A major portion of the practice of forestry silvicultural systems are timber harvesting methods designed to ensure successful and succeeding forest stands for the future. Without the application of these methods of reforestation, there would only be random tree stocking of both preferred and non-preferred species leading to major shortages of wood and trees demanded by the consumer. Nature, when left alone, uses its time-consuming natural process of reforestation and is appropriate in many situations. On the other hand, foresters may need to manage for a forest's best use when forest owners and managers need reliable income and other necessities in an appropriate time frame.
Many of the accepted forest regeneration concepts were first introduced to North America by German forestry professors during the late 19th Century. Germany had practiced these forest reproduction schemes for centuries and one of the earliest books on the subject was written by German forestry pioneer Heinrich Cotta during the late 17th century. These western European educated "foresters" were first to define the profession of forestry and became overseers of the training of foresters who managed large forest tracts owned by kings, aristocrats and the ruling classes.
These imported tree reproduction systems have continually evolved and developed into what are now used today. They are separated into "classifications" and used throughout the world where the practice of forestry and forest management is necessary to encourage sustainable forests. These classifications are conducted in logical sequence and the steps lead to healthy, well stocked forests for future generations.
The Classification of Tree Reproduction Methods
Although there are innumerable combinations, for simplification I will list the six general reproduction methods listed by silviculturist D.M. Smith in his book, The Practice of Silviculture. Smith's book has been studied by foresters for decades and used as a proven, practical and widely accepted guide at the point where a timber harvest is necessary and where natural or artificial regeneration is the desired replacement.
These methods have traditionally been called "high-forest" methods which produce stands originating from a remaining natural (using a high or aerial) seed source. The clear cutting method is one exception where artificial planting, vegetative regeneration or seeding is necessary when the cut area limits complete reproductive tree seeding.
Methods to use when even age management is preferred:
The Clearcutting Method - When cutting all trees and removing the entire stand that lays bare the ground, you have a clearcut. A clearing of all trees should be considered when residual trees are starting to lose economic value, when biologic over maturity leads to decadent stands, when the purity of a stand is compromised by cull and lower value trees, when the coppice method of regeneration is used (see below) or when disease and insect invasions threaten the loss of a stand.
Clearcuts can be regenerated either by natural or by artificial means. To use a natural regeneration method means you must have an available seed source of a desired species in the area and a site/soil condition advantageous to seed germination. If and when these natural conditions are not available, artificial regeneration via nursery seedling plantings or prepared seed dispersal must be used.
The Seed-tree Method - This method is simply what it suggests. Upon removing most of the mature timber, a small number of "seed trees" are left singly or in small groups to establish the next even-aged forest. In effect, you are not dependent on trees outside the cutting area but must be concerned about the trees you do leave as the seed source. The "leave" trees should be healthy and able to survive high winds, produce viable seeds prolifically and enough trees should be left to do the job.
The Shelterwood Method - A shelterwood condition is left when a stand has had a series of cuttings over the period between establishment and harvest, often called the "rotation period". These harvests and thinnings occur over a relatively short portion of the rotation by which the establishment of even-aged reproduction is encouraged under a partial shelter of seed trees.
There are two objectives of a shelterwood cut - making ground space available by cutting trees of lowering value and using trees increasing in value as a seed source and for seedling protection as these trees continue to financially mature. You are maintaining the best trees to grow while cutting trees with lower value for new understory seedling space. Obviously, this is not a good method where there will be only intolerant (light-loving tree species) tree seeds available to regenerate.
The sequence of this particular method should be ordered by: first making a preparatory cutting which prepares and stimulates seed trees for reproduction; then a seed tree cutting to further open vacant growing space for seeding; then a removal cutting which frees the established seedlings.
Methods to use when uneven-aged management is preferred:
The Selection Method - The selection harvest method is the removal of mature timber, usually the oldest or largest trees, either as single scattered individuals or in small groups. Under this concept, the removal of these trees should never allow a stand to revert back to an even-age. Theoretically, this style of cutting can be repeated indefinitely with adequate wood harvest volumes.
This selection method has the widest variety of interpretations of any cutting method. Many conflicting objectives (timber management, watershed and wildlife enhancement, recreation) must be considered and managed differently under this scheme. Foresters know they are getting it right when at least three well defined age classes are maintained. Age classes are groups of similar aged trees ranging from sapling sized trees to intermediate sized trees to trees approaching harvest.
The Coppice-forest or Sprout Method:
The coppice method produces tree stands that originate mostly from vegetative regeneration. It can also be described as low forest regeneration in the form of sprouts or layered branches as opposed to the above examples of high forest seed regeneration. Many hardwood tree species and only a very few coniferous trees have the ability to sprout from roots and stumps. This method is limited to these woody plant types.Sprouting tree species respond immediately when cut and sprout with exceptional vigor and growth. They outpace seedling growth by far, especially when cutting is made during the dormant period but may suffer from frost damage if cut during the late growing season. A clear cut is often the best cutting method.