Better Timber From Farms

by BENSON H. PAUL

STRONGER timber grows in farm woods when the farmer applies the rules of good forestry. Accessibility to all portions of the woods allows scattered cutting throughout the area as needed. Removal of poor and diseased trees or thinning in crowded places favors the better trees and hastens their growth much as weeding a garden promotes the growth of better vegetables.

Among hardwoods like ash, hickory, and oak a rapid and continuous growth of the trees in diameter will develop wood of high strength and toughness. On the other hand, some uses require soft wood that works, carves, and shapes easily. Low shrinkage and freedom from warping are qualities that give a high preference to certain woods, among them yellow poplar, basswood, and black walnut.

The unit weight of wood, or its specific gravity when completely dry or at a known degree of dryness, may be used as a yardstick of certain qualities. Its specific gravity is the ratio of the weight of a given volume of oven-dry wood to the weight of an equal volume of water. A great many tests at the Forest Products Laboratory in Madison, Wis., show how specific gravity affects the quality of wood in different ways. Woods with high specific gravity are generally strong, hard, difficult to work, and have high shrinkage. Woods with low specific gravity are generally soft, weak, easily worked, and have low shrinkage. It follows that woods of uniform specific gravity will have a high degree of uniformity in these other qualities. There will also be less waste in manufacture, fewer rejections by the purchaser, more profit for the producer, and better satisfaction to the consumer.

Unformity in wood is a good watchword—uniformity of growth, of weight (whether heavy or light), and of shrinkage or swelling with changes in weather. Uniformity of growth, which the farmer can control, will promote uniformity in the other desired qualities and result in a more satisfactory product.

In investigations of hardwoods, including white ash, the true hickories, rock elm, sugar maple, yellow poplar, and several kinds of oak, we found that uniformly maintained or uniformly accelerated growth in diameter produced heavy and strong wood suitable for uses where great strength is desired. Such wood is used for axe handles made of ash and hickory; bearing blocks, bowling pins, and flooring made of sugar maple; and bending stock of rock elm and oak.

Studies made by the Forest Products Laboratory in farm woodlands show how growth conditions affect wood quality. A farmer in Ohio owned a woods in which there was a good stand of white ash trees approximately 60 years old. The farmer placed a high value on the trees for future income and was adverse to cutting any of them, even for experimental study. It was evident that in some places the stand was overcrowded and growth of the trees in diameter was retarded accordingly.

We made cross sections of trees in the stand and found a reduction of more than 25 percent in the specific gravity of the wood from the inner portion of the sections outward for some trees, and an average reduction of 18 percent for the entire stand. In another crowded stand of white ash the specific gravity averaged 11 percent lower for the last 15 to 30 years than for the first 30 years of the life of the trees.

To prove whether the reduction in specific gravity of the wood accompanying retardation of growth resulted from crowding, we studied other white ash trees in a stand where heavy cutting had taken place 30 years earlier. In that stand the ash trees of pole size had responded to the improved growth conditions that resulted from the cutting by producing more wood per tree than trees of the same age in the crowded stands. Also, the wood in cross section of the trees where cutting was practiced was uniformly high in specific gravity and of better quality for handle stock than most of the wood in the ash trees of the crowded wood lots.

Hickory responded to changes in growth conditions in the same way. It had the highest shock resistance when cut from trees with well sustained growth in diameter. Second-growth hickory has better strength than old-growth hickory because second-growth trees have had less competition and grow more rapidly. Old-growth hickory that grew more and more slowly in dense forests had a good deal of light, brash wood. In such old trees the sapwood, or white-hickory portion, was the weakest part of the whole tree. For a long time hickory buyers avoided certain areas of old-growth forests in their search for stock of high strength and toughness. More recently, as good hickory has become more difficult to find, many buyers have learned to select hickory on a basis of its growth rate, from either old growth or second growth, and thus have obtained considerable amounts of strong hickory from the. more rapidly grown trees of both.

Hickory trees can be sold when they are 8 or 10 inches in diameter for use in handles, or picker sticks for textile looms. Rapidly grown trees contain much sapwood (white hickory) which, although no stronger than heartwood (red hickory) of equal weight, is liked better by buyers because of its appearance.