Using Prescribed Fire for Silvicultural Objectives

Silviculture is the theory and practice of controlling the establishment, composition, character, and growth of forest stands to satisfy specific objectives. It is an applied science that rests on the more fundamental natural and social sciences. The immediate foundation of silviculture in the natural sciences is silvics, which deals with the growth and development of single trees and other biota as well as whole forest ecosystems. Before any silvicultural prescription is applied, there must be a thorough knowledge of the silvics of the tree species and the silvicultural systems that can be implemented. This is especially true when prescribed fire is going to be part of any management plan. In addition to knowledge of the silvics of a species, when using prescribed fire it is necessary to know the fire effects on that species. With this knowledge, managers can plan prescribed fires so that their intensity and size are no greater than necessary to achieve some clearly defined purpose of timber production, reduction of fire hazard, wildlife management, restoration, or improving grazing opportunities.  The fact that a species is adapted to fire does not necessarily mean that fire has a practical, safe, and feasible place in its silviculture. Other types of disturbances/activities can be used to simulate the effects of fire; among them are mechanical treatments, various cutting practices, and herbicide application. 

There are widely used syntheses currently available on the topics of silvics, silvicultural systems, and fire effects:

• Silvics of North America (Burns and Honkala 1990) provides information on tree species habitat (range, climate, soils, topography, associations), life history (reproduction and early growth, sapling and pole stages to maturity); special uses; and genetics.
• Silvicultural Systems for the Major Forest Types of the United States (Burns 1983) provides information on how different silvicultural systems are used to manage various tree species.
• Fire Effects Information System is an extensive on-line database that summarizes and synthesizes research about fire ecology, fire effects, and fire management considerations for various plant and animal species in the U.S.

The following sections, summarized from the above references and others, organize information on how prescribed fire can be used in the silviculture of pines and hardwoods:

General silvicultural uses of prescribed fire

The above links provide information on how prescribed fire can be used for the management of specific timber species.  The following links provide more general information on the uses of prescribed fire for other forest management objectives.  Some of these uses are also applicable in non-forested systems and therefore are not exclusively silvicultural objectives.

• Hazardous fuel reduction: The most common objective of prescribed burning is fuel reduction. The effect in fuel reduction is to interrupt the horizontal and sometimes the vertical continuity of flammable materials. It must be remembered that prescribed burning does not render any area fireproof, except temporarily. It is not a substitute for a well-developed system of fire control.
• Seedbed/site preparation: Prescribed burning can be very effective in seedbed preparation for regenerating wind-disseminated species, like pines, which become established most readily on bare mineral soil. In additional, it is beneficial in hampering reproduction of heavy-seeded species (maple and beech) that are prone to stem-girdling from fire after establishment. It is these species that would displace many of the pines in the course of natural succession.
• Logging debris disposal: Following logging, logging debris can pose a fuel hazard and impede preparing the site for seeding or planting.  Prescribed burns can be used to reduce the amount of logging debris, however, special care should be taken to prevent smoldering fires and/or damage to soil.
• Manage competing vegetation: Prescribed burning is a means of controlling competing vegetation. This has the effect of slowing/stopping natural succession by killing understory species which would otherwise dominate the forest stand. When the goal is to prevent invasion by hardwoods, as in stands of southern pines, burning must be done fairly often because only the seedlings will be killed. The saplings have enough of a developed root-system to re-sprout and larger trees may only be scarred. If the goal is to kill perennial grasses, this will only happen when a fire burns long enough to heat the soil to the depth where the roots are growing. Both in nature and practice, fires must occur quite frequently if understory vegetation and brush are to be kept in check.
• Range and Wildlife management : The use of prescribed burning for the improvement of grazing for livestock is probably the reason for the earliest use of fire in forests. This role has expanded for improving wildlife habitat as fire stimulates the production of herbaceous species and sprouting of woody plants.
• Insect and disease control: Prescribed burning can be very effective for control of pests, though it can increase the problems caused by some if used improperly. One of the major uses of prescribed burning for pests in southern pine forests is its direct control of brown-spot fungus in grass-stage longleaf pine seedlings. There have also been some indications that prescribed burning may reduce problems with annosus root rot.
• Recreation management (Enhancing appearance and Improving access): Prescribed burning is employed in recreation management to maintain park-like appearances that were common prior to settlement of the Southeast and the subsequent reduction in area burned by wildfires. Large areas of southern pine forests now have an understory of shrubs, small trees and briars. 
   

Planning and conducting prescribed burns

The type of prescribed fire used to carry out a silvicultural practice is based on the reason for burning. When you have determined your objectives, then you need to consider weather and fuel conditions and what firing technique to use. These guidelines, found in A Guide for Prescribed Fire in Southern Forests (USDA Forest Service 1989), are also available in the following sections of the Encyclopedia of Southern Fire Science:

• Weather and fuel conditions
• Firing techniques