The forests of the Southern United States were little influenced by man until the mid-19th century when they become the focus of an early export lumber business. Longleaf pine (Pinus palustris Mill.) was the choice species due to its straightness and self pruning that produced high quality lumber and high resin content that limited decay and insect attack. The South's original longleaf pine dominated forest is estimated at 90 million acres. As the supply of virgin stands began to decline in the Carolinas around 1860, harvesting gradually moved south and west and by the early 1900s was concentrated in the West Gulf Region. The introduction of railroad logging increased the efficiency to the point that insufficient long leaf trees remained uncut to provide for regeneration.