Timber stand improvement is the removal or deadening of undesirable trees, shrubs, and vines in a forest stand. It is a major forest management tool to help woodland owners achieve their management objectives. Once ownership objectives are identified, the less desirable trees can be removed to favor the growth of those that better satisfy the owner’s objectives (e.g., quality timber, wildlife habitat, etc.). At the same time, woody plants that pose a threat to human health or safety, such as poison ivy, can be eliminated. Several timber stand improvement techniques can also be used to create standing dead trees to provide wildlife habitat such as perches, dens, and foraging trees for animals and birds.
Timber stand improvement can be accomplished by cutting the less desirable woody vegetation or by killing it in place. Undesirable trees with commercial value can be sold, making the timber stand improvement operation an income-generating forest management activity. Some undesirable trees may be used for lumber, firewood, or other products. Grapevines might be used for wreaths. In most timber stand improvement operations, however, the undesirable vegetation is of little economic value or use. Although it can be cut and left in the woods, the safest and most efficient way to remove undesirable vegetation is often to kill the trees, shrubs, or vines and leave them standing.
The most effective method for killing standing trees, shrubs, and vines usually involves the use of an herbicide. For those who prefer not to use herbicides, cutting, frilling, girdling, or mechanical removal can be used. However, physical methods of deadening standing trees that do not use herbicides are generally less dependable (particularly with hard-to-kill species such as red maple, hickories, and dogwoods see Table 1), and take longer to be effective than methods that incorporate herbicides into the treatment.
Selected Timber Stand Improvement (TSI) Techniques
Five practices are commonly used as timber stand improvement (TSI) techniques:
- frilling or girdling
- spaced cuts or injection (hack and squirt)
- basal bark spraying
- cut stump application
- foliar spraying
It is essential that you read the entire label of an herbicide before application. The label contains complete instructions for use, along with other valuable information such as personal and environmental safety considerations and procedures. Many labels also list information about the effectiveness of the herbicide’s ability to control different species of trees, shrubs, and vines. All herbicides are not equally effective in controlling different species.
Herbicides, like all pesticides, are approved (labeled) for specific uses by the Environmental Protection Agency (EPA). These approved uses are listed and described on the herbicide’s label. Because labeling may change at any time, you should verify that a particular herbicide is still labeled for your intended use. For example, before applying an herbicide to a cut stump, ensure it is a practice listed on the label.
Frilling or Girdling
Girdling and frilling are methods of killing standing trees that may be done with or without an herbicide.
Girdling involves cutting a groove or notch into the trunk of a tree to interrupt the flow of sap between the roots and crown of the tree (Figure 1). The groove must completely encircle the trunk and should penetrate into the wood to a depth of at least 1/2 inch on small trees, and 1–1 1/2 inches on larger trees. Girdling can be done with an ax, hatchet, or chain saw. When done with an ax or hatchet, the girdle is made by striking from above and below along a line around the trunk so that a notch of wood and bark is removed. The width of the notch varies with the size of the tree. Effective girdles may be as narrow as 1 or 2 inches on small-diameter trees, and as wide as 6 or 8 inches on very large-diameter trees. When a chainsaw is used to girdle, two horizontal cuts between 2–4 inches apart are made completely around the tree when no herbicide is used (Figure 2) and one horizontal cut is made completely around the tree when herbicide is used (Figure 3).
Frilling is a variation of girdling in which a series of downward-angled cuts are made completely around the tree, leaving the partially severed bark and wood anchored at the bottom (Figure 4). Frilling is done with an ax or hatchet.
By themselves, girdling and frilling are physical methods to deaden trees that require very little equipment and may be done without herbicides. Both techniques require considerable time to carry out, particularly with an ax or hatchet. Girdling with a chain saw is much faster. The effectiveness of girdling and frilling depends on the tree species (see Table 1), and on the size and completeness of the girdle or frill. To be effective, girdles and frills must completely encircle the tree. Because frills can heal-over more easily, girdling is usually more effective.
The effectiveness of girdling and frilling can be increased by using herbicides. With frilling and girdling, water-soluble herbicides are most commonly used to get maximum movement of herbicide within the plant. When using water-soluble herbicides, the herbicide/water mixture is commonly applied by squirting it on the girdle or frill until the cut surface is wet. Hand-held, pint or quart spray bottles, such as those available at local garden stores, are ideal for applying herbicide to the girdle (Figure 3). Again, note that a single, rather than double, chain saw girdle is used when a water-soluble herbicide is to be applied (Figure 3).
Exceptions to using a water-soluble herbicide for girdling and frilling are forestry herbicides that contain the ester formulation of 2,4-D + 2,4-DP, such as Patron 170 and Super Brush Killer. They are labeled for use with frilling in an oil carrier, and the recommendation is to fill the frill with the mixture. They are commonly applied with a backpack or hand-held, hand-pumped sprayer.
Spaced Cuts - Tree Injection
Tree injection (sometimes referred to as hack and squirt) involves introducing an herbicide into the undesirable tree through spaced cuts made around the trunk of the tree with an ax, hatchet, or tree injector (Figure 5). The procedure can be visualized as a discontinuous frill with a small amount of herbicide placed in each cut. Make non-overlapping, horizontal cuts completely around the tree with an ax or hatchet into the sapwood (the outer area of lighter-colored wood in the stem cross section). Cuts are approximately 2 inches long and are spaced with their edges 1–3 inches apart, depending on the tree species and the herbicide being used. A small amount of herbicide is then placed in each cut using a pint or quart spray bottle (such as those available at garden stores). The amount of herbicide to be placed in the cut is specified on the herbicide label but is generally 1–2 milliliters. There are a variety of tree injectors available including the “hypo-hatchet,” which is a hatchet with an herbicide reservoir that injects herbicide when the blade cuts into the tree.
Tree injection is generally more effective than mechanical girdling or frilling without herbicide because of the use of herbicide. However, on difficult-to-control species, such as red maple, hickories, and dogwoods, a continuous frill or girdle with herbicide may be necessary to obtain acceptable control. For this reason, many commercial TSI (timber stand improvement) contractors routinely use a single chain saw girdle with herbicide on all species to maximize effectiveness.
As with most of the herbicides suggested for use with girdling and frilling, the herbicides for tree injection are mostly water-soluble materials that move vertically and horizontally within the tree to create a chemical girdle.
Basal Bark Spray
Basal or basal bark spraying is a technique to kill small trees, shrubs, and occasionally vines by spraying an herbicide on the lower 12–18 inches of the trunk (Figure 6). The intent is for the herbicide to penetrate the bark and kill the tree and any basal buds that might sprout. Herbicides used for basal spraying are generally applied in oil carriers. This technique is effective on trees less than 4–6 inches in diameter. As bark becomes rougher and thicker, the technique becomes less effective. Care must be taken when the herbicide is applied to minimize the amount that runs into the soil. This is important not only from an environmental-quality standpoint, but also to avoid damaging nontarget trees. Because the roots of trees often extend well out beyond their crowns, the roots of an adjacent, desirable tree could extend below the trunk of a tree being basal sprayed. If excess amounts of herbicide were applied to the treated tree, the adjacent desirable tree could absorb the herbicide and be killed or seriously damaged.
Cut Stump
When a tree or vine is cut, there is a high probability that the stump will sprout. When this is undesirable, the sprouting can be eliminated by treating the cut stump with an herbicide. Herbicides can be applied to the stump in many ways, the most common being to spray with a backpack or hand-held sprayer.
How much of the stump needs to be treated depends on the formulation of the herbicide used. Many of the herbicides labeled for cut stump application are water soluble. With these materials it is not necessary to treat the entire stump. The critical area of the stump that must be treated to prevent sprouting is the sapwood and bark of the stump’s cut surface (Figure 7). Stump treatment with water-soluble herbicides must be done immediately after cutting the tree or vine in order to be effective. If treatment is delayed, adequate downward movement of the herbicide will not occur, and sprouting will not be eliminated.
Some herbicides labeled for cut stump application are formulated to be mixed with oil. These materials do not move readily within the plant but they do penetrate the bark. To be effective in suppressing stump sprouting, the entire stump, particularly the bark and exposed roots, must be thoroughly sprayed (Figure 8). Timing is less critical with these materials because they are not as dependent on movement downward from the cut surface to distribute the herbicide. In situations where immediate treatment of stumps is not possible, an herbicide in an oil carrier should be used rather than one in a water carrier.
Treatment with an oil-carried herbicide is also recommended in the spring when treating species that exhibit a spring “sap flow,” such as maples (Acer), grape (Vitis) and ironwood (Ostrya). Water-carried herbicides will usually not be adequately absorbed to be effective during the spring sap flow.
Foliar Sprays
With woodland owners having to deal with non-native invasive plants, foliar applications of herbicides may now be a part of a landowner’s management plan. Many of today’s non-native invasive plants have a waxy coating on their leaves requiring an herbicide application that includes a surfactant to ensure that the herbicide adheres to the leaves. Equipment for these applications can be hand-held and backpack sprayers, along with sprayers mounted on ATV and UTV vehicles. Using a wick to apply herbicide to the leaves may also be a viable option.
Timing for foliar applications can be critical. Early spring applications are typically not as effective as applications later in the summer and into fall. At this point plants are pulling in resources to get ready for winter dormancy. Applying herbicides to plants later in the summer and into the fall increases the likelihood that the plants will die (Figure 9). Some plants such as winter creeper and bush honeysuckle are still actively growing late into the fall.
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Additional Resources
For more information on sprayers and other information on controlling trees, shrubs, and vines in your woodland, check out the following resources:
- Proper Calibration and Operation of Hand Can and Backpack Sprayers (FABE-531)
- How Much Chemical Product Do I Need to Add to My Sprayer Tank? (FABE-530)
- Relative Effectiveness of Herbicides Commonly Used to Control Woody Vegetation in Forest Stands (F-0051)
- woodlandstewards.osu.edu
Originally written in 1997 by Randall B. Heiligmann, Associate Professor of Forestry, The Ohio State University.