Silviculture: An Overview

Silviculture is the science and art of growing and tending forest crops. More particularly, the term silviculture means the theory and practice of controlling the establishment, composition, character, and growth of forest stands to satisfy specific objectives (Broun 1912, Kostler 1956, Helms 1998, Daniel and others 1979, Smith 1986). The principal focus of silviculture, particularly in managing upland central hardwoods, has been timber production (Mills and others 1987). However, silviculture also involves the manipulation of forest stands to achieve a variety of benefits other than timber. These benefits are defined by forest owners and may include aesthetics, wildlife habitat, watershed protection, or recreation, to name a few. Silviculture, then, is used to provide an effective and appropriate means for managing a stand to provide desired benefits, whatever they may be, and to sustain them in perpetuity (Nyland 1996).

To serve these purposes, silviculturists draw upon principles and theory amassed through scientific inquiry in botany, zoology, soil science, physical sciences, ecology, silvics, managerial science, economics, and quantitative methods. All contribute techniques and information that foresters can use in identifying and evaluating the options for practical management, and in forecasting the likely outcomes from a given set of silvicultural treatments. In both theory and practice, silviculture draws heavily upon silvics. By definition, silvics deals with principles underlying the growth and development of single trees and of the forest as a biological unit.

Silvicultural systems provide the conceptual framework for forest management by describing the long-term plan for managing an individual stand to sustain a particular set of values (see figure; Champion and Trevor 1938, Helms 1998, Van Lear 1981, Smith 1986). The three main functions of a silvicultural system are (1) regeneration, (2) tending, and (3) harvesting.

Cycle of an Even-Aged Silvicultural System

Silviculturists generally classify silvicultural systems into two broad groups: "high-forest" methods that rely on reproduction from seed and "low-forest" or coppice methods that rely on sprout reproduction (Smith 1986). Within high-forest methods, there are three subdivisions: even-age systems, uneven-age systems, and two-age systems. Even-age systems use regeneration harvest methods that create even-aged stands. By convention, the spread of ages in an even-aged stand does not differ by more than 20 percent of the intended rotation. Even-age methods include clearcuttting, shelterwood, and seed-tree methods. Uneven-age systems use regeneration harvest methods that create uneven-aged stands. Commonly at least three distinct age classes are required for an uneven-aged stand. Uneven-age methods include single-tree selection and group selection methods. Two-age systems provide for regeneration of shade-intolerant species while carrying a variable density overstory of mature trees.

Additional site preparation treatments may be a necessary component of a silvicultural system. Site preparation includes any treatment that modifies existing vegetative or physical site conditions to improve seed germination and survival or subsequent growth of desired seedlings. Active site preparation can be accomplished by prescribed burning, mechanical, or chemical methods (herbicides).

The other major component of a silvicultural system is the tending of developing or mature forest stands; its techniques that collectively called intermediate management. Although intermediate management can involve practices that improve the site (fertilization, etc.) or manage pests (pesticides, etc.), it often involves intermediate cuttings. The several types of intermediate cuttings are distinguished by the stage of stand development during which cuttings are made and by the criteria used for targeting tree removal. Thinnings are intermediate cuttings made in immature stands to control stand density. Release operations are intermediate treatments designed to free young stands from undesirable vegetation that threatens to suppress them. Improvement, sanitation, and salvage cuttings are intermediate treatments aimed at removing poor quality, diseased, or dead and dying trees. In addition to the above treatments, which tend to focus on the condition of the stand, crop-tree management is a type of intermediate management that focuses on individual trees of potentially high value to the landowner.

Different forest ecosystems managed for different goals will usually require different silvicultural systems. Silvicultural systems consist of a planned program of silvicultural treatments during the whole life of the stand; silvicultural systems include not only reproduction cuttings but also any tending operations or intermediate cuttings (Nyland 1996).  A comparative analysis of silvicultural systems appropriate for southern Appalachian ecosystem management reveals several interesting findings. 

See: Adaptive silviculture