Silvicultural Systems in British Columbia

Clearcutting, seed tree, shelterwood, and selection


Silviculture
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During the pioneering years of settlement in British Columbia, timber harvesting was one of the primary means of economic development. Our forests were considered limitless, and there was little consideration or knowledge of forest resources other than timber.

Over time, the social values placed on our forests have changed. Non-timber forest resources, such as fish and wildlife, water quality, recreational opportunities, and visual aesthetics, are now recognized and highly valued by the public. At the same time, forest managers are learning more about the complexities of forest ecosystems.

In response to these new developments, forest practices are changing across the province. This, in turn, has stimulated an increasing interest in a wide range of silvicultural systems, particularly those involving partial cutting.


What is a Silvicultural system?

A silvicultural system is a cycle of activities by which a forest stand, or group of trees, is harvested, regenerated, and tended over time. These activities include: Four general types of silvicultural systems are used in British Columbia. The names of these silvicultural systems reflect the type of forest structure remaining after the initial harvest. They are normally referred to as: All of these systems can be modified to accommodate local site conditions and management objectives.

There are two basic classes of silvicultural systems: even-aged and uneven-aged. Even-aged systems generally create stands where the trees are approximately the same age, or one age class. However, in some cases, even-aged systems can result in two distinct age classes of trees when some older trees are left behind after harvesting.

Clearcutting, seed tree, and shelterwood are generally considered to be even-aged silvicultural systems.

With uneven-aged systems, such as selection, stands are maintained or created where the trees are of several distinct age classes.

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An historical perspective of silvicultural systems in British Columbia

Clearcutting has traditionally been the primary method of timber harvesting in British Columbia. This predominance can be attributed to economics, terrain, available harvesting technology, and treespecies ecology.

On the coast, clearcutting has been preferred because it is an economical and safe means of harvesting large trees on steep slopes. In addition, the regeneration of most coastal tree species is ecologically suited to the open conditions created by clearcutting.

Clearcutting has also been used extensively in other parts of the province. However, in the Interior, a wider variety of silvicultural systems have been used. The Interior's climate, terrain, and tree species are generally better suited to partial-cutting systems.

Early attempts at partial cutting often led to what is called high grading. With high grading, only the trees of highest quality and value were harvested, leaving behind poor-quality trees and less desirable species to regenerate the new forest stand. The consequences of high grading were soon realized and the practice was disallowed. Today, partial- cutting systems are based on sound ecological principles to avoid repeating the mistakes of the past.

In 1990, the Forest Service initiated a provincewide research and development program to conduct further investigations into modified clearcutting and partial-cutting systems. This program is designed to increase our understanding and experience in applying these different systems, and identify areas in the province where their use can be expanded.

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Choosing a silvicultural system

There are many factors to consider when selecting a silvicultural system. Each system has advantages and disadvantages which make it appropriate for use on some sites, but not on others. Some important factors to consider are:

Silviculture Factors
Factors to consider when choosing an appropriate
silviculture system

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The four silvicultural systems used in British Columbia

The clearcutting system

With the clearcutting silvicultural system, trees within a cut block are removed in a single harvest. This ends one growth phase and begins another.

Clearcutting is the standard form of harvesting for species such as lodgepole pine and coastal Douglas fir, which are generally intolerant of shade and regenerate poorly under the canopy of mature trees.

Clearcutting system
Clearcutting ends the growth cycle of a mature forest stand and begins the regeneration of a new, even-aged stand: soon after harvest, 5-7 years after harvest, 15-20 years after harvest

With clearcutting, regeneration is achieved either naturally or by planting. Sources of natural regeneration include seed on the forest floor, seed from adjacent trees, or young trees that established themselves prior to harvesting.

Some advantages of the clearcutting system:

Some disadvantagess of the clearcutting system:

The seed-tree system

Seed tree system
With the seed-tree system, the largest, most desirable trees are generally left behind to help regenerate a new stand

The seed-tree silvicultural system leaves selected trees standing in a cut block, either individually or in small groups, to provide a natural seed source for regeneration. As the largest, most desirable trees tend to be the most wind resistant and will produce high-quality trees for the next generation, they are generally left as seed trees.

The number and distribution of seed trees depends on many factors, such as the preferred density of seedlings, how frequently the seed trees produce cones, and the distance seed travels from parent trees. Seed trees are generally harvested once regeneration has been established. However, they may be retained where they are important to wildlife, biological diversity, visual quality, or where removal would damage the new forest stand.

Some advantages of the seed-tree system:

Some disadvantages of the seed-tree system:

The shelterwood system

Shelterwood system
With the shelterwood system, the arrangement of mature trees left after each succesive cut depends on management objectives and local site conditions

With the shelterwood silvicultural system, mature trees are removed in a series of cuts designed to establish a new, even-aged stand under the shelter of the remaining trees. These mature trees provide protection and shelter to developing trees, which may be established either naturally or by planting.

Some advantages of the shelterwood system:

Some disadvantages of the shelterwood system:

The selection system

Selection system 1
With the selection system, trees may be harvested individually or in small groups up to several tree lengths in width

The selection silvicultural system maintains a continuous, uneven-aged forest cover by harvesting a limited number of trees, of various sizes and ages, over time. Mature and immature trees are harvested either individually (single-tree selection) or in groups (group selection), and harvests take place over regular intervals of 15 to 30 years. While the single- tree selection system is aesthetically pleasing, it is often costly and difficult to apply to most of the province's ecosystems and tree species.

The selection system promotes continuous regeneration by creating gaps in the forest through the removal of selected trees. To ensure regenerated areas remain healthy and grow quickly, the new trees should be thinned and tended.

Some advantages of the selection system:

Some disadvantages of the selection system:

Selection system 2
With group selection, small areas of even-aged regeneration are created

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Modifying silvicultural systems to meet British Columbia's needs

British Columbia is an ecologically diverse province, containing more than 600 identified ecosystems. Few forestry regions in the world have as much variation and complexity in their forests.

Biological Diversity
With any silvilculture system, trees may be reserved for wildlife habitat and biological diversity, as shown in this clearcut

As a result, the four silvicultural systems used in British Columbia are often modified to accommodate local site conditions. For example, clearcutting with reserves retains groups of trees within a cut block to maintain important values such as wildlife habitat and biological diversity.

Another important modification to the way silvicultural systems are applied in British Columbia involves the use of forest ecosystem networks (FENs). These networks consist of special management areas, such as old growth, riparian zones, or critical wildlife habitat, that are connected by forested corridors. FENs are used in conjunction with various silvicultural systems to maintain a portion of the forest landscape in a natural state.

The application of silvicultural systems in British Columbia will continue to evolve as we learn more about forest ecosystems and gain experience with those systems that involve partial cutting. By carefully choosing the most appropriate silvicultural system and modifying it to accommodate local site conditions and management objectives, the environmental impacts of timber harvesting can be kept to a minimum. B.C.'s Forest Practices Code is designed to address some of these issues.

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For more information

For more information on silvicultural systems, please contact your nearest Forest Service office or:

Forest Practices Branch,
P.O. Box 9513 Stn. Prov. Gov.
Victoria, British Columbia,
V8W 9C2

Contact Tim Ebata tim.ebata@gems8.gov.bc.ca. if you have comments on the presentation of this information.

Silviculture systems