LESSON 4: SILVICULTURE

The science of forestry is based on understanding natural processes and using the same concepts to manage the forest for whatever benefits are desired. Applying these concepts is called silviculture from the Latin words silva (forest) and cultura (cultivation, husbandry). A good working definition of silviculture is "the art and science of managing a forest."

In some ways, forestry is like farming; it just takes a lot longer for the crop to mature. Like farming, there are many intermediate steps between the decision to grow trees and the harvest.

When a farmer sets out to grow a crop, the first decision he must make is what crop to grow. This will be based on a number of considerations: what crops are suitable for his land, what materials and services are available to support his effort, what markets are available, etc. He must also decide how to finance his operation, evaluate potential problems, and finally decide if his profit from the enterprise is worth the risk and expense.

Once the decision is made, the farmer begins to implement the plan. He must prepare the land, purchase and apply fertilizer, purchase and plant the seed, cultivate the crop, protect the plants from insects and diseases, irrigate and apply supplemental fertilizer if needed, monitor the progress of the crop, harvest it, and market the final product.

Like agriculture, silviculture consists of a number of individual activities. These individual activities are referred to as cultural practices. Many cultural practices may be involved over the life of the forest.

Getting a stand of trees established includes the cultural practices of site preparation and regeneration. Site preparation is anything needed to get the land ready for growing a new forest. It may be very simple like burning off brush and debris, or it may involve the use of heavy equipment to completely clear the land.

Regeneration is actually establishing new trees on the site. This may be done by planting tree seedlings, sowing tree seed, or making it possible for nature to regenerate the forest through natural seeding or sprouting.

Any crop must be cared for while it is growing, and trees are no exception. While it is usually impractical to fertilize, irrigate, or cultivate a forest stand, the manager must insure that the trees are protected and that their basic growth requirements are met.

The forest must be protected from wildfire, insects, diseases, and the abuses of uncaring people. Fire protection may include establishing a system of permanent firebreaks around and through the forest stand. Prescribed burning (discussed later) is also an excellent fire protection measure in some pine stands.

Insect and disease protection is a bit more difficult; spraying an entire forest stand for insects is generally too expensive and trees can't be immunized against disease. Since vigorous trees are much less susceptible to insect and disease attack, the best protection is to keep them growing well. If insect or disease attacks occur, the most practical treatment is to remove the affected trees.

Sometimes forest managers are confronted with problems caused by people. A lot of people have no understanding or respect for the forest, so they use the forest as a dumping ground for trash and household debris. Others may abuse the forest through unauthorized hunting, misuse of recreational vehicles, etc. This explains why many timber owners have had to block roads into their forests and post "No Trespassing" signs.

Many people might seriously doubt the judgment of a forest manager who intentionally sets fire to the woods. Actually, this can be an extremely effective cultural practice for southern pines if handled by professionals. Such professional burning is called prescribed burning because it is carefully planned and executed under exacting weather conditions to achieve a specific purpose. Some of the uses of prescribed fire in South Carolina are:

Site preparation:

Sometimes fire is all that is needed to prepare land for planting or seeding. Prescribed burning may be very effective on sites with light brush, grass, or logging debris. Usually a fairly hot, fast-moving fire is prescribed. Burning can also be used to prepare the site for natural reseeding. The fire removes much of the organic litter on the forest floor, allowing seeds to fall directly on the soil.

Disease control:

Fire may be prescribed to control brown- spot needle disease in longleaf pine seedlings. A hot, fast-moving fire consumes the needles, killing the fungus that causes brown- spot disease. Since longleaf pine is extremely fire tolerant, the seedlings survive to produce new disease free needles.

Brush control:

The presence of hardwood brush in pine stands can reduce the amount of water and soil nutrients available to the pines. A low-burning, low-intensity fire will kill the heat-sensitive brush back to the ground without harming the more fire tolerant pines. This process will have to be repeated every few years since the brush will sprout back from the roots.

Wildfire hazard reduction:

As dead needles and twigs fall from trees, they decay and return nutrients to the soil. Frequently, pine stands produce this organic litter faster than it can decay, resulting in a buildup of highly flammable material on the forest floor. Carefully administered prescribed fire can be used to safely remove this excess, reducing the danger from damaging wildfire.

Wildlife habitat improvement:

Early farmers knew that burning caused the woods to "green up" and frequently set fires to improve browse for their livestock. Tender, succulent hardwood sprouts and herbaceous seed-bearing plants proliferate after prescribed burning, thus improving the food supply for deer, rabbits, quail, songbirds, etc.

Some wise philosopher once observed that "nature abhors a vacuum." In practical terms that means that any patch of ground usually grows as many plants as it can support. In the case of trees, the larger they grow, the fewer the land can support. If left alone, the overcrowding will take care of itself as less vigorous trees gradually die out. While the process is taking place, the entire stand grows slowly and the trees that die are simply wasted.

Forest managers can make this natural process more efficient by harvesting some of the trees periodically. A harvest designed to provide more room for trees to grow is called a thinning; a harvest which seeks to remove diseased, suppressed, and malformed trees is called an improvement cut. Most of the time these are combined so the harvest can serve both purposes.

When the manager selects trees for cutting, they are usually marked with two spots of paint. One spot is about eye level so the logger can easily locate the trees that are to be cut; the other is at the base of the tree, below where the logger will cut. This spot remains on the stump, providing the manager a way to verify that only the selected trees have been harvested.

Thinnings and improvement cuts provide for the biological needs of the forest (available space, light, soil nutrients) as well as the needs of man. Since such harvests are usually scheduled when the trees are large enough to be useful, the landowner receives income and the forest products industry obtains raw material for manufacturing.

Thin this stand

Make copies of the exercise "Too Many Trees" and have the students mark the trees that should be cut. Discuss their choices. Is the forest still well-stocked? Do the remaining trees have plenty of room to grow?

Talk about the individual trees. Why should this one be cut? Why should that one be left? Students should be able to justify their decisions.

Assuming this is a pine forest (intolerant), most trees are probably about the same age. Should the small trees be cut? (Yes) Why? (Their growth may be stunted due to overcrowding or they may be of poor genetic quality. Either of these reasons could explain why they aren't as large as the others.)


Reference Resources / Education

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