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Silviculture

The key to effective forest management planning is determining a silvicultural system. A silvicultural system is the collection of treatments to be applied over the life of a stand. These systems are typically described by the method of harvest and regeneration employed.

In general these systems are:

 

  • Clearcutting: The entire stand is cut at one time and naturally or artificially regenerate

[graphic] Illustration of clearcutting.

  • Seed-tree: Like clearcutting, but with some larger or mature trees left to provide seed for establishing a new stand. Seed trees may be removed at a later date.

[graphic] Illustration of seed trees

  • Shelterwood: Partial harvesting that allows new stems to grow up under an overstory of maturing trees. The shelterwood may be removed at a later date (e.g., 5 to 10 years)

[graphic] Illustration of shelterwood

  • Selection: Individual or groups of trees are harvested to make space for natural regeneration.

[graphic] Illustration of single tree selection

Single Tree Selection

[graphic] Illustration of group tree selection

Group Tree Selection

Clearcutting, seed-tree, and shelterwood systems produce forests of primarily one age class (assuming seed trees and shelterwood trees are eventually removed) and are commonly referred to as even-aged management. Selection systems produce forests of several to many age classes and are commonly referred to as uneven-aged management. However, in reality, the entire silvicultural system may be more complicated and involve a number of silvicultural treatments such as site preparation, weeding and cleaning, pre-commercial thinning, commercial thinning, pruning, etc.

[graphic] Illustration of uneven-aged, Two-aged, and Even-aged stand types

Figure 1. Types of stand age structure (Definitions from: Helms, John A. 1998. Dictionary of Forestry.)

Importantly, the feasibility and appropriateness of a silvicultural system depends on your objectives, existing stand conditions, the characteristics of the individual tree species involved, and your willingness and ability to make these investments. Pioneer or light-demanding species respond well to high levels of light and thus clearcutting is an effective harvest and regeneration strategy. Such species typically do not grow well in the shade. Conversely, late successional and less light-demanding species will often grow best under shelterwood or selection systems. But there are complicating forest health, cost, habitat, and aesthetic issues that hinder broad generalizations. The individual species and cover type guidelines described are intended to deal with these issues in detail.

Stand development

In application, silvicultural treatments can lead to a change in age class structure for the new or remaining forest. Clear-cutting and shelterwood systems typically lead to an even-aged structure. Selective cutting typically leads to an uneven-age structure. Using seed trees can lead to an even-age structure for the new stand if regeneration occurs quickly; if regeneration occurs gradually, the result can be an uneven aged stand. Also, if the seed trees are left on the area for a long time period, the new stand will have two to a many age class structure. Clearly, specifying the silvicultural system for a particular stand is an important step. Even-aged management is perhaps the simplest approach in many respects, even though it constitutes a major disturbance of the site. Conversely, uneven-aged management is outwardly appealing because it leaves the site in a continuous green state. However, uneven-aged management often requires more expertise and thought in specifying choices among treatments. For either choice of age class structure, failure to consider choices carefully can lead to forest health problems and reduced productivity. In examples, we try to describe both the advantages and disadvantages of approaches.

 

 
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North Central Region Forest Management Guide: A cooperative project of the USDA Forest Service and University of Minnesota.
USDA Forest Service - Northern Research Station
Last Modified:  05/25/2006