LESSON 5: SILVICULTURAL SYSTEMS

This lesson provides a brief overview of the long-term planning for managing a forest stand. The descriptions of silvicultural systems are provided as general examples; many variations are possible within each system. Keep in mind that silviculture is both an art and a science, and different managers will take different approaches to any management scenario.

After the lesson material has been discussed in the classroom, arrange with a local forest industry, consulting forester, or the Forestry Commission for a field trip to see some of these practices in your area.

When a series of cultural practices are planned into the long-term management of a forest stand, the total program is called a silvicultural system. Planning a system depends on the objectives of the owner, the tree species involved, and the land itself.
For example:

. . . High, rocky land in the mountains would not be suitable for growing bald cypress; deep swamp in the coastal plain will not support white pine.

. . . An owner whose primary objective is a rapid return on his investment might want to grow only pine pulpwood; another landowner whose objective is to produce high-quality, high-value sawlogs would plan to maintain his forest for a longer period.

. . . The practices of prescribed burning and regular thinning are appropriate in southern pine stands, but are not usually recommended for hardwood stands.

Since the regeneration of the stand is of such importance, silvicultural systems frequently take the name of the planned regeneration method. Three systems frequently used in South Carolina are the seed tree system, the artificial regeneration system, and the coppice system.

Seed Tree System:

Used mostly in pine stands, this system involves a specialized program of timber harvesting and prescribed burning to imitate the natural pine regeneration process.

One of the first things a manager does is decide how long he wants to maintain the stand. This decision is based on the tree species, economics, and the owner's objectives. The length of time between establishing the stand and the final harvest is called the rotation or rotation age.

In the early life of the stand, a seed tree system is just about the same as any other type of pine management. The stand will be protected from wildfire, insects, and disease; thinning/improvement cutting will be done; and prescribed burning will probably be conducted every 3-5 years.

About five years before the end of the rotation, prescribed burning is done more frequently. This keeps brush growth to a minimum and begins to expose patches of mineral soil on the forest floor, creating a good environment for seed to germinate and grow. On every acre, 10-12 of the very best trees are selected and clearly marked. These are the seed trees which will become the parents of the new forest.

When the rotation age is reached, all trees are harvested for market except for the seed trees. The seed produced by these remaining trees are scattered by the wind and begin to grow. When enough young pines are established to adequately restock the forest, the seed trees are harvested and the cycle begins again.

Seed trees

Project the graphic "Seed Trees?" onto a screen or reproduce it on the chalkboard. Ask the children to discuss which trees would obviously not make good seed trees (Numbers 3,5,7,9 and 11 seem to be good trees, but aren't very tall. This may be because of some genetic weakness. Numbers 2, 8, and 13 are crooked and malformed. Number 12 appears to be stunted.)

Ask the children to evaluate and compare the good trees, then ask them to select the two trees best suited to reseed the area. 

Artificial Regeneration System:

This system is also used most frequently in pine management. The basic cultural practices (protection, periodic harvesting, and prescribed burning) are similar to those described for the seed tree method. The big difference, once again, is in how the stand is regenerated.

Under the artificial regeneration system, when most of the trees are ready for harvest, the entire stand is cut. This is commonly called clearcutting. Some type of site preparation is usually needed following a clearcut. This may be done by prescribed burning to get rid of logging debris and brush, by herbicide to kill unwanted plants, or by clearing the land with heavy equipment. The site preparation method depends on the condition of the site and the planned method of regeneration.

When site preparation is complete, a new forest is established by planting tree seedlings or sowing seed across the land. In South Carolina, the most common method is planting seedlings because it allows the manager to control the spacing between trees. Another advantage is the option of planting genetically improved seedlings which grow faster and are more resistant to disease.

Ask the children when they think would be the best time of the year to plant trees. Most will probably say spring or summer.

People tend to think of planting as being done when the weather warms up in the spring. Unlike ornamental trees or shrubs, forest tree seedlings are most frequently available as "bare root" plants. This means that they do not have a ball of soil around the root system. Because of this, forest plantings are generally done during the winter and early spring. This allows the seedling to become acclimated to its new environment before the growing season, reducing the biological shock of transplanting.

Coppice System:

By definition, a coppice is "a forest originating mainly from sprouts or root suckers rather than seed." Most hardwood species in South Carolina sprout readily from cut stumps making this a viable means of regenerating hardwood stands.

When a hardwood tree is cut, dormant buds beneath the bark of the stump are stimulated. New sprouts grow from these buds, frequently resulting in a clump of new trees all coming from one stump. These new sprouts grow rapidly because they are still served by the large root system of the parent tree.

There are many variations of the coppice system. The most basic method is to simply clearcut a hardwood stand and allow nature to take its course. Another method is to clearcut and wait for sprouts to appear, then remove all but one healthy sprout from each stump. Others involve even more intensive management, including treating competing brush species with herbicide or clearcutting many small patches instead of the entire stand.

One method being practiced in South Carolina is the silvicultural clearcut. This involves a normal clearcut of all usable timber followed by another cutting that levels brush and any worthless timber remaining on the site. This method allows all sprouts equal access to sunlight. Given an even start, sprouts from the large timber stumps will grow more rapidly and quickly establish dominance over the brush.


Reference Resources / Education

Contents / Lesson 1 / Lesson 2 / Lesson 3 / Lesson 4 / Lesson 5 / Lesson 6