However, new uses for the residual by-products of lumber and pulp manufacture are being discovered all the time. Many natural chemicals may be extracted from wood chips during the pulping process to produce products such as turpentine, plastics, food flavorings, and photographic film. Apart from mulch and fuel, some tree barks are processed to obtain tannins, dyes, adhesives, and even medicines. Although leaves and needles are usually left on the forest floor to replenish the soil and prevent erosion, in some cases products such as special oils may be extracted from them. Over the road, by rail, and by barge.
Delivery radiuses for rail and barge hauls can be somewhat greater, because of economies of scale.
Increasing numbers of mills receive wood after it has been chipped from facilities closer to where it was harvested. Chip mills provide competitive wood markets to landowners in new areas. Every year, we harvest a little bit more. In 1920, U.S. pulp mills consumed about 12 million tons of wood. In 1997, over 250 million tons were used.