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Silviculture

Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests to meet diverse needs and values.

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Silviculture is the application of the principles of forest ecology to a stand of trees to help meet specified objectives.

Objectives can include income, wildlife habitat, water quality, recreation, or any other values a forest is capable of providing.

Silviculture also has to do with sustained yield and keeping the forest productive through multiple rotations (lifespans of trees) for wildlife habitats, clean water and recreational uses as well as forest products.

To understand silviculture, one must first understand silvics. Silvics involves understanding how trees grow, reproduce, and respond to environmental changes.

Some tree species thrive in shade. These species can live, grow, and reproduce in shade and semi shade conditions. Many tree species prefer or require full sunlight. These species require full sunlight to reproduce, after which they grow best in full sunlight or as part of the over story 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, elm, and birch are intermediate in their sunlight requirements.

Species are generally divided into tolerant, intolerant, and intermediate categories.

Intolerant Species

Intolerant species are generally the “first in” after an event such as a clear-cut or a major fire that substantially opens the canopy.

These trees are often called pioneer species.

These trees tend to:

- be fast growing

- be short-lived

- have light seeds

Tolerant Species

These trees normally are not the first to colonize open areas.  Instead, they grow up into an existing canopy.

Usually, these trees are found in the “climax community.”

These trees tend to:

- live a long time

- grow slowly

- have heavier seeds

Intermediate Species

As the name implies, these trees have characteristics that are “in between” the tolerants and the intolerants.

Silvicultural regeneration methods combine both the harvest of the timber on the stand and re-establishment of the forest. The proper practice of sustainable forestry  should mitigate the potential negative impacts, but all harvest methods will have some impacts on the land and residual stand.  The practice of sustainable forestry limits the impacts such that the values of the forest are maintained in perpetuity. Following are some common methods:

Single-tree selection – The single-tree selection method is an uneven-aged regeneration method most suitable when shade tolerant species regeneration is desired. It is typical for older and diseased trees to be removed, thus thinning the stand and allowing for younger, healthy trees to grow. Single-tree selection can be very difficult to implement in dense or sensitive stands and residual stand damage can occur.

Group selection – The group selection method is an uneven-aged regeneration method that can be used when mid-tolerant species regeneration is desired. The group selection method can still result in residual stand damage in dense stands, however directional falling can minimize the damage. Additionally, foresters can select across the range of diameter classes in the stand and maintain a mosaic of age and diameter classes.

Clear-cut – An even-aged regeneration method that can employ either natural or artificial regeneration. Clear-cutting can be biologically appropriate with species that typically regenerate from stand replacing fires or other major disturbances, such as lodge pole pine (Pinus contorta). Alternatively, clear-cutting can change the dominating species on a stand with the introduction of non-native and invasive species as was shown at the Blodgett Experimental Forest near Georgetown California. Additionally, clear-cutting can prolong slash decomposition, expose soil to erosion, impact visual appeal of a landscape and remove essential wildlife habitat. It is particularly useful in regeneration of tree species such as Douglas-fir (Pseudotsuga menziesii) which is shade intolerant.

Seed-tree – An even-aged regeneration method that retains widely spaced residual trees in order to provide uniform seed dispersal across a harvested area. In the seed-tree method, 2-12 seed trees per acre (5-30/ha) are left standing in order to regenerate the forest. They will be retained until regeneration has become established at which point they may be removed. It may not always be economically viable or biologically desirable to re-enter the stand to remove the remaining seed trees. Seed-tree cuts can also be viewed as a clear-cut with natural regeneration and can also have all of the problems associated with clear-cutting. This method is most suited for light-seeded species and those not prone to wind throw.

Shelterwood - A regeneration method that removes trees in a series of three harvests: 1) Preparatory cut; 2) Establishment cut; and 3) Removal cut. The method’s objective is to establish new forest reproduction under the shelter of the retained trees. Unlike the seed-tree method, residual trees alter understory environmental conditions (i.e. sunlight, temperature, and moisture) that influence tree seedling growth.

Coppicing – A regeneration method which depends on the sprouting of cut trees. Most hardwoods, the coast redwood, and certain pines naturally sprout from stumps and can be managed through coppicing. Coppicing is generally used to produce fuel wood, pulpwood, and other products dependent on small trees. In Compound coppicing or coppicing with standards, some trees of the highest quality trees are retained for multiple rotations in order to obtain larger trees for different purposes. A close relative of coppicing is pollarding.