Integrated Forest Vegetation Management

Competing and Invasive Forest Vegetation

One of the primary challenges to the health of our forests today is the shifting of plant species composition. This is due to a number of factors that favor the growth of certain species, referred to as 'competing' and 'invasive'. While native plant species all play a role in the ecosystem and are generally desirable, some natives are more desirable than others in certain situations, especially in timber management. Also, whether the forest is being managed for timber or not, a healthy forest will have a balance of numerous native plant species in each layer (under-, mid-, and overstory). Many forests today easily become dominated by a few native species that become overabundant. These prevailing native species are commonly called 'competing' plants.

Today's forests are also greatly threatened by ever-expanding populations of non-native or exotic plant species. Unlike native plants, exotic plants have very few, if any, positive contributions to the ecosystem and any positive qualities they do have are heavily outweighed by the negative effects that they cause. Exotic plants that grow and spread in natural areas and affect the native ecosystem are called 'invasive' plants. The official federal definition of an invasive species is one that is "non-native to the ecosystem and causes or is likely to cause economic or environmental harm, or harm to human health." Therefore, we do not use the term 'invasive' to refer to aggressive or overabundant native plants, because invasive plants, by definition, are exotic.

In forest ecosystem management, the term 'interfering' can be used to encompass both competing and invasive species.

A better understanding of the impacts created by competing and invasive vegetation in forests is needed. Competing and invasive forest vegetation impacts regeneration success, proper timber stand development, and native plant and wildlife species diversity (biodiversity). Interfering plants limit future forest species diversity and thus future timber value. They do this primarily by casting dense shade on the forest floor as well as competing for water, nutrients, and space that would otherwise be available for more desirable species.

Many factors contribute to the development of competing and invasive forest vegetation. These factors include shady understory conditions, preferential browsing by white-tailed deer, poorly planned and executed timber harvesting practices, and increasing invasive plant species abundance. Many species of competing and invasive plants are shade-tolerant and thrive in shady understory conditions beneath forest canopies. Deer, by selectively browsing preferred species, shift forest understories to less preferred plant species. This includes natives like hayscented fern, striped maple, beech, ironwood, mountain laurel, blueberry, huckleberry, and spicebush and many exotic plants. Poorly planned and executed timber harvests, known as high grading, leave behind trees with low commercial value. This practice has resulted in a shift towards less desirable and poorer quality tree species in our forests. Lastly, the increasing abundance of invasive plants is directly influencing the ability of forests to retain native plant and wildlife diversity.

Most woodland owners recognize the presence of at least a few undesirable plant species considered competing or invasive. In some cases, these plants become overly abundant to the point they interfere with ownership objectives. Interference might include: the development of competing plants in the understory (e.g., beech or fern) that impede desirable hardwood regeneration; invasive plants crowding out native plants and impacting wildlife habitats; and poor quality, undesirable tree species being left following a timber harvest limiting future potential. In these situations, undesirable plants may warrant control to achieve ownership objectives.

Each situation of undesirable plant control is unique. Integrated Vegetation Management (IVM) is a set of principles that helps guide the range of strategies used to address competing and invasive plant problems. Similar to Integrated Pest Management (IPM), IVM combines a number of approaches as a way of managing vegetation: cultural (silvicultural), manual/mechanical, biological, and chemical. Consider IVM a subset of IPM.

Five-Phased Approach to Integrated Forest Vegetation Management

1. Scout, properly identify, and map locations of undesirable plants, defined as those considered competing or invasive.
2. Learn life cycles of undesirable plants, including reproductive strategy and mechanisms used to spread.
    - What contributes to the success of the plant and what makes it difficult to control?
3. Define threshold levels of abundance based upon management goals, priorities, and abilities.
    - Thresholds will differ depending on plant species and owner objectives. For example, does the owner wish to reduce a plant's abundance or completely eradicate it from the site?
4. Begin control, use as many IVM practices as practical in concert with each other.
5. Evaluate results and keep accurate records. Modify the control program as needed.

Successful vegetation management incorporates a set of practices into a well-planned program. Any given site will have a different history and combination of species to consider. Careful examination of each situation is necessary considering species, extent, size, time of year, and available treatment options. Routinely review results and modify plans as necessary to ensure desired level of control is met.

Fundamental Principles of an Integrated Forest Vegetation Management Program

• Whether to control a plant depends upon management objectives, species, abundance, location and forest age.
• Preserve desirable plants, they provide a valuable service by occupying space that might otherwise support competing or invasive plants.
  • Preserving desirable plants is equally as important as controlling problem plants.
• Keep invasive plants under control and from spreading into uninfested areas and adjoining properties.
• Recognize and treat competing and invasive plants prior to harvesting timber. This is important because:
  • Logging slash can impede access and raise control costs.
  • Increased light will cause competing and invasive plants to flourish.
  • Herbicide treatments may damage or kill desirable regeneration after the harvest.

Cultural (Silvicultural) Control

Cultural control practices tend to enhance the growth of desirable plants and make the environment less suitable for competing and invasive plants. Cultural controls strive to prevent a competing or invasive plant problem by maintaining a healthy mix of desirable plants. Cultural control practices alone may not be enough to prevent competing and invasive plants from establishing. Maintaining a vigorous and healthy forest helps reduce undesirable infestations.

Cultural Control Practices

The following is a list of cultural control practices used in forests to suppress and/or prevent competing and invasive plant establishment.

• Implement proper timber harvesting practices.
  • Use regeneration methods that create light conditions appropriate for chosen species.
  • Thin overstocked stands leaving healthy, desirable trees properly spaced.
  • Keep land disturbance from roads and landings to a minimum.
• Use specific preventative measures during planting projects.
  • Select and plant only native species adapted to site conditions.
  • Revegetate bare soil areas as soon as possible.
  • When seeding roads and landings use certified weed-free seeds.
  • If bringing in topsoil, nursery plant soil, and mulches, monitor for weeds originating from seeds and rootstock.
• Prevent over-browsing by maintaining white-tailed deer populations at levels appropriate for available habitat.
• Remove soil and vegetative material from logging equipment and other vehicles before entering site.
• Monitor property frequently and eradicate small infestations before they become major problems.
• Educate neighbors about the importance of identifying and controlling invasive plants.

Manual/Mechanical Control

This control approach involves hand or machine removal of competing and invasive plants. Manual control practices generally involve physically pulling plants or breaking stems while mechanical removal typically involves cutting target plants using tools or machinery.

Hand pulling is practical for small, isolated infestations and individual, shallow-rooted plants. Pulling works best on annuals and biennials where the entire root system is removed. Pulling is not practical for large infestations of perennial weeds, shrubs, and trees with extensive root systems. For easiest removal, pull plants when soil moisture is high. To prevent further spread, pull plants before seeds mature. Keep soil disturbance to a minimum so buried seed is not exposed and other plants do not invade the site.

Many weeding tools, including loppers and power equipment, can be used to cut competing and invasive plants. For larger infestations, specialized brush mowing equipment is available. Cutting competing and invasive plants removes their competitive height advantage. Cutting at the proper time of year can also prevent seed production. In most instances, cutting or mowing alone is ineffective as many plants respond by producing large numbers of vigorous sprouts. When done repeatedly and often, cutting can deplete stored root reserves of some perennial plants, eventually starving the plant, but this is usually impractical. For dense infestations of large interfering plants, mowing can provide access to the site and may be the only way to initiate control.

Mechanical Control Practices

The following is a list of manual/mechanical practices used in the forest for controlling competing and invasive plants.

• Hand pull or dig individual plants and small infestations when first discovered. For best removal, pull plants when soil moisture is high.
  • Small trees and shrubs may be pulled using a commercial-grade tool called a shrub wrench. These tools enhance human strength by using a lever action to pull roots from soil.
• Periodically cut woody competing and invasive plants using loppers, power saws, and/or weed whackers with blade attachments.
  
  • To reduce root reserves and remove the competitive advantage, make the first cutting to perennial plants in early summer immediately following full leaf-out.
  • Manual/mechanical methods, such as pulling or cutting, are not as efficient as herbicides at controlling competing vegetation and are ineffective and/or impractical for controlling many plants.
• Mow fields and meadows on a three-year cycle to prevent establishment of invasive plants.

Biological Control

Biological control involves one type of organism preying on another. In vegetation management, biological control is mainly used on exotic plants, rather than native plants. The most common approach is to search the exotic plant's native range and identify insects or diseases known to affect the specified exotic plant.

The key to successful biocontrol is finding an insect or disease that will thrive after introduction and control only the targeted plant species. Researching new biological control agents is a process that takes years to ensure there will be no unintended negative impacts before a control agent is released. The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) is responsible for regulating introductions of species brought into the United States for biocontrol.

After the initial biological control agent introduction, it may take years before their populations become large enough to control targeted plants. Additionally, most biocontrol agents have limited spreading ability within the introduced range, so intentional introductions are usually required for each isolated population of target plant species, and more than one introduction may be required to establish a population in a particular site.

Biological control measures reduce undesirable plant populations to manageable levels rather than eradicating them completely. They can provide long-term suppression to some invasive plant problems. However, due to the long, expensive, and labor-intensive process of developing biocontrol agents, most biological control research revolves around agronomic pests and weeds. For plants that are more problematic in forests and natural areas, biocontrols are currently available for only a couple of species; mile-a-minute and purple loosestrife.

Other Biological Control Practices

Prescribed grazing by domestic livestock, primarily sheep and goats, is also a form of biological control. Livestock grazing on palatable competing and invasive vegetation can control some species but, like other biocontrols, this form of control rarely results in eradication. Most livestock species are preferential grazers, meaning they select the most palatable species first. Also, most undesirable plants will re-grow or return from seed after the grazing has ceased.

Using goats to control undesirable plant species in woodlots has had some success. Several studies have examined how to manage herd-stocking levels, how to assess potential success, and how to sustain forest and herd health. It can be useful for reducing the size and abundance of invasive and competing plants, but grazing will need to be followed-up with herbicide treatments for complete control of the re-growth. Grazing is also best used in sites where undesirable vegetation dominates, as the livestock will most likely eat any desirable plants as well. While it can be useful in certain scenarios, prescribed grazing tends to be costly and herds of livestock do cause significant soil disturbance.

Chemical Control

This control method involves using herbicides, pesticides specifically designed to control plants. Today's forestry labeled herbicides are a low-risk, productive, and effective method for controlling competing and invasive plants. In forest management, herbicides reduce competition between undesirable vegetation and valuable crop trees. They also aid in establishing regeneration, enhancing wildlife habitat, and facilitating road maintenance. Herbicide applications are part of most IVM programs.

Herbicide treatments are used to reduce competition between undesirable vegetation, such as this hayscented fern, and planted or naturally established tree seedlings.

Herbicide Uses/Control Practices

Forestry herbicides are used to:

• Control undesirable vegetation including trees, shrubs, vines, and herbaceous plants
• Increase forest productivity
• Prepare sites for natural tree regeneration and planting
• Boost tree seedling survival and growth rates
• Remove non-crop trees
• Release naturally established and planted trees from weed competition

No single herbicide, rate, or application method works for all vegetation management needs. Each situation requires advanced assessment to ensure the safest, most efficient, and cost-effective chemical control program is applied. Extensive research and testing have provided low-risk, effective herbicide prescriptions for controlling most competing and invasive plant problems.

Plant species, distribution, density, size, and the time of year all affect herbicide recommendations. Additional factors such as soil type and weather conditions are important because they affect plant growth, herbicide uptake, and translocation.

When treating extensive areas, broadcast treatments using helicopters or vehicle-mounted ground equipment may be necessary. These treatments are generally non-selective applications. Selective herbicide application methods are available to target individual plants or small patches with little or no impact to desirable vegetation. With selective applications, the herbicide is applied directly to the targeted plant. These methods include directed foliar sprays, cut surface, and basal bark applications. For detailed herbicide application methods consult the Penn State Extension Herbicides and Forest Vegetation Management publication.

Skidder-mounted mistblowers provide a non-selective understory treatment necessary to control interfering vegetation when trying to naturally establish hardwood seedling regeneration.

Herbicide Treatment Guidelines

Many competing and invasive plants are perennials, with extensive root systems. Herbicide treatments often offer the best means of eradication because they can control root systems without exposing soil to erosion or re-invasion. For effective herbicide treatments follow these guidelines:

• Use herbicide that is most effective at controlling the target species.
• Apply herbicide at the optimum time of year and lowest rate that provides the desired level of control.
• Follow prescribed application methods on the label.
• Adhere to all label precautions.
• Be patient, results may not be evident until the following growing season.

Pennsylvania Forestry Herbicide Use Sheets

Below you will find tables on herbicide use and application methods. Penn State Extension provides this information as a service. They are intended as a guide and not meant to be all-inclusive. Each table lists active ingredient, trade name(s), application equipment, application method, mixture, and time of year. Information is directly from product labels and material safety data sheets.

Before using any pesticide, read and follow the label. Following requirements and recommendations on the manufacturer's label prevents many potential problems that may arise from incorrect use. Any use of a pesticide contrary to instructions on the printed label is not legal or recommended.

No discrimination is intended and no endorsement or support of an individual product or company is given or implied by Penn State Extension. Author assembled the most reliable information available at time of publication. Due to constantly changing labels, laws, and regulations, author can assume no liability for recommendations.

For specific situations check with company sales representative or herbicide distributors for application rates, time of year, equipment, and costs.

Table 1: Common Forestry Herbicides

Herbicides commonly used in forestry are available under a variety of trade names. Therefore, it is best to become familiar with active ingredients, also referred to as the "common" name. The following table lists alphabetically by common name (active ingredient) forest-labeled herbicides approved for use in Pennsylvania. The trade name and manufacturer are shown in the columns that follow. Trade names are grouped according to active ingredient. A summary sheet is provided on each product.

This information is taken from product labels and material safety data sheets. (See Crop Data Management Systems, Inc. for more information.)

Generally used to control individual trees greater than 1 inch in diameter. Stem injections use a hatchet or lance-type tree injector calibrated to deliver the proper amount of herbicide with each blow. Frill-girdle applications use a hatchet or similar device to make frills or cuts at a downward angle. A spray bottle is used to apply herbicide to the cuts. Cuts must penetrate the bark into the living tissue or sapwood. Label recommendations indicate proper spacing of frills and injection sites. Do not allow material to run out of the cuts. Not recommended for use during periods of heavy sap flow.

Used to control resprouting of hardwood stumps. Herbicides are applied to the freshly cut stump surface. For water-soluble herbicides, spray or paint the living tissue or sapwood immediately after cutting. If using an oil-based mixture, treatments can be applied to stumps up to 1 month following cutting. Spray the sides of the stump to the root collar and the sapwood around the entire stump surface until thoroughly wet.

Generally used to control thin-barked trees less than 6 inches in diameter at the ground line. Applications are made directly to the intact stem at the base of the tree or shrub. A low-pressure backpack sprayer is used to wet the lower 12 to 18 inches of the stem completely around tree, including the root collar area (and any exposed roots if treating a root-suckering species). Do not spray to the point of runoff.

Used as a treatment to control many annual and perennial weeds and woody plants. Application is made directly to the soil surface using an exact-delivery spot gun applicator. Spray is directed at the soil within 2 to 3 feet of target plant root collar, or in a grid pattern across entire treatment area. The square grid pattern can range from 3 to 6 feet between soil application spots.

Herbicide site preparation treatments for hardwood plantings enhance seedling survival and growth. Site preparation treatments applied in advance of planting reduce competition from unwanted vegetation and provide increased light, nutrients, and moisture to newly planted trees. The herbicide used will vary depending on site characteristics and species planted.

Herbicide site preparation treatments for natural hardwood regeneration improves germination, survival, and growth of desirable tree species. Competing vegetation is controlled in advance. As new seedlings become established they are free to grow. Site preparation treatments reduce competition from unwanted vegetation and provide increased light, nutrients, and moisture to newly germinating tree seedlings.

Herbicide release treatments free existing tree seedlings, planted or naturally-established, from competing vegetation. These are "selective" applications made to control competing plants without injuring desirable tree seedlings. Hardwood release treatments are applied with backpack sprayers or ground machinery. The application method, chemistry used, and time of year are important so as not to harm existing seedlings.

Herbicide site preparation treatments for conifer plantings enhance seedling survival and growth. Site preparation treatments applied in advance of planting reduce competition from unwanted vegetation and provide increased light, nutrients, and moisture to planted seedlings. The herbicide used will vary depending on site characteristics and species planted.

Conifer herbicide release treatments free existing trees, planted or naturally-established, from competing vegetation. They can be applied by hand, using backpack sprayers, or made with helicopters and ground machinery using selective herbicides. The chemistry used and the time of year is important so as not to harm existing seedlings. These "selective" applications control competing plants leaving desired conifers free to grow.

Evaluate Results

After implementing any vegetation management practice, inspect the area and evaluate the results. Maintain a record of the type(s) of practices implemented, species of vegetation treated, date, and weather conditions before, during, and after application. Know the objectives of the control program when evaluating the results. In some cases, suppression of treated vegetation is sufficient; in others, complete eradication is desired.

Evaluate vegetation treatments after about two months, at the end of the growing season, and then again for several years thereafter. When using herbicides, initial activity and possible injury to non-target desirable vegetation is usually apparent two to four weeks after application. The full effectiveness of brush and perennial weed control measures may not be apparent for at least 12 and sometimes up to 24 months following treatment.

Evaluation is an ongoing activity. It allows for adjustments in rates, products, and timing of treatments. Plan for any additional control measures that may be needed.