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Forest Stewardship Principles

LESSON THREE - FOREST RENEWAL

How trees are harvested affects the type, amount and the method by which young trees become established. For example, clearcutting a white pine stand could result in hardwoods becoming established. However, if seed trees are left, chances increase that young pine seedlings would become established. The young trees that establish on the forest floor are known as regeneration.

In order for timber harvesting to be sustainable we must ensure a future crop of commercial trees. Therefore it is important to give some thought to how you are going to establish a future crop after a harvest operation. The easiest way to manipulate what will come back after a cut is through the harvesting system. A harvesting system is simply a way or method to harvest and renew the forest. A harvesting system requires consideration on how to regenerate the future stand before harvesting actually takes place. Harvesting systems follow 4 basic types:

  • clear cut
  • shelterwood cut
  • selection cut
  • high grade cut

There are variations on each of these types, for example patch clear cut. Each system and its variations are designed to facilitate renewal with specific stand types and conditions. For examples shelterwood harvesting works well in mature white pine stands, but does not work well in young white birch stands.

High grade cutting is the only system which is not recommended. High grading involves harvesting the best trees and leaving the poor quality, diseased, dying and suppressed trees. This usually results in the poor quality trees reproducing the next generation and as a consequence a poor quality forest for the next harvest.

This manual will give a brief overview of the different harvesting systems and in what situations they are best applied. For more information see the reference list at the end of this chapter.

Clearcutting

The harvest of all trees from an area of forest land in a single cut is a clearcut. The assumption is that a new even-aged stand will be established. This can be through artificial (planting) or natural means. Research has shown that two-thirds of clearcuts in Nova Scotia regenerate naturally. In some cases clearcutting, followed by planting, is the only reasonable option. For example, old field white spruce seldom regenerates itself.

In general, stands best suited for clearcutting are even-aged mature or older stands that have species that regenerate after a disturbance, e.g. red pine, balsam fir, aspen, and white birch. Other stands to consider for clearcutting are stands with a high percentage of dead or unhealthy trees. If there has been extensive fire, wind, or insect damage you may want to consider clearcutting. Other stands to clearcut are stands that are susceptible to blowdown such as when they are on ridgetops or in poorly drained areas. Also stands with tree species that are short-lived or unable to grow in the shade could be clearcut.

Variations on clearcutting can be done to increase the chance of desirable regeneration establishing. Some examples are patch, strip and seed tree clearcuts.

Shelterwood Cutting

Shelterwood cutting involves a gradual removal of the over story to develop desirable natural regeneration. This system allows some sunlight to reach the forest floor which promotes the germination and growth of seedlings. The over-story provides seed and shelter for the seedlings.

Shelterwood harvesting should be done in healthy even-aged mature stands that are windfirm. At least 30% of the trees in a stand should be shade tolerant species e.g. red spruce, eastern hemlock, white pine, yellow birch, sugar maple, white ash, red oak.

From Home Study Module 2: Harvesting Systems

Selection Cutting

Selection cutting involves a continuous harvest of trees without removing the over-story. A proper selection cut will involve the removal of poor quality, mature and over mature trees. As well, thinning is often done on immature trees. The openings created from the harvested trees provide space and sunlight for new trees to establish. In this way the stand continually renews itself. The process results in an overall improved condition of the stand.

Selection cutting is not appropriate for all stands. Short-lived trees that don't grow well in shade are not suited for this type of harvest (white birch, aspen, balsam fir, eastern larch). Trees that are long-lived and can grow in shade are best suited for selection cutting (red spruce, eastern hemlock, white pine, red oak, sugar maple, yellow birch, white ash). If there are several age classes in the stand ( e.g. seedlings, poles, mature) the stand is ideal for selection cutting. If selection cutting is done on an even-aged stand it will eventually become uneven-aged.

References

  • Woodlot Home Study Course: Module 2 Harvesting Systems. Nova Scotia Department of Natural Resources.
  • Woodlot Home Study Course: Module 5 Stand Establishment. Nova Scotia Department of Natural Resources.
  • Shelterwood Harvesting Manual. By R.G. Robertson & R.W. Young. Nova Scotia Department of Natural Resources

Exercise 3. Forest Renewal

1. Using the table below write in the treatment section a proposed harvesting system for stands 3, 4 and 5 on the I.M. Ready woodlot. Decide what harvesting system will best facilitate renewal based on what tree species are present. Assume that there is no visible regeneration right now. Mature stands are stands that have reached their maximum volume, while overmature stands are losing volume and likely contain dead or dying trees.

answers