Authors: James T. Walters, former Extension Associate, Department of Forestry, College of Natural Resources, Virginia Tech and James E. Johnson, Associate Dean of Outreach, College of Natural Resources, Virginia Tech.
Publication Number: 420-144, posted March 2000
Chapter 3: Maintaining And Enhancing Tree Growth
Maintaining and enhancing tree growth, or productivity, is an important part of sustainable
forestry. Ideally, increasing productivity provides us with more forest products and reduces
the amount of forestland that must be devoted to timber production. For example, if you can
increase the productivity of your primary forest stands, then you can place less emphasis on
timber production in your streamside management zones and special areas. As we place more
demands on the forest, tree growth will become a key characteristic.
There are two ways to look at tree growth. In a biological sense, tree growth refers to increasing the size of trunks, branches, and roots. In an economic sense, growth refers to an increase in value. Tree value and usefulness as forest products, aesthetics, wildlife habitat, and other uses are related to tree size.
Productivity is influenced by many factors, but generally they can be divided into two broad groups: site characteristics and stand characteristics. Site characteristics are qualities of the land where the forest is located, and are usually related to either climate or soil. Stand characteristics are attributes of the timber in the forest. Examples of stand characteristics include tree size, health, and species.
Comparing the productivity of forests in western Virginia to that of forests in other regions is a difficult task. Our forests are more productive than those in some regions and less productive than others. However, for producing high-quality hardwood timber, our forests are more productive than forests in many regions. In fact, some of the best hardwood timber in the world comes from our Appalachian Mountains.
The most important limitation to productivity in many western Virginia forests is soil quality. The quality of a site in our region can often be estimated by investigating the rock found under the soil. In general, the sites that are located in limestone areas have high timber productivity. In contrast, the sites located in regions that contain shale are generally less productive. Forests on sandstone-based soils usually have intermediate timber productivity. The type of bedrock is important because limestone sites tend to have deeper, moister soils and more nutrients than sites with sandstone or shale.
There are several management strategies you can enact on your property to maintain and enhance timber
productivity. These strategies include maintaining and improving site productivity, maintaining and
improving the productivity of your current stand of timber, and establishing productive stands of new
timber.
Strategy #1: Maintain and Enhance the Productivity of the Site
Many attributes of a site make it productive for growing timber. The climate and topography of the area are certainly important inputs to productivity. Sites that receive high amounts of precipitation are generally more productive than dry sites. Temperature can influence the length of the growing season and can cause defects that slow tree growth. Aspect of the topography has a significant influence on the type of vegetation that will grow on a particular site. Location of the forest on the mountain is important in determining timber productivity. Forests on tops of ridges are generally less productive than forests in coves and stream bottoms. Needless to say, there is not much that we can do to change the climate or topography of our forests.
The quality of the soil is another important factor in determining the productivity of a site. Soils that are deep, moist, and rich in nutrients usually support productive forests. Furthermore, in a productive forest, the tree roots are able to grow through the soil. Unproductive sites sometimes have hard, dense, and rocky soils that discourage root growth. For example, most tree roots do not grow well in soils with high clay content. Protecting and enhancing site characteristics can make your forest more productive. In particular, you can prevent soil erosion, fertilize special sites in your forest, prevent compaction during timber harvests, allow logging slash to decompose, and prevent livestock grazing.
Soil erosion can greatly decrease the productivity of your forest. Most soil nutrients are in the 6 to 12 inches directly below the leaf layer. Nutrient levels diminish dramatically at greater depths. If the surface soil is taken from the site by erosion, then the site becomes much less productive. You may remember that erosion is a natural process that occurs in all forests. While this is true, natural erosion is generally offset by the creation of new soil, so it usually does not affect site productivity. Our goal as forest managers is to prevent our management activities from causing erosion beyond natural levels. A sustainably managed forest will not have higher-than-normal erosion rates. Minimizing erosion helps maintain site productivity in our forests.
Erosion prevention measures, such as seeding with grass, are important in maintaining site productivity |
Erosion control techniques were discussed in great detail in Chapter 2. We are particularly interested in preventing erosion from roads and timber harvests. Most erosion originates from these two practices. The primary strategies for erosion control on forest roads are to divert water from the road whenever possible and to slow runoff on the road. Our goal is to place runoff from the road into natural drainage systems. The key to preventing erosion from a timber harvest is the protection of sensitive areas such as skid trails and log landings. We generally protect these areas through careful harvest planning that outlines Best Management Practices for the forest.
Trees need a variety of nutrients to grow. They get most of these from the soil. However, the soil in our forests sometimes does not contain enough of a particular nutrient. In these cases, nutrient deficiencies can limit site productivity. The most common nutrient deficiencies occur when there is not enough nitrogen, phosphorus, or potassium.
Farmers have used fertilizers to increase the productivity of their crops for decades. Until recently, however, fertilization of forests was never considered a viable management option. Advancements in fertilizer technology and increasing timber prices have caused some forest landowners to think seriously about fertilizing the forest.
The use of fertilizer in forests should be carefully considered from the standpoint of sustainability. Sustainable forestry is about managing a renewable resource - the timber in our forests. Many of the fertilizers that can be applied to forests, however, are not renewable at the rates they are currently used. Therefore, the continuous fertilization of our forests over a long period of time is not a sustainable forestry practice.
There are special sites, however, that have been abused in the past and have lost some of their natural productivity. Fertilizing these sites just once or twice may help them to regain that lost productivity. For example, some sites in western Virginia that were farmed in the early 1900's have become much less productive. The agricultural practices on these sites depleted the supply of nutrients important for tree growth. It is very difficult for these sites to regain productivity without fertilization because natural development of nutrients is very slow. Fertilizing a site may increase the natural production of nutrients. In these cases, fertilization is a temporary measure we can use to restore a site to its natural productivity.
Forest fertilization is uncommon in western Virginia because it is very expensive. Increases in productivity do not usually offset fertilization costs. However, you may want to consider this as a management alternative if your forest contains special sites that would be improved by fertilization. Your forester or county Extension agent can give you more information about fertilization.
Soil compaction occurs when the soil is squeezed together. When soil is compacted, the amount of air in the soil is decreased and the soil can become very hard. These soil conditions are not conducive to growing trees and other forest vegetation. Trees need softer soil so that their roots can grow. Softer soil contains more water and oxygen, which are important for good root growth. Soil compaction simply decreases the productivity of a forest site.
Soil is compacted whenever we step on it, but that compaction is insignificant. When a heavy machine drives across the soil, however, compaction can be much more severe. Therefore, compaction is a big concern whenever our forest management activities involve large machines.
Certain soils are susceptible to compaction. In particular, soils that are moist or high in clay content are more easily compacted than dry and sandy soils. If the soil in your forest is sensitive, there are several steps you can take to prevent compaction. First, you can limit the use of heavy equipment on the site. If you want to harvest timber from a forest with sensitive soil, you should ask your forester about logging alternatives that do not use conventional machinery. If your site is fairly stable, you might be able to find a logger who uses lighter equipment with wide tires. This equipment compacts the site much less than ordinary logging equipment, but is more expensive to operate and is not well suited to extremely steep sites with large timber.
Restricting the operation of heavy equipment in your forest during the wet season also prevents compaction. Dry soil is much more stable than wet soil. Summer and fall are relatively dry seasons in western Virginia, and the soil in your forest is usually much more stable during these months. If heavy equipment operates only during the summer and fall, then compaction of your forest soil will probably be minimal.
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Logging slash is the wood debris left after a timber harvest and includes branches, chunks, bark, and stumps. Traditionally, logging slash has been left in the forest because there has been no market for these wood materials. Over the years following a timber harvest, slash decomposes, providing valuable nutrients for the soil, increasing organic matter in the soil, and improving soil structure. It also provides nesting and escape cover for wildlife. Decomposing slash is an important source of nutrients in a sustainable forest. Technological advancements in paper and wood product manufacturing, however, have increased the markets for smaller logs. The amount of slash that is left on the site has been decreasing steadily as these advancements have occurred.
The best way to ensure that logging slash is left in your forest after a timber harvest is to include a stipulation in your timber sale contract that addresses slash disposal. Most loggers in western Virginia leave the tops and branches of trees in the woods, but you may want to make sure that the logger does not pile all the logging slash near the landing. Your forester will be able to help you write the timber sale contract and work with the timber purchaser in order to leave logging slash in your forest.
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On A Side Note ...
Visually Acceptable Harvesting Alternatives Increasing interest in the aesthetic value of the forest has stimulated the development of timber management techniques that have less disturbance on the appearance of the forest. One of the most promising of these techniques is the selective harvest of timber combined with timber stand improvement (TSI) practices. This technique is a visually acceptable manner of harvesting timber that can provide income from the forest. Selective harvesting, combined with TSI, can be relatively easy to implement in your forest, but should be used judiciously. If this technique is improperly administered, it can result in a high-graded forest containing trees of little or no value. The first step in implementing this technique is to specify tree species and characteristics that will lead to a tree's being harvested. A forester can inspect your forest and help you to make these decisions. The forester should mark trees that are undesirable due to species or other characteristics such as size or poor form. These trees will be removed in the TSI cutting. For example, you might specify that only trees that are small, crooked, limby, or unhealthy should be cut. The resulting forest should contain healthy trees that will provide a wide range of values, including aesthetic enjoyment, wildlife habitat, and good timber growth. An important step in administering a selective harvest with TSI is the creation and enforcement of a good contract. The contract should specify which trees are to be harvested and should place penalties on damage to residual trees. Furthermore, the contract should require the buyer to cut down marked trees, regardless of merchantability. Small trees that you want to be removed should be marked with paint at eye level and on the stump. When harvesting is completed, the only stumps that should be found are those with large diameters or painted bark. It is a good idea to require a performance bond from the purchaser so that you can repair any damages that occur during logging. A properly implemented selective harvest with TSI can provide you with income from your forest while maintaining an acceptable appearance. A harvest of this type will generate a small income, but leave a much more valuable forest behind for future growth and development. |
Livestock grazing has been common in forests located on farms, but causes problems in these forests. Livestock often travel the same paths when they move from one location to another, causing soil compaction. They also increase the potential for erosion by exposing bare soil. Livestock damage the fine feeder roots on your trees, making it more difficult for the trees to get water and nutrients from the soil. Finally, livestock frequently damage large roots and bark along the bases of trees, opening them to harmful insects, disease, and decay.
Livestock graze on young trees in your forest. These young trees are very important because they will take the place of old trees that die or are harvested. Heavy grazing makes it difficult to establish a new stand of timber when the older trees are removed. Heavily grazed forests often look like parks because there is little vegetation in the understory. The result of grazing is a forest that is unhealthy and has reduced timber value. This type of forest is not sustainable.
The best way to prevent grazing in your forest is to build a fence that keeps livestock in the pasture. This fence does not have to be elaborate. Many landowners simply use barbed wire or high-tension fence to keep livestock out of their forests. Fencing your forest is a management activity that you can probably perform yourself and will be a valuable asset for your forest.
Strategy #2: Maintain and Improve the Productivity of your Current Stand of Timber
Many factors influence the productivity of your current stand of timber. For example, there is only a limited amount of nutrients and water available on the site. Trees must compete with each other and with other vegetation for these resources. Competition decreases the productivity of your timber.
The mixture of tree species in your stand also has an important impact on timber productivity, because some species grow faster than others. For example, yellow poplar grows very well in many of western Virginia's forests. Black locust grows more slowly and does not get as big as yellow poplar. Although black locust is an important component of our forests, yellow poplar is much more desirable in terms of timber production. Insects and disease can have a tremendous impact on the productivity of timber in your forest. The gypsy moth, which eats the leaves of oaks and other trees, is a good example. Without leaves, these trees are much less productive. They also become less healthy and can even die if they are heavily defoliated or infected by a disease.
There are two primary ways we can improve the productivity of timber in our forests. First, we can improve the biological productivity of the timber and thus increase growth. Management activities that increase biological productivity include reducing competition and preventing insect and disease damage. Secondly, we can increase the economic productivity of the timber to make it more valuable. Management activities that increase economic productivity include removing unproductive trees from your forest and pruning trees. By increasing the productivity of our timber, we will increase the amount of timber that can be sustainably harvested from the forest. This will decrease the need to harvest timber in fragile and unique areas, which need to be managed according to their special needs.
A young stand of timber is one where the majority of trees are saplings -- trees less than four inches in diameter. A young stand of timber might be found in forests where timber has been harvested, older trees have died, or a field has grown into a forest. The trees in a young stand of timber are generally less than 15 years old.
There are several types of competition in a young timber stand. In very young stands, the trees must compete with grass, bushes, and other herbaceous species for nutrients, water, and sunlight. When the trees get older and grow taller, they are usually able to get plenty of sunlight. However, they still compete with herbaceous plants for water and nutrients. When the trees finally begin to branch out, they compete primarily with each other for sunlight. Their branches are fairly close to the branches of other trees, forming a compact canopy.
Natural resource managers often use the term "stocking" to refer to the number of trees found in the forest. Forests that are understocked have too few trees, while overstocked forests have too many trees. Forests that are well-stocked have an appropriate number of trees. Controlling competition is only important in overstocked forests because the trees are competing with each other for resources. In these forests, some trees would die naturally because there are insufficient resources to support all the trees. Understocked and well-stocked forests have less competition for resources, so competition control is not necessary. Your forester can tell you if your forest is overstocked.
The most common method of reducing competition in a young stand of timber is to control the growth of competing vegetation. We generally accomplish this by using herbicides or by cutting the competing trees. There are several techniques associated with each of these vegetation control strategies.
Herbicides are chemicals that are designed to control undesirable plants. Herbicides used in forestry are chemical compounds that disrupt plant metabolism, leading to death. Herbicides can be used to control competition in any young stand, and there are a variety of herbicides that can be used. Each is designed to control a particular type of vegetation. For example, some herbicides are designed to control grasses and others are designed to control small woody bushes. The best herbicide for controlling competition in your stand depends on the type of vegetation you need to control. If you want to control herbaceous vegetation in a very young stand, then the herbicide should be designed to control herbaceous growth. If you want to control trees that are competing for sunlight, then the herbicide should be designed for trees.
Herbicides must be used judiciously in sustainably managed forests in order to protect their natural character and features. The primary role of herbicides in sustainable forest management is in the restoration of improperly managed forests and abandoned agricultural fields. Herbicides might also be used to thin an overstocked stand. This would eventually occur naturally; we are simply accelerating it to reduce stress on residual trees. A herbicide treatment in these special cases is used to accelerate natural development.
Cutting down competing plants in your young forest is an option, but it can be very time-consuming. Young forests usually have many trees growing close together. However, you may be able to mow the herbaceous growth between young trees in a planted field. You could also use an axe, small chain saw, brush saw, or machete to control small trees in forests where sprouts are concentrated around old stumps.
There are relatively few young forests in western Virginia that receive competition control. Herbicides and manual control are often too expensive for individual landowners. However, a group of landowners might be able to provide sufficient demand to support a forest improvement crew. Furthermore, there are special instances in which your management plan might recommend competition control as a viable option. Examples would be old fields that have been planted with trees.
The two forest management practices for reducing competition in an older forest are thinning and prescribed burning. Thinning is the removal of trees from a forest to give the remaining trees room to grow. A thinning increases the growth of your forest and improves the health of remaining trees. Prescribed burning is the use of fire to control competition within the understory of a forest.
When you conduct a thinning, a logger will harvest a certain number of the trees in your forest. You may be able to sell these trees as pulpwood or sawtimber. The trees that are left after a thinning are called residual trees. They should be tall, healthy, and straight. Your forester will recommend how many trees to remove from your forest and mark those to be removed. Thinnings are usually conducted in forests that are overstocked. This information should be included in your forest management plan.
In the most common type of thinning, known as select thinning, the forester or landowner specifies exactly which trees to remove by marking them with paint or a ribbon. The logger then harvests the selected trees. Select thinnings usually produce very good results, but they are expensive to implement because every tree must be marked.
A special type of thinning that is gaining popularity is the crop tree release, a select thinning where special "crop" trees are encouraged. Crop trees are those that you plan to harvest when they are mature. They should be of a desirable species, straight, and free of defects. A crop tree thinning will focus water, nutrients, and sunlight on these trees. After the thinning, the crop trees should receive full sunlight and have room to grow on at least three sides. Trees that are not competing with the crop trees do not have to be thinned. Instead, they can be left to mature until the next harvest. They will improve the species diversity of your forest and may provide wildlife habitat or other non-timber benefits.
There are several factors you may want to consider when choosing a logger to conduct a thinning on your property. The logger should be able to thin the stand without damaging residual trees. A residual tree could be damaged by the logger felling a tree into its top and breaking out branches. Dragging a log against the trunk of a residual tree and scraping off bark would also result in damage. A logger could damage the site by compacting the soil with heavy equipment. Thinnings are best conducted by loggers with small equipment.
Forest thinning of poletimber and small sawtimber has not traditionally been popular in western Virginia because thinned trees had little market value, the increase in stand productivity was considered marginal, and labor-intensive logging systems resulted in high logging costs. Thinning is also impractical on steep slopes because there is too much damage to residual trees. However, thinning is becoming more popular as markets for pulpwood and strandwood increase, the value of sawtimber increases, and harvesting technology improves. Therefore, thinning may be a recommended practice in your forest management plan.
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Prescribed burning can be used in an older stand of timber to reduce competition within the understory.
These fires are usually low- intensity blazes that are hot enough to kill understory trees and shrubs, but
do not damage the bigger trees. Prescribed burning is also valuable because it encourages growth of
herbaceous species important for wildlife, favors the growth of oak seedlings, and gives your forest a
park-like appearance. Prescribed burning temporarily increases phosphorus, potassium, calcium, and other
nutrients. Furthermore, periodic prescribed burning greatly reduces the chance of a severe wildfire in
your forest by removing dead wood that could serve as fuel. Prescribed burning certainly has great
advantages if you can manage it properly.
There are several concerns associated with prescribed burning. If a fire is not properly managed, it can get too hot and get into the crowns of big trees. Fire is particularly difficult to manage on steep slopes. If a fire gets too hot, the mature trees are likely to die and, more importantly, the fire becomes much harder to control. In these cases, liability is a very important issue. You are responsible for the neighbors' forests and for any buildings and homes that might be located adjacent to your property. Hot fires also remove the litter layer of leaves and expose bare soil, which is easily eroded on steep slopes. It is certainly wise to carefully consider any plan for prescribed burning and to work with a burning contractor who has the equipment and experience to control the fire.
Prescribed burning has not been common in western Virginia because all the benefits have not been fully considered. Burning is becoming more common, however, in areas where wildlife management is an important objective, where landowners want to establish an understory of oaks for regeneration, where wildfire is a concern, and where insects and disease are major problems. If you are interested in these objectives, you may want to talk with your forester about the possibility of conducting a prescribed burn in your forest.
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On A Side Note ...
Clearcutting vs. Deforestation: The Clear Distinction It is very important to recognize the difference between clearcutting and deforestation. Clearcutting is a regeneration system in which timber is harvested so that shade-intolerant seedlings and sprouts can receive enough sunlight to survive. In contrast, deforestation is the removal of trees without regenerating a new forest. Deforestation occurs when land is converted to another land use such as agriculture, mining, or residential development. The differences between clearcutting and deforestation are substantial. Clearcutting can be conducted without damage to water quality, but a deforested site is likely to erode without some type of vegetative cover. Deforestation results in fragmented forests with smaller and less manageable tracts. However, a clearcut will regenerate with young trees within several years of harvest. Deforestation removes wildlife habitat, but clearcutting creates a productive early-successional habitat. A deforested stand carves a hole in a forested landscape, but a clearcut will quickly become part of a mosaic of different-aged forests. Finally, deforestation reduces the forest base that we have to provide future resources, but a clearcut establishes a new forest that will provide benefits for a future generation. Recognizing the difference between clearcutting and deforestation is an important step in understanding good forest management. |
Timber stand improvement (TSI) is a forest management practice that improves the timber quality of your forest by removing less desirable trees, vines, and shrubs. TSI is used in sustainable forestry to restore forests to a more natural state, in which valuable species such as oaks are prevalent. The vegetation removed in a timber stand improvement is usually not actually taken from the forest because it has little commercial value. Instead, it is killed and left to decompose. The remaining trees have less competition and there may be room for new trees to grow. Timber stand improvement is an important forest management activity if your ownership objectives include harvesting timber, but your forest has been poorly managed in the past.
There are several differences between forest thinning and timber stand improvement. Trees harvested in a thinning may be sold to a logger, but the trees removed in TSI usually have no commercial value. Thus, TSI usually results in a cost for the landowner. Furthermore, the focus of a forest thinning is different from that of timber stand improvement. Thinnings are used to improve the growth rate and species composition of the timber. Timber stand improvement will increase the growth of remaining trees, but it is used primarily to increase the value of the timber. Finally, the trees removed in a forest thinning are usually large, but trees and shrubs of all sizes might be removed in a timber stand improvement.
Timber stand improvement is useful in forests that have been "high-graded." "High-grading" is a term used to describe timber harvests in which only the best timber is removed. Low-value trees and trees with poor form are not removed during a high-grading harvest. These trees become the only source of seed in the new forest, and the trees in the new forest will likely be undesirable. High-grading is a very poor forest management practice. It is similar to a dairy farmer's selling the cows that produce the most milk, but keeping the ones that are not productive. This farmer would soon have a herd that does not produce very much milk.
Unfortunately, some of the forests in western Virginia have been severely high-graded. The landowners might have needed money at some point in time, and decided to harvest the timber. They probably did not seek assistance from the county forester or a consulting forester. These landowners might have received more money for their timber in the short term, but their forest was not very productive after the high-grading harvest. Aside from cutting every tree and starting a new forest, the best thing that can be done on high-graded forests is to perform a timber stand improvement.
The most common methods of killing undesirable vegetation are to apply a herbicide, cut it down, or girdle it. All three of these methods can be expensive to implement. Your forester can tell you more about the most common TSI activities in your local area.
Herbicides used in timber stand improvement are similar to those used in forest thinning. They contain chemical compounds that ultimately kill the tree. Application methods include spraying the bark of the tree or cutting the bark and spraying the exposed wood. The application technique will depend on the type of herbicide you plan to use.
Trees are rarely cut down in a timber stand improvement because there are more efficient ways to kill them. Cutting is most commonly used on vines and shrubs. A forest worker uses an axe, saw, or machete to cut the vine or shrub at the base. The best time to cut a vine is several years before a timber harvest. Sprouting of vines will be minimal if there is a heavy overstory.
Girdling is a technique where a knife or axe is used to cut a ring of bark from around a tree. The tree will then die because it cannot transfer water and nutrients from the roots to the leaves. Girdling is not very common today because modern herbicides are more effective and less expensive.
There are several opportunities to perform a timber stand improvement in your forest. You could do the work yourself, but this is hard work and is very time-consuming. The best opportunity to perform TSI work yourself is when you cut firewood from your forest. You can harvest trees that have little value as timber, but are good firewood. Your forester can recommend which types of trees are the best to cut from your forest.
You could also contact the county forester to see if there are any TSI contractors operating in your area. There may be a herbicide contractor or firewood cutter that you could hire to perform the TSI work. It is a good idea to ask the forester whether the contractor can choose which trees to remove, or if you should have those trees marked. You certainly do not want the contractor to remove good trees from your forest.
Another opportunity for TSI work on your property is when you have timber harvested. If you choose to harvest only a portion of your trees, you could specify in your contract that the logger has to either cut down or run over the undesirable trees in your forest. This contract stipulation would probably decrease the price of the timber, but would probably be cheaper than performing TSI work at another time. If you do not have this contract stipulation, you can still encourage regeneration of desirable trees by cutting or girdling the undesirable trees left following a harvest.
It is important to carefully consider all values of undesirable trees, however. Some trees may have little commercial timber value, but may be very valuable for wildlife food and cover. For example, a large, old, partly rotten beech tree may have many cavities for nesting and dens, and also may produce beech nuts for wildlife food.
Timber stand improvement has a specific place in sustainable forest management - as a restoration tool. Well-managed forests will not need improvement activities because they contain desirable trees of good form. TSI work in these forests to remove a few undesirable trees would not be economically feasible. Furthermore, commercially undesirable trees often have value aside from being useful for wood products.
Pruning is the removal of branches from the trunk of a tree. Forest trees are pruned to promote clear, knot-free wood. Knots can reduce the value of lumber cut from the tree, particularly in the first log, where the most valuable lumber is located. Pruning is most important in limby species such as white pine.
Trees often prune themselves. When the leaves on a branch do not receive much sunlight, the branch will eventually die. When the branch dies, the tree may heal around the base and the branch will fall off. This process is called natural pruning. Many of the tree species found in western Virginia are good natural pruners.
Some trees are poor natural pruners. When a branch on the tree dies, it does not fall off for a long time. Instead, the tree continues to grow around the dead limb. When the tree is harvested and lumber is cut from the log, the branch or knot will fall out, creating a hole in the lumber. Trees that are poor natural pruners include white pine and scarlet oak.
Proper pruning of a tree's lower branches can improve the timber quality. |
Pruning is not very common in western Virginia, because most of our trees are good natural pruners and pruning can be very expensive. You can encourage natural pruning by creating heavy competition when trees are young. White pines that compete with other trees for sunlight will grow taller so they can get as much light as possible. These trees will have fewer lower limbs than those that do not have to compete for sunlight. A stand that is being managed to encourage natural pruning is overstocked during the period when the trees are growing tall enough to have a limb-free butt log. When trees are older, the stand can be thinned to encourage timber growth.
You can also prune limbs from trees in your forest by cutting them off, but this activity takes a great deal of work and time. Cutting limbs from the tree is sometimes called artificial pruning. The market for timber must be very good in order for artificial pruning to be profitable. Pruning efforts should be concentrated on potential crop trees, valuable species, and trees with low forks. You can discuss pruning with your forester to get more information about artificial pruning in your locality.
Insects and disease are natural components of a forest. They provide a natural method of replacing old trees with healthy new ones. However, you probably do not want to lose the value of the old trees. Therefore, you may want to manage your forest to prevent damage by insects and disease. If you do have problems with insects or disease, there are several alternatives for managing the damage.
The first step in preventing damage by insects and disease is to monitor for infestations, thus giving yourself time to manage any outbreaks. Your management alternatives become limited if you do not find problems as soon as they occur.
Insects and disease have a much more severe impact on an unhealthy forest than on a healthy one. For example, gypsy moths may eat all the leaves from the trees in your forest. A healthy forest will probably just grow more leaves the next year. If your forest is unhealthy, however, the trees may not be able to grow new leaves and could become very weak. These weak trees would then be very susceptible to diseases and attacks by other insects.
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The keys to maintaining a healthy forest are to encourage a variety of tree species and to reduce competition
among your trees. There are trees that should be able to grow naturally in your forest and remain fairly
healthy. However, there are also trees that will not grow well on given sites. For example, red oak
grows well on moist sites, but would be unhealthy on a dry site. When you perform a thinning in your
forest, it is a good idea to leave trees that are well suited to the site. Furthermore, thinning
increases the health of trees by reducing competition for resources such as water, nutrients, and sunlight.
There are several options for managing insect and disease outbreaks after they have occurred. There may be a pesticide treatment for the insect or disease that has infested your forest, but many are very expensive. These pesticides are usually developed for application to yard trees. The best option in many cases is to perform a salvage harvest on the affected trees. By removing these trees, you may remove some of the insects or disease and can increase the health of the other trees in your forest. You may also be able to sell the harvested trees.
In some cases, there may not be a way to combat insect and disease infestation. The insect or disease may be very strong, or your forest may have been unhealthy. In these cases, the only option you have is to accept the losses of mature trees and encourage the development of a new forest that will be healthier and more resistant to insects and disease.
Strategy #3: Establish Productive Stands of New Timber
There are many complex factors that shape a forest, but every forest goes through several distinct natural life cycles. Forests begin as a young stand of seedlings and saplings established in an abandoned field, a harvested forest, or an area with heavy insect, fire, or windthrow damage. The trees grow and begin to compete for light, water, and nutrients. This young stand will probably contain more than a thousand trees per acre, but some of the young trees will die. There just aren't enough resources to sustain all of the trees. However, the surviving trees will continue to grow until they are mature. The mature stand may contain only 40 trees per acre.
When trees in mature stands die, they are usually replaced by trees that didn't need much light to grow. These trees were the only ones that could survive in the shady understory. Trees that don't require much light are called shade-tolerant. When all the trees from the original stand have died, the forest will be primarily composed of shade-tolerant trees. The most common shade-tolerant species in western Virginia are beech, hemlock, and sugar maple. These trees can continue to thrive in a mature forest.
The forest will remain in a mature stage with shade-tolerant trees until some type of natural disturbance occurs. This disturbance could be a large forest fire, an outbreak of insects or disease, or a very severe windstorm. After the disturbance, the forest will start over again as a new stand of seedlings and saplings. It is important to note that this could occur before the forest has had a chance to develop into a stand of shade-tolerant trees. This has traditionally been the case in many of the forests in western Virginia.
There are many opportunities for humans to intervene in the natural life cycle of the forest. These human impacts are sometimes accidental. For example, a careless camper may start a wildfire in an immature forest. This fire could cause the forest to start over as a stand of seedlings and saplings. However, we sometimes intervene in the natural life cycle of the forest for a particular reason. We might harvest timber in the forest or perform a timber stand improvement to encourage valuable timber species. We often influence natural forest cycles to produce forest products. Many of the products we desire come from trees that are not shade-tolerant. We sometimes intervene in natural cycles to promote and encourage the growth of commercially valuable species. Oaks and pines are examples of species that are not shade-tolerant.
When we conduct forest management activities, we are not necessarily changing the natural life cycle of the forest. We simply encourage the forest to move to a new stage in the cycle. For example, when we harvest timber, we encourage the forest to start over again as seedlings and saplings. When we thin trees from the forest, we encourage the remaining trees to mature. In sustainable forest management, we are managing the forest to provide products while maintaining its natural character and value. Our management activities should not significantly change the forest from a natural state.
One of the most important opportunities we have to influence the life cycle of the forest exists when the forest is starting as seedlings and saplings. Our management activities influence what types of trees will grow in the new forest and can make it healthier and more productive. Management activities you can perform in your forest include preparing the forest to grow new trees, encouraging the establishment of desirable trees, and protecting the new forest from damage by wildlife.
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On A Side Note ...
Shade Tolerance: Important Information for Forest Managers Shade tolerance refers to the relative ability of a tree to grow under shade. Tolerance is an important factor in making forest management decisions. For example, if you are interested in growing seedlings that require direct sunlight, you will need to choose management practices that allow sunlight to reach the forest floor. Conversely, if the trees you desire do not require direct sunlight, you can choose management activities accordingly. Tree species are commonly classified into three categories of shade tolerance: tolerant, intermediate, and intolerant. Trees that are shade-tolerant are readily able to reproduce and thrive under a thick canopy. In contrast, shade-intolerant species require direct sunlight to reproduce and grow. Intermediately tolerant species, as the classification suggests, require an intermediate level of sunlight. Trees that are commonly found in western Virginia forests are classified by shade tolerance in the following table.
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Site preparation is a term foresters use to describe the management activities that prepare the forest to grow new trees. These activities provide an environment that helps a desired tree species to grow. For example, consider that you want to grow oak timber in your recently harvested forest, but the understory is made up of red maple saplings. Because oak trees cannot survive in the shade, you need to get sunlight to the forest floor so the oak seedlings will have a chance to grow. You could cut down the understory so the oak seedlings can get enough sunlight to compete. This management practice would be considered site preparation.
There are three primary types of site preparation treatments: mechanical treatments, chemical treatments, and prescribed burning. Mechanical treatments involve the use of heavy equipment to clean logging slash, knock down large trees that were not harvested, and even cultivate the soil. Mechanical treatments can sometimes damage the forest by causing compaction and erosion. Chemical treatments involve using herbicides to control vegetation so new trees will have more sunlight and less competition. Prescribed burning is generally used to control understory vegetation before planting and to kill large trees that were not removed during harvesting. The treatments used to prepare a site will depend on the types of trees that will be in the new forest, the qualities of the site, the amount of vegetation, and the amount of slash that was left after a timber harvest. It is vital to consider the impact of your site preparation activities on the future forest. The minimal application of these techniques will help to ensure that the natural character of the forest is maintained.
Landowners who decide to establish hardwood forests have one very important site preparation alternative. They can cut down or apply herbicides to understory trees to allow sunlight to reach seedlings on the forest floor. This management activity is very important in stands where the understory is composed of undesirable trees, but where the landowner wants to have a forest with trees that are not shade-tolerant. These stands have usually been harvested, but not all the trees in the forest were removed. Therefore, site preparation is necessary to allow seedlings of desirable trees to survive. If you have recently harvested timber, it is a very good idea to talk with your county forester or a consulting forester about what types of trees will be in your new forest. The forester can recommend site preparation activities that will allow you to create a sustainable forest that meets your needs.
Intensive site preparation is more common in pine plantations than in hardwood forests. Pine trees are not shade-tolerant and they are usually planted, so they have more specific site requirements than hardwood trees. Site preparation is not very common in western Virginia because there are relatively few pine plantations. Intensive site preparation techniques that change the character and features of the natural forest are non-sustainable practices.
Forest regeneration is the process of reproducing a forest after a timber harvest or natural catastrophe. Regeneration will occur naturally as the forest changes stages in the natural life cycle. However, this is a good time for us to use forest management activities to influence which tree species will grow in the new forest.
The two types of forest regeneration are natural regeneration and artificial regeneration. Natural regeneration occurs when new trees grow from the seeds, sprouts, and root suckers of trees in the stand. This type of regeneration is very common in the forests of western Virginia. Artificial regeneration occurs when humans bring seedlings or seeds into the forest with the intent to establish a new forest with those trees. Examples of artificial regeneration would be planting pine or walnut trees.
Artificial regeneration is used to establish tree species that would not become established in the forest naturally. There are several reasons why we might want to establish these species. It might be a valuable timber species such as oak, walnut, or cherry. It might produce food for desirable wildlife species. Trees that are artificially regenerated might grow naturally in a later life cycle of the forest, but you might want to grow them immediately. Perhaps you are interested in establishing these trees while site characteristics are optimal for growth. Species that are sometimes artificially regenerated in western Virginia include white pine, red oak, and black walnut.
Two techniques for artificially regenerating a forest are planting and seeding. Planting is certainly more common in western Virginia, because seeding requires the establishment of a good seedbed consisting of moist, exposed soil. Creating a seedbed is usually more expensive than planting, but in special cases direct seeding may be a feasible alternative. For example, if a wildfire in your forest burns leaves and exposes the soil, then conditions would be favorable for seeding some tree species. Your forester can give you more information about sources of seed, techniques for seeding, and site preparation activities that will help the seeds grow into trees.
There are several ways to plant trees in our forests. The most obvious method is using a shovel, hoe, or some other tool to plant the seedlings by hand. Seedlings can also be planted with a planting machine, which can plant trees very quickly, but requires relatively flat and open ground to operate. Steep slopes and logging slash usually prevent mechanical tree planting in western Virginia.
The traditional tree-planting season in western Virginia is February to early April. Trees are dormant during this period -- they have no leaves and are not growing. The soil should be moist and firm when the seedlings are planted. When possible, avoid planting trees when the ground is frozen, dry, or very wet. Planting under these conditions is more difficult and the seedlings will not grow very well. If soil conditions are severe, many of your seedlings could die.
When you decide to plant trees in your forest, you will need to determine if you can do the planting yourself or if you need to hire a tree planter. For many landowners, planting trees themselves is not an option because their forest is simply too large. An average person can plant approximately one acre of trees per day. If you were planting a 50-acre field with white pine seedlings, it would probably take you at least 50 days. Therefore, most landowners contract with tree planting crews. You can talk with foresters, other landowners, and the Virginia Department of Forestry to obtain a list of tree planters. The best planting contractors will have a good reputation and experience in planting the types of trees you desire.
There are several things to watch for in your newly planted forest. First, look for tree seedlings that die. Seedlings can die because they have been improperly planted, the weather has been severe, or wildlife has browsed on them. If a large number of your seedlings die, you might consider planting more in the bare spots. The second thing to watch for is competition from grasses, bushes, and other seedlings. If there is heavy competition, you will need to use herbicides or mow around the seedlings to help them survive. Without weed control, tree planting is generally a waste of time and money. Good site preparation is also important in preventing these problems with your new seedlings.
Planting is used prudently in a sustainable forest. It is primarily employed as a restoration tool in abandoned farmland. Perhaps the most important consideration in artificial regeneration of sustainable forests is that the species being planted or seeded are native. Exotic species must be avoided in sustainable forest management.
Natural regeneration is ideal when natural forest conditions are favorable to growing desirable trees. Natural regeneration is very common in hardwood forests. Many hardwood trees regenerate naturally from both seeds and sprouts. In the mountains, pine trees usually naturally regenerate only on poorer sites, where they can compete with hardwoods.
The transformation from a seed to a seedling is a very complex process. First, seed trees must produce a good crop of fruit or seeds. These seeds can come from trees that are left after the timber harvest or may have come from trees before they were harvested. After a seed falls on the forest floor, it must be distributed to a site where it can germinate. The seed could fall directly from the tree onto an ideal germination site, but wind, water, or wildlife can carry it to a better site. Only a small percentage of the seeds that a tree produces will actually germinate.
When a seed has germinated, it requires very specific site conditions to become established. The site must be moist and the seed must be able to grow roots into the soil. Furthermore, the temperature must be within a particular range. If these conditions are not just right, the germinated seed will not survive.
The established seedling will also require special conditions. The amount of sunlight available for the seedling is a very important factor at this stage. Seedlings that are not shade-tolerant will not survive if they do not receive direct sunlight. Many seedlings do not grow into trees simply because there are not enough resources such as sunlight, water, and nutrients for all to survive.
It is apparent that natural regeneration from seedlings is dependent on many factors. If these factors are not ideal, then seeds will not be successful in becoming seedlings. The seed crop for the year could have been poor because of dry weather conditions. A heavy deer and squirrel population might have eaten the majority of the seeds that were produced. Perhaps a fire killed all the seedlings on the site, or an insect rendered the seeds infertile. There are many things that can cause problems with natural regeneration from seeds.
Many of the tree species found in western Virginia will sprout if they are cut, burned, or otherwise damaged. These trees sprout when the sugar stored in the roots is transferred to buds located in the stump or roots. These buds then grow similarly to the buds that are located on the end of a tree branch. Often, several buds on the same stump will grow in a clump of sprouts. Sprouting is most prolific from smaller stumps. You may have noticed trees in your forest that grow in a clump from the same stump. These trees probably grew from that stump when an old tree died. Stump sprouts were the primary form of regeneration of many of today's forests. Tree species that commonly sprout include oak, yellow poplar, maple, beech, and black locust.
If you are considering natural regeneration in your forest, it is a good idea to perform a regeneration survey. A regeneration survey involves looking at trees and shrubs in your forest to determine what types of trees will grow in the new forest. In particular, you are looking at the trees that are located in the understory and the trees that might provide a source of seeds or sprouts. If you have a good number of desirable tree species in the understory and those trees receive enough light to survive, then your new forest will probably have a good number of these trees. Although they may be trampled during a logging job, these young trees will grow back vigorously. Furthermore, if you have a large number of sprouting species such as oak and poplar, then there is a good chance that these species could grow back into the new stand. Your forester can help you with a regeneration survey and make recommendations about which species to expect in the new forest.
The timing of a timber harvest can have a very significant impact on the success of natural regeneration in your forest. For example, if you harvest timber in the fall or winter, then you can expect to have a large amount of sprouting in your new forest. Trees have been storing sugars in their roots all summer and there is a large supply for the sprouts. On the other hand, if you harvest your forest in the spring or early summer, there will be much less sprouting. The trees have used the sugars stored in the roots to survive through the winter and the sprouts will not be very aggressive. In general, harvesting in the spring or summer favors seed regeneration and harvesting in the fall or winter favors sprouting.
The type of harvest can also have an important impact on the success of natural regeneration in your forest, particularly for tree species that are not shade-tolerant. If you harvest all the trees from your forest, then there will be plenty of sunlight for seedlings and sprouts. However, if you only harvest a few trees, then the only seeds and sprouts that will survive are those that are shade-tolerant. Light is probably the most important factor in deciding which tree species will grow in your new forest.
The type of timber harvest is so influential on regeneration that different harvesting methods are sometimes called regeneration systems. Different regeneration systems have been developed in the past to meet the increasing needs of forest landowners. However, regeneration systems can be divided into two categories: even-aged and uneven-aged. The distinction between these two categories of regeneration systems is the age structure of the forest.
Forests that are managed with even-aged regeneration systems contain trees of approximately the same age. The trees and shrubs in the understory may be younger, but the dominant trees in the overstory are the same age. Even-aged timber harvests are commonly used to regenerate shade-intolerant species because they allow sunlight to reach seedlings and sprouts when a timber harvest is completed. Examples of even-aged regeneration harvests include clearcutting, seed-tree harvesting, and shelterwood harvesting.
Uneven-aged forests contain trees of many different ages. For example, five trees from an uneven-aged forest might be 90, 65, 40, 30, and 11 years old. Uneven-aged harvesting methods include single-tree selection, group selection, and two-aged cutting. Uneven-aged management is becoming more popular as more emphasis is placed on non-timber values of the forest.
Clearcutting is a common harvesting technique for regenerating shade-intolerant species. Clearcutting involves cutting down all the timber in the stand and either cutting or deadening understory trees that could shade the new forest. Clearcutting is simply a way of harvesting your forest so that new seedlings and sprouts can receive enough sunlight to survive.
There are several guidelines to follow when clearcutting your forest. It is a good idea to limit the size of clearcuts. Smaller harvests reduce the aesthetic impact on the forest. Where possible, create irregular edges around your clearcut so that it blends in with the landscape. You can leave a few trees in the clearcut to provide shelter and food for wildlife. Finally, it is wise to consider aesthetics and soil disturbance before deciding to clearcut. Properly conducted clearcutting is certainly a sustainable forest management practice.
The seed-tree regeneration system is an even-aged system that is similar to a clearcut, but leaves a few mature trees as a source of seed. Seed trees may be harvested after the new forest is established or may simply be left in the forest indefinitely. There should be enough trees to provide sufficient seed to regenerate the forest, but there should not be so many that they shade the new seedlings. Regardless of how many trees you decide to leave, you should only pick trees that are strong enough to withstand heavy winds and that have large crowns capable of producing good crops of seeds. Promote good genetics by selecting well-formed, desirable, and dominant trees in the stand.
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Shelterwood regeneration involves a series of small timber harvests that prepare the forest for
regeneration, encourage new seedlings, and remove the mature stand. The first harvest in a shelterwood
system will remove some of the mature trees so that there is enough space and sunlight on the forest
floor for the new seedlings and sprouts to grow. There should also be enough sunlight for shelter tree
crowns to expand and produce heavier seed crops. During this harvest, some mature trees are left as
a source of seed and to create site conditions preferable for regeneration of a desired species.
When the new forest is established, the second shelterwood harvest removes the remaining mature trees.
The primary distinction between seed-tree harvests and shelterwood harvests is that more trees are
left in a shelterwood system. Because there are always trees in the forest, some landowners think
seed-tree and shelterwood harvests look better than a clearcut.
It is a good idea to carefully consider which even-aged regeneration system to implement on your property. Seed-tree systems are uncommon in western Virginia because most of our desirable species can grow from sprouts and previously distributed seeds. Shelterwood harvests are becoming more popular because they protect the beauty of the forest during a timber harvest. The most common even-aged regeneration system, however, is still clearcutting.
Single-tree selection regeneration systems are uneven-aged systems in which light cuttings of mature trees occur every 10 to 25 years. Single-tree selection systems favor shade-tolerant tree species because large trees are always shading the forest floor. Therefore, there is not sufficient sunlight to regenerate seedlings that require a large quantity of sunlight.
Single-tree selection systems are not very common in western Virginia because we usually want to regenerate trees that are shade-intolerant. Furthermore, logging costs are increased and a good road system through your forest is necessary. However, single-tree selection can improve the aesthetics of timber harvests and can provide a steady source of income for the owner of the forest if shade-tolerant species are desired.
Some landowners confuse single-tree selection regeneration systems with "high-grading." Other names for high-grading include "diameter-limit" cutting, "select" cutting, and "logger's choice" cutting. There is a very important distinction between single-tree selection and high-grading. Single-tree selection harvests are conducted with consideration of regeneration. Trees that are poorly formed and some trees of undesirable species are harvested to make room for better trees. Only trees that are of good form are left in the forest. In a high-grading harvest, however, only the best trees are harvested. Poor-quality trees are left in the forest, even if they are mature. "High-grading" is inconsistent with sustainable forest management.
The group selection regeneration system consists of periodically harvesting small patches of timber throughout your forest. These small patches are essentially small clearcuts that are usually smaller than five acres, but must be big enough to allow sunlight to reach seedlings and sprouts that are not shade-tolerant. If these pockets are large enough, shade-intolerant species can be regenerated with some success. Group selection is particularly successful in regenerating shade-intolerant trees in the centers of the openings. Edges are generally lost to shade-tolerant species.
Group selection systems are expensive to implement because logging costs are higher and you need good forest roads. However, properly executed group selection can increase long-term income by allowing trees to grow into higher-quality classes rather than cutting them prior to financial maturity. This is particularly important with high-value species on good-quality sites. Furthermore, group selection may be a viable regeneration system if aesthetics is a major concern and you are interested in regenerating shade-intolerant species. Finally, group selection is a good regeneration system when edge and habitat diversity are desired to meet wildlife management objectives.
Two-aged regeneration systems are a compromise between even-aged management and uneven-aged management. Two-aged harvests are similar to shelterwood or seed-tree harvests, but trees that are not harvested will be left in the stand until the new forest is mature. Two-aged regeneration systems are becoming common where aesthetics is an important management objective.
There are several concerns in two-aged forest management. You will need to remove enough trees from the forest to allow sunlight to reach new seedlings and sprouts. Furthermore, only good trees should be left in the stand. These trees should be healthy, able to live a long time, and well-formed. Two-aged regeneration systems can be a good way to regenerate your forest while maintaining its beauty.
There are many considerations when choosing a regeneration system for your forest. You must determine your ownership objectives, inventory the trees and understory in your forest, and estimate the productivity of the land. These items should be outlined in your forest management plan along with recommendations about which regeneration system is best suited for your forest. If you don¼t have a management plan, it is a good idea to contact a forester and inquire about one. When you have determined your ownership objectives, your forester will be able to look at your forest and make a recommendation about regeneration systems.
Wildlife can cause serious problems for landowners who want to regenerate a forest. The most common damage is caused by deer, which browse on seedlings and sprouts. Deer browse is sometimes so severe that the forest cannot regenerate according to plans. The deer population may be so high that the deer have browsed the entire understory in your mature forest. If you decide to harvest timber in this forest, it can be difficult to regenerate new trees. Deer can also hinder regeneration in planted forests. Deer prefer to eat planted seedlings because these seedlings are often more nutritious than natural seedlings.
Although wildlife damage to regeneration is not widespread in western Virginia, there are several techniques for managing wildlife damage in your forest if it is severe. The best way to manage deer damage is to control the population of deer in your forest. A normal deer population will not usually cause problems in a regenerating forest, but if the deer are overpopulated they will browse on every small tree they can reach. Hunting is a common technique for controlling deer populations. Harvesting female deer maintains control of the expected annual population growth of deer herds living in the absence of natural predators. If you do not hunt, then your game warden can recommend a hunt club or group of hunters that are responsible and ethical.
There are other management techniques for controlling wildlife damage where populations are not excessive. These techniques usually involve shielding seedlings from wildlife or making the seedlings less appealing. You can shield trees with a tree shelter made of plastic tubing that is placed around the tree. The seedling grows inside the shelter so that it is out of the reach of deer. Similar shelters can be constructed from wire. Tree shelters are expensive and are usually implemented only in special cases. There are also chemical compounds that can be sprayed onto your seedlings to give them an offensive odor or taste. However, chemical treatments are only marginally successful, because the deer will still browse on the nutritious seedlings.
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