WOODLAND Thinning by Preserving Better Trees Often Profitable

Wherever farming has invaded formerly timbered areas, remnants of second-growth forests usually occupy the soil least suitable for cultivation.  The value of these bits of woodland is often very high, but frequently their importance as shelter to crops and as sources of fuel, posts, poles, and other farm timbers is not fully realized. A little well-directed care in protection from fire, removal of insect-infested or diseased trees, prevention of injury to seedlings by overgrazing, and intelligent selection of trees in cutting to relieve crowding would mean more complete use of the soil and would improve the quality of the timber produced.  Beneficial thinnings can often be made at the time of ordinary utility cuttings by selecting the trees good enough for the purpose desired, rather than the best trees of the stand. The selection of the thriftier, more promising individuals for preservation is made easier by a simple classification universally used by foresters.

When crowding begins in a stand of trees of the same age, some individuals secure an advantage in the competition for soil nutrients and light and become taller than the others with larger crowns and trunks. These largest trees are called dominants. They are the more rapid growers, the most vigorous of which would survive to maturity if natural competition proceeded undisturbed. The trees somewhat shorter than the dominants but still reaching into the upper crown canopy are called codominants. Such trees are declining in vigor and would become overtopped and die if unrelieved by cutting.  Still lower in the scale of size and vigor are the intermediates, usually less than two-thirds the height of the dominants, with very small poorly developed crowns. Completely overtopped or understory trees are called suppressed. They have very small crowns and are on the verge of perishing. Still standing, or fallen to the ground, are the trees which have died from suppression.

In the natural struggle for existence the weaker dominants decline to codominants, these in turn become intermediates, the intermediates become suppressed, and the suppressed trees die. If the stand is undisturbed the understory trees never gain a place in the upper crown canopy. This unregulated competition often retards the growth of the entire stand.

The first thinning usually becomes necessary at an age of 30 to 40 years. First consideration should be given to removal of dead, diseased, broken, or poorly formed trees. When competition has not been too prolonged, thinning from above, or in the dominant stand, will greatly improve the vigor of the understory trees. If large material is needed and the dominants have attained suitable size, this method of cutting often coincides with practical necessity. Care should be taken in felling not to injure the smaller trees to be retained.  If smaller material can be used and larger timber is desired later, the thinning should be made from below, removing enough of the weaker suppressed and intermediate, and perhaps some codominant trees to improve spacing and relieve the dominants from competition.

As a precaution against destruction of the entire stand by uncontrolled fires, slash from the cutting should be made into fuel or piled and burned in such a way as not to injure the remaining trees. This may also prevent development in the slash of insects, which under certain conditions emerge from the limbs and tops and attack standing trees. Care should be taken not to permit the fire to spread through the stand and destroy the litter and leaf mold. The feeding roots of trees are usually very near the surface and removal of the litter permits drying of the soil to a sufficient depth to kill the rootlets and retard growth.