Forestry is a science.
The Science of Forestry A Quick Lesson in Silvics & Silviculture
One of the most important of the many disciplines in forestry is silviculture. Silviculture is the agriculture of trees -- how to grow them, how to maximize growth and return, and how to manipulate tree species compositions to meet landowner objectives. To understand silviculture, one must first understand silvics. Silvics involves understanding how trees grow, reproduce, and respond to environmental changes.
When considering forestry legislation, the impact of proposed regulations on silviculture must be determined to avoid any unintended consequence. The understanding of both the silvicultural requirements for the forests and of the effect of regulations on silvicultural methods, is of prime importance to anyone wishing to promote healthy, growing forests for future generations.
Here is a quick lesson on silvics.
Some tree species thrive in shade -- sugar maple, beech, hemlock, dogwood, red maple and basswood are good examples. These species can live, grow, and reproduce in shade and semishade conditions. Many tree species prefer or require full sunlight -- yellow-poplar, walnut, some oaks, loblolly pine, and hickory are good examples. These species require full sunlight to reproduce, after which they grow best in full sunlight or as part of the overstory canopy of the forest. They also tend to be the fastest-growing species and, to a great extent, the most valuable species. Still other species such as white pine, white ash, and some oaks, are intermediate in their sunlight requirements. You may have noticed these patterns in the woods.
Silvics also is concerned with seedling requirements, elevation, and location. Different species will show up in different areas, on different soils, and at different elevations. If this sounds like ecology, then it can be stated accurately that silvics is the ecology of the forest.
Silviculture involves managing and handling the forest in view of its silvics.
Silviculture imitiates a natural change -- such as a windthrow, beetle infestation, or fire. However, silvicultural methods harvest forests products for human use rather than wait on nature to burn them, eat them, or blow them down. Silviculture can be practiced at any time in the life of a timber stand. Southern pine management is an excellent example of silvicultural treatments throughout the life of a stand. However, in Appalachian hardwoods, 90 to 100% of silviculture is decided and carried out at the time of a timber harvest.
Perhaps it is worthwhile to mention what silviculture is not. "High-grading" a timber stand is not silviculture. High-grading is "taking the best and leaving the rest". Silviculture looks not only at the timber crop currently available, but also at the effects of present day harvesting on the next timber crop. Foresters are in a unique business in that they commonly make management decisions that will affect crop quality and growth many years into the future.
The following are a few silvicultural harvesting methods:
Selection systems
Selection systems are partial removals of trees based on the silvicultural objectives of the landowner. This method is used in uneven-aged stands, usually those that are hardwoods, when species of shade tolerant or intermediate tolerance are considered desirable. Each tree is assessed, determined to be cut or left, measured, tallied, and marked. Although economics always plays some part in determinations, it is not the only factor. Rate of growth, potential for further growth, health, quality, spacing, and species are some of the factors that also must enter each determination.
It is important that a landowner get a graduate forester to do this assessment. A thinning based only on economic factors can easily become a high-grade. Furthermore, a small tree is not always a younger tree. Although many small trees in the woods are that size because of their youth, just as many are small because of poor genetics, stunted growth, or being a poor or inappropriate species for the site. It takes many years of experience to tell the difference.
Part of this method is manipulating the amount of sunlight on the ground to successfully regenerate desired
species. Selection system harvesting has the advantage of allowing a timber stand to retain its forested appearance in the years immediately following harvest. It has particular advantages in higher elevations and farther north where shade-tolerant species are considered very desirable. It has disadvantages of providing for slower long-term growth, for allowing undesirable species to predominate, for allowing undesirable epicormic branching on future crop trees, for holding back valuable sun-loving species, and for being an easily and frequently abused method. Further more, it is very difficult to use successfully on steep ground due to high potential for heavy logging damage on residual trees.
Thinning in pine stands, which are more typically even-aged, is designed to remove the smaller, deformed, or too closely spaced trees. The remaining trees are then able to receive sufficient light, moisture and nutrients to grow to valuable size.
Selection system harvests can be designed to suit each individual tract, each site, each timber type, and each individual landowner. Each type of selection system has a separate set of objectives for the manipulation of sunlight, reproduction, present crop, and future crop.
Seed Tree CutsSeed tree cuts allow the harvest of all trees except 2 to 10 trees per acre. These remaining trees are chosen for their good form, genetics, species, and ability to produce seed crops. The job for these remaining trees is to rain down genetically good-quality seed on the freshly disturbed areas. The method is used far more frequently in pine stands then in hardwood stands.
ClearcuttingClearcutting is also a silvicultural method. This much-embattled method is truly a valuable silvicultural practice. Clearcutting is most often prescribed where sun-loving species are desired for the future timber stand. It is also prescribed in poor-quality or problem stands which have been abused by fires or repeated high-grading. In pine management, a clearcut is followed by planting seedlings if natural reproduction does not occur. However, where quality hardwoods grow, natural regeneration supplies more than enough seedlings from existing seed, existing seedlings, root sprouts, and stump sprouts. Thankfully, natural regeneration of hardwoods is one of nature's strongest and most inevitable forces in our region. Where desirable hardwoods can be grown, natural regeneration is the proper plan; attempting to plant or artificially regenerate in such an area is neither necessary, wanted, nor advisable.
The desired effect of a clearcut is to start all regeneration at ground level so that the resulting timber crop is made up of desirable sun-loving species, which are the fastest growing, straightest, healthiest, and most superior trees possible. A 20- to 60-year-old clearcut is a textbook case of survival of the fittest. Because full sunlight is provided for future crop trees, rate of growth is at its greatest. Clearcut areas show 1.5 to 2.0 times the growth rates per acre than in selectively cut areas.
Clearcutting is not "cutting everything we want." A clearcut should truly be a clear cut. . The objective is to provide full sunlight -- not partial sunlight with a heavy dose of shade from runt, cull, and unwanted tees.
Remember, the choice of silvicultural method must be based upon the silvics and characteristics of the existing species in a stand and upon the species deemed desirable to grow in that future stand. There are many silvicultural methods and these are only some of the ones which apply specifically to harvesting. Each method has its place in different areas, in different terrains, on different soils, in different timber types, and with different landowners.
To learn more, contact the Maryland Forests Association at P.O. Box 599, Grantsville, MD 21536, mdforests@hereintown.net or 301/895-5369.
Note: Information for this piece was derived from the article " Silvics & Silviculture - The Agriculture of Trees" by Registered Consultant Foresters Kevin Belt and Robert Campbell for the West Virginia Farming & Forestry Bulletin of the WVU Extension Service.
