FO-06517 1995

To Order

Logging for the 21st Century: Forest Ecology and Regeneration

Mathew Smidt and Charles R. Blinn

Logging and Forest Ecology

Biodiversity
Nutrient Cycling
Forest Health

Logging and Forest Regeneration

Advance Regeneration
Stump Sprouts
Root Sprouts or Suckers
Seed Regeneration

Logging Methods
Conclusions
Glossary
Suggested Reading

Introduction

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Forest management is changing. Good management once meant simply protecting soils and regenerating forests following timber harvest. Today, however, we know that the forests need more than fertile soil and young trees to be productive over the long term. We also know that for many people wildlife habitat, recreation, and aesthetics are at least as important as timber production. This means managing for more than just trees. It means managing to protect the many other benefits that forests provide, too.

As our view of forest management is changing, so too is our understanding of how to maintain a productive forest. Maintaining forest cover is certainly the most important aspect. However, other things are important, too. The species of trees, shrubs, and other plants that regenerate, the removal of nutrients by harvest, and soil disturbance all affect forest productivity. Loggers and foresters today must pay attention to these as well as to traditional silvicultural considerations when planning and carrying out a harvest.

This publication provides loggers, foresters, and nonindustrial private forest landowners with information about forest productivity and forest regeneration. Alternative logging methods are suggested to maintain forest productivity and to promote forest regeneration. A glossary is included at the end of the publication to define key terms.

Logging and Forest Ecology

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An important part of preserving the long-term productivity of a forest is preserving its ecology — the links among its many living and nonliving components. Responsible logging today considers effects on various aspects of the forest ecosystem, including biodiversity, nutrient cycling, and forest health.

Biodiversity

Biodiversity, simply stated, is the variety of living organisms. Many of us think of rare and endangered species when we think of biodiversity. However, it's important to protect distinct populations or unique combinations of more common plant and animal species, too. Changes in forest habitat can cause a loss in biodiversity. That loss in turn can harm the ability of the forest to remain healthy over the long term.

We affect biodiversity when we convert forests to cities or farmland. One way to minimize the loss of many rare plant and animal species is to keep more land in forests. Because carefully planned traditional forest management and harvesting provide economic incentives for maintaining forest land, they can help conserve forest biodiversity.

We also affect biodiversity when we fragment forests. This happens when a disturbance creates "islands" of forest that differ from their surroundings (Figure 1). For example, some plants may not return to small farm woodlots after disturbances such as logging or grazing because the plots are isolated from sources of seed. Another example is the effect of turn-of-the-century logging in Minnesota, which fragmented the extensive pine forest into areas separated from each other by large blocks of aspen forest. This altered the ability of plants to migrate and recolonize the area. Such fragmentation may reduce diversity within species by preventing different plant populations from interbreeding. It also can affect wildlife species that need more extensive areas of similar habitat.

Figure 1. Forest fragmentation: Pine areas were fragmented by harvest. When the remaining pine areas are harvested or disturbed, the seed sources necessary to revegetate a similar pine type may be too far away.

Species diversity often increases following timber harvest because of invasion by plants that thrive in disturbed areas. At the same time, uncommon plants and animals that use understory habitats such as shaded, moss-covered logs may disappear. However, if seed sources are present in a nearby forest, the plant species can return to the logged areas as the new understory develops, retaining diverse and productive habitats.

Forests harbor a large variety of habitats that are home to specific kinds of organisms. These microhabitats — downed logs, snags, mounds caused by previous tree-falls, and so forth — are important components of forest diversity.

You can help maintain biodiversity in several ways. One is to minimize soil disturbance while harvesting. Second, try to keep at least one edge of the harvested area adjacent to mature forest. Third, change harvest boundaries or retain mature forest corridors between parcels to avoid isolating small parcels of mature forest. If you use corridors, make them at least as wide as the height of the trees, and wider if necessary to maintain forest light conditions in the interior. Selection cutting or thinning can help preserve many of the qualities and microhabitats of mature forest while providing income from timber harvesting.

This means thinking about biodiversity when developing a forest management plan for the area. By helping to maintain biodiversity, you are helping to conserve the quality of the forest habitat and making it easier for the forest to recover from disturbance.

Nutrient Cycling

Trees need a variety of nutrients to survive. Those required in relatively small amounts are called micronutrients. Examples of micronutrients include iron, copper, and boron. Nutrients such as nitrogen, phosphorus, and potassium that are required in larger amounts are called macronutrients. The supply of nutrients often determines how well trees grow and produce wood, leaves, fruits, or seeds. It may affect the species of plants that are present, too.

Nutrients move among the many living and nonliving parts of the forest. The movement of nutrients into and out of the forest and among components is called the nutrient cycle. All nutrients cycle, but the nutrients in highest demand — phosphorus, potassium, and nitrogen, for example — cycle rapidly through many steps

Nitrogen available to trees and other plants comes from dead organic matter, from the atmosphere through precipitation, or from the activity of certain microorganisms (Figure 2). Nitrogen forms that plants can use are very mobile and can be leached away by the percolation of rainwater through the soil or returned to the atmosphere by other micro-organisms. Nitrogen accumulated by trees is either returned to other parts of the forest ecosystem when the tree dies or is removed from the system when the tree is logged.

Figure 2. The nitrogen cycle: Nitrogen is in high demand by many organisms and is sometimes in forms that are very mobile.

Trees store nutrients in their leaves, wood, bark, and roots. Fast-growing species such as aspen contain high concentrations of nutrients in their trunks and branches. Most conifers (pines, spruces, firs) retain substantial amounts of nutrients in their needles. Spruces and firs retain more needles on the tree and consequently more nutrients than pines. At any given time only a fraction of a forest's nutrients is available for plant use because a great deal is tied up in living or dead plant material and in the soil.

Disturbances such as fire and wind make the nutrients stored in trees more available to other trees and plants. Tree harvesting also disturbs the forest. However, it often removes trees and their nutrients from the forest and occurs more frequently than natural disturbances. On fertile soils such as many clay and loam soils the amount of nutrients available often is so large that the quantity of nutrients removed by harvesting is relatively insignificant. On infertile soils, however, harvesting may remove nutrients more quickly than they can be replaced. If nutrients are supplied at a high rate by the soil or by the environment from dust or rain, the impact of nutrient removal through harvesting may be reduced.

Severe disturbance by fire or clearcutting causes a short-term reduction in the demand for nutrients. However, it also increases nutrient supply by increasing decomposition. Until trees and other plants become large enough to use them, many nutrients may be leached away from the forest or at least beyond the reach of tree roots. This may affect not only the forest itself, but also the organisms in streams and lakes receiving nutrients from forest runoff.

You can reduce the loss of nutrients due to tree harvesting in several ways. One is to harvest only the main stem rather than the whole tree. Another is to include prompt reforestation in your harvesting plan and practice.

Forest Health

The term forest health is used by forestry professionals to describe all aspects of forest interactions including biodiversity, nutrient cycling, and insect and disease problems. Since biodiversity and nutrient cycling have already been discussed, here forest health considers the effect of insects and diseases on tree growth and reproduction.

Forest species composition, tree age, tree vigor, and tree injuries all influence how forests are affected by insects and diseases. These factors in turn are influenced by forest management and harvesting.

Tree decline and death often result from the interaction of three factors (Figure 3). These factors are organisms that cause injury or disease, the environment, and tree vigor and genetics.

Figure 3. The disease triangle: The impact of tree disease depends on the individual tree, on living factors (insects, fungi, bacteria, etc.), and on nonliving factors (weather, pollution, human activities, tree injury, soil compaction, etc.).

Insects and fungi are often involved in tree injury and disease. Insects feed on and injure leaves, branches, and roots. Disease-causing organisms infect and grow and reproduce within the tree. The tree responds by producing defensive chemicals or sacrificing infected plant tissue. What we notice as a tree disease results from the combined activity of the infection and the tree's response to it.

Environmental factors include weather, soil compaction, pollution, and logging damage to trees and soil. The environment influences populations of insects and disease-causing organisms as well as tree vigor.

Tree vigor often decreases with increasing tree age and density. This means that vigor can be improved by harvesting old or mature, declining trees (which usually are not old growth) and by thinning. Tree vigor also may be increased by fertilization if nutrients are in short supply.

Many plant individuals and species have inherited the ability to tolerate and resist environmental stress, insects and disease. This underscores the importance of genetic diversity within and among plant species.

Diseases, insect outbreaks, and severe weather are common during the long life of a tree. Vigorous trees can endure temporary stress with minimal effect. Extreme stress such as extended drought may overcome even a vigorous tree's ability to respond. Insects and diseases introduced from other countries often affect trees more severely than native insects or diseases because the trees have no natural resistance.

Timber harvesting can influence forest health by changing forest composition, injuring residual trees, and compacting soil. If logging takes only the tallest, most dominant trees, the remaining trees will be stressed by the dramatic change in light, temperature, and moisture. The remaining trees also are likely to be less fit genetically for that site. Future timber yield and habitat quality may be diminished as a result of this practice.

If residual trees are injured during a harvest, they become susceptible to attack by insects and diseases. Injury also increases the vulnerability of nearby uninjured trees. Soil compaction slows tree growth and creates root injuries that can be exploited by soil fungi.

Tree mortality in a forest is dramatic and may seem to harm habitat, aesthetics, or timber production. However, under many conditions it is expected and natural, and does not indicate loss of forest health. Indeed, trees must die to provide space for other trees, to create conditions for forest regeneration, to provide habitat for birds and mammals, and to return nutrients to rapidly growing and reproducing trees. It is when tree mortality compromises the values we derive from a forest that forest health becomes a concern.

Logging and Forest Regeneration

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Until recently, conservation of forest productivity focused on ensuring adequate tree regeneration following harvest. As we learned more about forests, the values they produce, and the processes and interactions that occur in them, our expectations increased. Today, species diversity and the structure of the forest following logging are important, too.

Successful tree regeneration following harvest is a complex task. Trees' methods of regeneration and growth are important considerations, as is each species' response to harvest. Physical factors such as light, temperature, and moisture also influence regeneration.

Plants, animals, and microbes can affect tree regeneration. Fungi, bacteria, and animals can reduce regeneration by destroying seeds and young trees. Grass, herbs, and shrubs compete with young trees for scarce nutrients and water. Other plants, animals, and fungi may be beneficial by spreading seeds, shading seedlings, or providing nutrients.

How trees regenerate, grow, and react to their environment is the domain of silviculture. Silvicultural characteristics of some trees are listed in Table 1. The principal tool of silviculture is tree harvesting. The best application of harvesting to achieve silvicultural goals requires understanding of both silviculture and harvesting techniques.

Table 1. Silvicultural characteristics of some northern trees

Species	Shade tolerance	Seedling and sapling height growth	Years between good seed crops	Sprouting vigor	Delayed germination ¹
Hardwoods
Paper Birch	Intolerant	Fast	2	Moderate (Small stumps>	None known
Quaking Aspen	Intolerant	Fast	4-5	High (Suckers)	None
Red Maple	Intolerant	Moderate	1	High	Moderate
Sugar Maple	Tolerant	Slow	3-7	Moderate (Small stumps>	Negligible
Basswood	Tolerant	Moderate to fast	1	High	None known
Green Ash	Intolerant	Moderate	Variable	High	Moderate
Black Ash	Intolerant	Moderate	1-8	Moderate	Complete
Red Oak	Intolerant	Moderate	3-5	High	None
Bur Oak	Intolerant	Moderate	2-3	High (Small stumps)	None known
White Oak	Intolerant	Moderate	4-10	High (Small stumps)	None
Conifers
Eastern White Pine	Intolerant	Slow to moderate	3-10	None	Negligible
Red Pine	Intolerant	Fast	3-5	None	Negligible
Jack Pine	Intolerant	Moderate	Variable	None	Limited
Balsam Fir	Tolerant	Moderate	2-4	None	Negligible
White Spruce	Tolerant	Moderate	2-6	None	Limited
Black Spruce	Tolerant	Slow	2-6	Layering (Shoot produced from low branches)	Negligible

¹ Delayed seed germination definitions

None known - All seeds are believed to germinate following dispersal.
None - All seeds germinate following dispersal.
Negligible - Only a small percentage germinate the year following germination.
Limited - A small percentage germinate one or more years following dispersal.
Moderate - As much as 50 percent germinate one or more years following dispersal.
Complete - Most seeds germinate one or more years following dispersal.

From

Burns, R.M. and B.H. Honkela, 1991. Silvics of North America. Volumes 1 and 2. Usda Forest Service.
Harlow, W.M. and E.S. Harrar, 1958. Textbook of Dendrology. 4th ed., McGraw-Hill, New York, N.Y.
Hornbeck, J.W. and W.B. Leak, 1991. Ecology of Management of Northern Hardwood Forests in New England. USDA For. Serv. NE For. Exp. Sta. Gen. Tech. Report NE 159.

Harvesting alters the forest in three principal ways. It changes the understory light environment and climate, it alters understory vegetation, and it disturbs humus and soil on the forest floor. Different harvest methods allow different amounts of sunlight to reach the forest floor and regenerating trees. Clearcutting and seed-tree cutting allow nearly all of the sunlight to reach the forest floor (Figure 4). Shelterwood cutting exposes some areas to nearly full sun while nearby areas remain very shaded. (The sunny and shady spots move as the sun changes position during the day.) Group selection, like clearcutting, provides areas where direct sunlight is available to the forest floor; like a shelterwood cut, it protects forest floor vegetation from the drying effects of the wind. Single-tree cutting creates small openings, allowing little direct sunlight but more diffuse sunlight beneath the remaining canopy.

Clearcutting

Seed-tree cut

Shelterwood

Group selection

Singl-tree cut

Figure 4. Cutting methods: Cutting methods are the cornerstone of silviculture, since they determine what types of tree regeneration are favored.

Increasing sunlight by harvesting increases the temperature of the air, plants, and the soil. Removing trees allows the once-sheltered areas to become exposed to the drying effects of sun and wind. Different silvicultural methods affect all factors of the environment on the forest floor.

The effect of light intensity on growth varies among tree species. Shade-intolerant species grow very rapidly in full sunlight and less so as sunlight decreases (Figure 5). Intermediate trees may grow more slowly than intolerant trees in full sunlight, but their growth decreases less than that of intolerant trees in reduced sunlight. Shade-tolerant trees grow more quickly than intermediate and intolerant species in very shaded environments, but respond less to increased light.

Figure 5. Growth rates: The growth rates of shade-intolerant, intermediate, and shade-tolerant species change with the amount of sunlight. In this chart, aspen represents an intolerant species, white pine represents an intermediate species, and sugar maple represents a tolerant species.

A tree species' ability to succeed in a particular light environment after it becomes established is determined by how well it can grow in that environment relative to other established species. Silviculturists often manipulate light conditions to favor various tree species.

Along with favorable lighting, there must also be a source of potential regeneration. The major sources of natural regeneration are advance regeneration, stump sprouts, root sprouts or suckers, and seeds. Most trees have more than one method of regeneration. The relative importance of each is strongly influenced by conditions following harvest. For this reason, it is important to understand how various harvesting techniques affect regeneration.

Advance Regeneration

Seedlings present at the time of harvest are known as advance regeneration. These are usually shade-tolerant or intermediate species. Harvesting operations can damage advance regeneration. Most seedlings, especially those of conifers, do not readily recover from logging damage. However, some hardwood trees such as oak will sprout from the base of a broken seedling.

Tree and shrub advance regeneration is present in the understory of most forests (Figure 6). Small shrubs and trees are sparse or absent when the understory is shaded by a dense canopy. As the forest ages and individual trees die or lose large branches, small gaps develop in the canopy and shade-tolerant understory trees and shrubs respond by increasing in abundance and height.

Figure 6. Canopy and understory: Dominant trees (D) are the tallest and have the best access to sunlight. Codominant trees (C) form the majority of the canopy; only their tops are exposed to direct sunlight. Intermediate trees (I) still have limited access to direct sunlight. Suppressed trees (S) are completely overtopped. Advance regeneration and shrubs (ARS) form the understory, increasing in height and number in response to gaps in the canopy.

When the stand becomes so old that larger gaps form, shade-tolerant tree and shrub species may form another canopy beneath the tallest tree canopy. Most trees in this understory canopy are so well-adjusted to low light that their ability to adjust to increased light is limited. Harvesting that removes only large, merchantable trees from the canopy often leaves trees that have developed in these low-light conditions. Such trees may grow slowly for several years before they become accustomed to the new conditions.

Sometimes light, moisture, and seedbed conditions in forests are so favorable for establishment and growth of advance regeneration that it develops readily. Spruce and fir advance regeneration develops readily under aspen because the canopy is relatively sparse. In forests with more dense canopies, advance regeneration only develops in canopy gaps caused by tree death, wind, low-intensity fires, or selective cutting.

By protecting advance regeneration during harvest you can gain several years toward the development of the next mature forest. Advance regeneration also maintains shade-tolerant and intermediate tree species, which would be less abundant following clearcutting. When incorporating advance regeneration into a logging plan:

Understand how tree seedlings grow and compete with other plants and respond to new conditions after harvest.

Include alternative sources of regeneration (seeds, sprouts, or planting) for areas in which advance regeneration is inadequate.

Confine logging traffic to the smallest possible area with the use of designated trails for felling and skidding.

Stump Sprouts

Stump sprouts are an important source of regeneration in many hardwood stands because most hardwood trees produce them. Maples, ashes, birches, basswood, and oaks are particularly prolific producers of stump sprouts. In many hardwood forests that were once logged, the trees that are dominant today sprouted from stumps of harvested trees. No conifer species native to the northeast or north-central regions of the United States can produce stump sprouts.

Regeneration from stump sprouts results in clumps of several stems that gradually thin with age through natural mortality. Sprouts can grow more rapidly than seedlings of the same species because they use food reserves, water, and nutrients provided by the roots of the parent tree.

Since sprouts can develop from the stump, the condition of the stump is important. Flat, short stumps produce the best sprouts (Figure 7). (Note, however, that the method of felling is not important; sprouts will grow from stumps that are either sawn or sheared.) Also, more energy is available to produce sprouts if trees are harvested when they are dormant rather than during the spring or summer. The production of stump sprouts often decreases with increasing stump diameter and tree age.

Figure 7. Stump sprouts: Stump sprouts that originate from high stumps have poor quality first (butt) logs, and the sprouts become unstable as the parent stump rots away.

When mature forests are logged, stumps generally are widely spaced so the resulting stump sprouts cannot occupy all the available space. Thus, stump sprouts can seldom be relied on as the only source of regeneration. When incorporating stump sprouts into a logging plan:

Cut stumps flat and close to the ground.

Avoid excessive damage to stumps from skidding or other activities.

Evaluate the potential for stump sprouting by considering tree species, tree age, stump diameter, and density and condition of small-diameter trees likely to produce the most sprouts.

Harvest during the dormant season when possible.

Root Sprouts or Suckers

Root sprouts or suckers are new growth that originates from roots. Even small numbers of beech or aspen in a forest can produce many suckers. Sweetgum, black locust, and balsam poplar trees also produce root suckers. Energy stored in roots enables sprouts to grow more quickly than other vegetation after harvesting or fire. Root sprouts can occupy more of the area than stump sprouts because roots are more widely dispersed.

Pure aspen forests often produce more than 20,000 suckers per acre the year after clearcutting. As a result, clearcutting often increases the abundance of aspen in mixed species forests, especially if it removes seed sources or destroys advance regeneration of other species.

The ability of aspen to produce suckers is controlled by the presence of healthy aspen trees. As few as 55 healthy, mature (eight-inch diameter) aspen per acre, if they are widely distributed, can provide adequate regeneration. The presence of residual trees may reduce abundance and growth of aspen suckers.

Rutting (depressions caused by repeated machine traffic) reduces suckering by damaging the shallow aspen roots. Suckers often will be absent from rutted areas. The more ruts there are per unit area on a logged site, the more likely it is that suckering failure will occur.

When incorporating aspen suckers into a logging plan:

Minimize the amount of area rutted, since rutting damages roots.

Avoid harvesting when the soil is very moist because aspen roots are injured by excess soil moisture, and rutting is more frequent on moist soils (winter harvest may be necessary on poorly drained soils).

Begin harvesting at the back of the area to be logged and use designated skid trails to avoid skidding over previously logged areas.

Seed Regeneration

Regeneration from seed is very complicated due to differences among tree species in seed production and germination. Mature trees produce and release seeds at various times during the growing season (for example, silver maple seeds mature in early spring while pine seeds are not released until late summer and early fall). Also, seed production is not consistent from one year to the next for many species. Red oak, for instance, produces a good seed crop only once every three to five years. As a result, the timing of disturbances such as harvesting may favor certain species.

Seeds are disseminated mainly by wind, water, animals, or gravity. The means of dissemination determines seed contribution to logged areas. Many wind-disseminated seeds can be scattered up to 300 feet by prevailing winds. Openings of less than five acres can easily be supplied with wind-disseminated seed from the surrounding forest. Much larger areas can receive seed if they are narrow or irregularly shaped or if scattered residual trees are left to provide seed.

Gravity- and animal-disseminated seeds are typically larger than wind- disseminated seeds and without assistance they will not travel far from the parent tree. Animals often will transport seeds long distances, but the seed supply is greatest near the parent tree. Parent trees should be uniformly distributed to provide an adequate seed supply to harvested areas.

Most seeds lose viability if they don't germinate within a year after they fall. However, seeds of raspberries, cherries, and a few other species can be stored in the leaf litter on the forest floor until conditions become favorable for germination. When the forest canopy is disturbed by logging, these seeds germinate. Because of this capability, the current year's seed supplies may be unimportant to the regeneration of these species.

Seeds must land on a suitable seedbed to germinate. Seedbed requirements vary among tree species. A suitable seedbed provides stable moisture and temperature. On the forest floor, mineral soil and decomposed organic matter help retain moisture and buffer temperature changes. Natural disturbances such as forest fires expose mineral soil over large areas. Winds and storms expose small areas of mineral soil when trees are uprooted. In wet or humid environments, decomposed organic material such as an old log makes a good seedbed because it retains moisture and allows for root development.

You can improve seed germination and seedling establishment by controlling competition from herbs, grasses, and shrubs. Exposing mineral soil can help remove competing vegetation as well as create a seedbed. Management guides for individual species produced by state extension services and the USDA Forest Service provide information on seed dissemination and germination requirements of individual species.

When incorporating seed regeneration into a logging plan:

Evaluate potential seed contributions from residual trees, the surrounding forest, and the forest floor by considering species, dissemination methods, prevailing wind direction, and distance between the logged area and seed source.

Use harvesting methods that maximize the area of seedbed (mineral soil or decayed organic matter) best suited to the preferred tree species, or plan to prepare the seedbed following harvest.

Logging Methods

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There is no single "right way" to harvest an area. Because every forest is different, it is impossible to make recommendations without an inventory of the forest, a clear understanding of the landowner's short- and long-term objectives for income and forest condition following logging, and an understanding of local tree species and their silvics. Unless the landowner's goal is to convert the area to a land use other than a forest, it is important to develop and implement a forest management plan before you harvest. The harvest should then include practices that ensure forest productivity and promote regeneration by protecting residual trees and advance regeneration, preparing the seedbed, and minimizing soil compaction.

To protect residual trees:

Minimize turning and curves when planning skidding trails. Locate skid trails to accommodate future as well as current harvests.

Consider the dimensions of logging equipment when planning trails. Large skidders (Figure 8) are often more than nine feet wide and may need several feet on either side to operate without difficulty. Felling machines also require extra space to operate efficiently.

Figure 8. Cable skidder

Designate bumper or rub trees next to trails to protect residual trees, especially at curves and turns in the skid trail (Figure 9). Remove bumper trees at the end of the harvest.

Figure 9. Bumper trees: Bumper, or rub, trees prevent damage to trees that are to be reserved. Use low-quality trees or trees scheduled for removal as bumper trees. In most cases damaged bumper trees, especially conifers, should be removed at the end of the harvest.

Avoid logging when soils are very moist. This prevents root damage, reduces compaction, and reduces the chance that residual trees will be damaged by sliding machines.

Take special care to avoid contacting trees during the growing season, when bark is loose and easily damaged.

Use forwarders rather than skidders where possible (Figure 10). They are shorter when loaded and can maneuver more easily through residual trees.

Figure 10. Forwarder

To protect advance regeneration:

Designate specific skid trails to reduce trail density and to control the path of skidders and forwarders.

Designate turning areas on skid trails so skidders and forwarders maneuver on the skid trail and not in the stand (Figure 11).

Figure 11. Advance regeneration cutting methods: Protection of advance regeneration requires several complementary logging techniques.

Don't operate when it's so wet that skid trails become impassable and skidders and forwarders are forced to take alternate routes. You may be able to extend skidding when soils are moist by using high-flotation skidders or forwarders or by padding the trail with slash to distribute the load and decrease rutting.

Use cable skidders rather than grapple skidders to reduce maneuvering in the logged area. A cable skidder can remain on the skid trail and reach felled trees with little maneuvering.

Reduce damage from skidding by felling trees so bunches of trees are close to the trail and felled at a 45 degree angle to the trail.

Use a shortwood system with a forwarder and possibly a feller-processor (Figure 12) to reduce contact of felled trees with the understory and soil. A feller-processor places wood in piles on either side of its path, so the forwarder can use the same path as the feller- processor.

Figure 12. Feller-processor

Be aware that deep snow when harvesting will help protect advance regeneration.

To prepare mineral soil seedbed:

Remember that skidding usually disturbs soil more and creates potentially more exposed mineral soil seedbed than forwarding. Trees are dragged across the logged area and skidders, especially grapple skidders, must travel over more of the area to maneuver and gather felled trees.

When soils are dry or sandy and not sensitive to compaction, random skidding will create more disturbed seedbed areas. During random skidding the skidder takes a unique path to the landing or to a main skid trail after each load. Avoid turning random skidding into a network of unplanned main skid trails. This results in greater soil compaction and little increase in soil disturbance.

To minimize soil compaction:

Designate skid trails to reduce trail density and control the path of skidders and forwarders. This is especially important when soil is moist and easily compacted.

Use high-flotation equipment on moist soils. This will limit compaction where equipment travels a few times and prevent main skid trails from becoming impassable.

When possible, operate logging equipment on soils that stay moist throughout the growing season only when they are frozen.

Consider starting logging at the back of the stand and using designated skid trails to the landing. This technique a) prevents skidder and forwarder operators from using alternate routes to the landing; b) prevents the need to cross previously logged areas and injure regeneration if logging is delayed; c) allows trees to remove soil moisture from the area not yet logged, resulting in easier felling and skidding; and d) allows tree cover to retain snow and frost on the ground longer, resulting in easier felling and skidding.

Conclusions

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Our knowledge of forests and of how people value forests is continually increasing. This has resulted in an expanded view of the importance of maintaining forest productivity. We now know that to sustain forest productivity it is important to protect soils, to maintain forest cover, and to preserve the links among living and nonliving components of a forest. It also is important to consider how timber harvesting will affect biodiversity, nutrient cycling, and forest health.

Timber harvesting practices must maintain forest productivity and promote successful regeneration. This requires protecting residual trees and advance regeneration in partial cuttings, preparing the mineral soil seedbed, and minimizing soil compaction. The specific recommendations provided above will help address those needs.

It's important to develop a forest management plan before any timber harvest occurs. The plan should clearly describe both short- and long-term management goals of the landowner. It also should consider how to maintain forest productivity.

Seek the advice of a professional forester to ensure that each harvest satisfies your management objectives and maintains the forest in a vigorous and productive condition. A signed, written contract between the landowner and the logger is recommended for any timber sale. The contract should incorporate a process for appropriately protecting resources. A professional forester can help develop and administer a timber sale contract.

Glossary

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Bumper or rub tree – A tree in a partial cut whose position next to the skid trail will protect the residual trees from damage.

Canopy – The layer formed by tree crowns as they grow together. The canopy excludes much of the sunlight from the forest floor.

Conifers – Plants that bear seeds in cones (e.g., pines, firs, spruces, cedars, redwoods, cypresses, junipers, hemlocks, and larches).

Dominant – A tree that occupies a position in a forest where its crown is nearly completely exposed to sunlight.

Ecology – The relationships of living organisms among each other and with their nonliving environments.

Feller-processor – A machine that combines felling with one or more other functions, typically delimbing and bucking.

Felling – Separating the tree from the stump near the ground, usually with an axe, chain saw, or specialized machine.

Forwarder – A machine commonly used with a shortwood system that transports wood in the forest while completely supporting it.

High flotation – Equipment that has a ground pressure of less than five or six pounds per square inch (psi). Less than four psi may be needed to operate on swamps without difficulty.

Landing – Area on a harvested site where wood is transferred from the skidders or forwarders to trucks for road transport. In some operations the trees are processed or stored on the landing before transport.

Residual tree – Any tree not harvested within a harvest area.

Shear – A method of felling trees in which the tree is severed by sharp, flat plates mounted on a machine.

Shortwood system – A harvesting system in which the tree is felled, delimbed, and cut into short lengths before it is hauled to the landing (usually by a forwarder).

Silvics – The combined characteristics of growth and reproduction of trees.

Silviculture – The art and science of managing forest vegetation to produce desired future forest conditions.

Skidder – A machine that transports wood in the forest by supporting it at one end and dragging the other across the ground.

Slash – Stems and branches remaining on the ground after logging.

Species – A group of organisms that are isolated geographically or that are similar in genetics, appearance, and habits and that form an independent population.

Susceptible – Having a weakened ability to defend against disease or insect attack due to environmental conditions, genetics, or growth stage (e.g, seedling, sapling, or mature tree).