sprang full blown from the forehead of Zeus or that some outside-of-the-galaxy empire attempted to colonize Earth in pre-glacial time when there were spruce forests in Iowa. Actually, of course, we got here because the founders of the State Agricultural College and Model Farm required that forestry be taught and Section 1621 of the Code of Iowa for the Ninth General Assembly formalized that requirement back in 1880. That still doesn't answer the "How come?".