Reviewed October 1993

G5150, Increase Woodland Products Through Timber Stand Improvement

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Increase Woodland Products Through Timber Stand Improvement

John P. Slusher and H.E. Garrett
School of Natural Resources
Clell Solomon
Missouri Department of Conservation
Ivan L. Sander
United States Forest Service

What is timber stand improvement? Timber Stand Improvement (TSI) denotes management practices that improve the vigor, productivity and quality of stands of trees.

In Missouri, young tree stands have become established readily following cutting or fire. But tree quality, species composition and individual tree form are often undesirable. Further reduction in quality comes when the better trees are harvested, leaving the bad ones, and when fire-scarred trees remain. The average Missouri woodland contains about 20 percent cull trees and produces at less than one-third its potential.

Using timber stand improvement

Many options are open to woodland owners. They may use a TSI program to increase the woodland's value for timber products, water, recreation, forage, wildlife, natural beauty, or for special products. Fortunately, work done to improve one use also benefits others in most cases.

Various practices used and tree species selected should fit the chosen emphasis for the woodland. The number of trees to keep depends on species, type of site, management goals and size of the trees. Professional foresters are available to help determine a woodland's potentials and limitations and to help develop and carry out a suitable management plan.

Types of trees usually removed are:

  • Cull trees and wide spreading "wolf" trees.
  • Trees inferior because of their species.
  • Trees interfering with the growth and development of selected desirable trees.
  • Damaged trees (broken off, bent over, fire scarred, seriously barked, etc., but expected to live at least one cutting cycle).
  • Seriously diseased trees or trees serving as a breeding ground for undesirable insects.

It is important to remove or kill these types of trees as soon as possible after an area has been logged to properly release younger trees. Variety is important in a woodland environment, so those trees necessary for den trees, aesthetics or special foods should be selected and retained in the stand when beginning a program of TSI.

The following practices are among those used in Timber Stand Improvement.

Site preparation for natural reproduction in understocked stands means preparing the site to allow natural seeding or resprouting of desirable species, or underplanting seedling stock to fully use the available growing space. This practice is used in poorly stocked stands to fill large openings and increase stand density, or to improve the species composition.

Thinning is cutting trees from an immature stand to increase rate of growth and improve the form of the remaining trees. Proper space varies depending on species, purpose of management and quality of the location (site). Table 1 gives a range of spacing for trees of various diameters.

Table 1
Tree spacing

Tree diameter Spacing range Tree diameter Spacing range
2 inches 4.6 to 6.5 feet 9 inches 14.3 to 18.7 feet
3 inches 6.1 to 8.2 feet 10 inches 15.6 to 20.4 feet
4 inches 7.6 to 9.9 feet 11 inches 17.0 to 22.1 feet
5 inches 9.0 to 11.6 feet 12 inches 18.1 to 23.8 feet
6 inches 10.3 to 13.4 feet 13 inches 19.4 to 25.6 feet
7 inches 11.6 to 15.0 feet 14 inches 20.8 to 27.2 feet
8 inches 13.0 to 17.0 feet 15 inches 21.9 to 29.0 feet
Certain species or management purposes may require other spacings. In any thinning, the tallest desirable trees are usually favored.
Source: "Even-Aged Silviculture for Upland Central Hardwoods," USDA Agriculture Handbook 355.

Release is removing or killing undesirable older overtopping trees to encourage fast growth and better quality of vigorous young desirable trees.

Pruning is removing limbs to produce the maximum clear lumber or veneer in the butt log. Prune only selected hardwood trees where high-value species are grown on good sites. This is recommended primarily in managing black walnut.

In pruning lower limbs of young trees, don't remove too much of the food-producing leaf surface of the tree. At least one-half of the living crown of the tree should be left intact. In general, trees should be pruned before they reach 8 inches in diameter. Limbs to be removed should be pruned before they reach 2 inches in diameter to reduce the wound size, to ensure proper closing and to lessen the impact of entry by insects or disease organisms.

Vine removal
On some areas vines do considerable damage to trees. Vines not retained because of wildlife food value, fall color, etc., should be killed at the same time other stand improvement work is done. Remove them by cutting them as low to the ground as possible and immediately treating the stump with a herbicide.

Special problem of sprout selection in TSI

Many Missouri hardwood species sprout heavily after fire or cutting. Sprouts grow rapidly and often form multiple-stemmed clumps. Use these guidelines for deciding how to handle sprout clumps.

  • Seedling sprouts, originating from severed seedlings, are as good as seedlings if the clumps are thinned to reduce crown competition and to avoid bad stump conditions from developing at the base when the trees become older.
  • Tree stump sprouts are less desirable than seedling sprouts, but they may develop into good-quality stems, depending on the size of the stump and the origin point of the sprout. Many hardwood sprouts decay through the large wound left at the base of a sprout when the parent stump rots away.

Sprout stands are best managed before they reach 20 years of age. Early treatment permits better selection of trees from the standpoint of attachment to and size of the parent stump, and greatly lessens the danger of decay from wounds left in cutting companion sprouts.

The best trees to leave come from seedlings, seedling sprouts or sprout clumps arising from stumps 4 inches or less in diameter. Sprouts from larger stumps may be selected if they arise very low on the stump and if the parent stump wound is small.

If early treatment is made in a young stand, it will enter maturity with the crop trees primarily single stemmed. Where there has been no early treatment, pole stands of sprout origin are likely to consist of sprout groups. After companion sprouts, joined at the base with a V-shaped crotch, have grown several inches in diameter, it is usually difficult to remove one without leaving a large wound at the base of the other, through which decay will develop. Twins of this type should be left alone. Where the sprouts have a low U-shaped crotch between them, or are entirely separated from each other above ground, one or more can be removed.

TSI cost sharing and technical assistance

Cost sharing practices are available for TSI. For further information, contact your local MU Extension center, Missouri Department of Conservation District Forester, or County Agricultural Stabilization Conservation Service Office.

Free technical assistance on all timber management practices is available through local District Foresters of the Missouri Department of Conservation.

Methods of removing trees from competition

The landowner should keep in mind that in many cases a properly conducted timber sale (improvement harvest) can accomplish a great amount of TSI. Undesirable trees that are not merchantable may be removed by cutting, dozing, brushhogging, girdling, or by chemical control. Chemically treating large trees is more economical than felling and is more certain to kill them than is girdling. Where control of resprouting is desired, chemicals are most effective.

Silvicides and herbicides are chemicals that act as translocation poisons, plant hormones or growth regulators, contact poisons, or soil sterilants. Some of the more common herbicides used in TSI operations are 2,4-D amine, triclopyr, AMS, picloram, glyphosate, dicamba, MSMA, or cacodylic acid.

All of these chemicals can injure sensitive trees, crops or ornamental plants if they are not used properly according to label instructions
Many are volatile and their vapors and spray drift will damage desirable plants, especially on windy days.

Silvicides and herbicides can be applied as follows:

  • Frilling or mechanical injection. Cuts are made through the bark and into the growing tissue completely around the tree. A suitable chemical, such as 2,4-D amine, is then applied to the fresh cuts. Mechanical injectors can be purchased or rented that apply the chemical at the time they make the cut. Hard-to-kill species, such as ash and hickory, should have a complete, continuous cut well into the sapwood. Many species may be killed with cuts spaced at intervals several inches apart.
  • Stump treatment of trees that have been cut. The stump should be thoroughly wetted with a chemical carrier mixture immediately following cutting.
  • Basal spraying may be used effectively on trees less than 4 inches in diameter. Spray chemical-oil mixture on the lower 12 inches of the trunk, wetting the bark thoroughly.

G5150 Increase Woodland Products Through Timber Stand Improvement | University of Missouri Extension