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Fire

2.1 Making the Decision to Burn

2.2 Setting Burn Objectives that will Achieve Silviculture Objectives

2.3 Developing the Burn Prescription

2.4 Conducting the Burn

2.5 Post-fire Impact Assessments

2 Planning for Prescribed Burning

Good burning starts with good planning. Basic objectives for prescribed burning include reducing the risk of wildfire and preparing the site for reforestation while preserving the potential of the site to grow trees and minimizing detrimental effects on the environment.

2.1 Making the Decision to Burn

The decision to burn is usually based on a pre-harvest silviculture assessment and prescription. Site classification and soil properties for each site series are determined during data collection for the Pre-harvest Silviculture Prescription (PHSP) (see the chapter, "Pre-harvest Silviculture Prescriptions" for more information). The basic site characteristics are used to identify site limiting factors that may be ameliorated by site preparation. If site preparation is required, the forest manager must weigh the strengths and weaknesses of the available site preparation options to determine which alternative can best meet the required treatment objectives. The use of prescribed fire is to be limited to those sites where it is the most ecologically suitable site treatment for achieving the desired objectives of land and resource management prescriptions. If prescribed fire is seen as the most suitable treatment, it will be noted as such on the PHSP.

After harvesting is complete, a follow-up assessment should be undertaken to ensure that the treatment proposed in the PHSP is feasible and acceptable. The FS 117 Site Preparation Guide (see Appendix 1, Forms Management) provides a mechanism for validating the site preparation option indicated on the PHSP and provides an opportunity to state treatment objectives more explicitly. Burn objectives are expressed in terms of slash fuel reduction, organic layer reduction, and mineral soil exposure.

2.2 Setting Burn Objectives that will Achieve Silviculture Objectives

The Prescribed Fire Predictor (PFP) (Muraro 1975) assigns an impact rank to each fire ranging from 1 (lowest) to 8 (highest). For each impact rank, the predictor indicates the effect on percent reduction of duff, percent exposure of mineral soil, and percent reduction of slash fuels.

Translating silvicultural objectives into burn objectives is often difficult because information on the correlation between fire impacts and specific silvicultural objectives, such as increasing soil temperature or achieving a desired level of vegetation control, are often poorly defined or are stated in very general terms. At present, ecosystem guides are being prepared for some biogeoclimatic subzones (e.g.,Trowbridge et al. 1989). However, there is no substitute for local experience on similar ecosystems.

For more detailed information on setting burn objectives, see Trowbridge et al. [1989], Hawkes et al. [1990], and Haeussler [1991]. A computer system SYTEPREP has also been developed for use in the Nelson Forest Region. This system indicates how fire severity will affect vegetation regrowth and site limiting factors.

2.3 Developing the Burn Prescription

To achieve with certainty the burn objectives you have chosen, it is important to develop a prescribed fire prescription. The burn prescription should consider site sensitivity, the quantity, arrangement and condition of the fuel, fuel moisture requirements, weather, ignition pattern, the risk of escape, and smoke management (see "Smoke Management" in "1.5, Prescribed Fire and Air Quality," this section). The prescription must state the desired level of fuel and forest floor consumption, and when applicable, the maximum reduction in forest floor depth allowed to ensure that site and soil productivity are not degraded. The Prescribed Fire Predictor is the principal aid used in British Columbia to translate burning objectives into a prescribed fire prescription. For further information on use of this tool, see Lawson [1981].

When making the burn prescription, the forest manager must not focus on a single objective at the exclusion of other site factors (i.e., a very high impact burn might be desirable for vegetation control but may be unacceptable due to site sensitivity). Similarly, a high impact fall burn might be ideal for reducing the forest floor but might be unacceptable in terms of smoke management.

Three Forest Service forms, the FS 117, the FS 117A and the FS 117B (see Appendix 1, Forms Management), play a guiding role in developing the burn prescription. The FS 117 is used at the prescription phase to aid in comparing a prescribed burn to other alternatives and to determine the feasibility of a burn to meet stated silvicultural objectives. The FS 117A is completed in three stages. Prior to the burn, parameters such as desired impact and burning conditions required to meet desired objectives are stated. At the time of the burn, weather conditions and daily predictor readings are recorded. After burning is complete, impact is evaluated.

A Prescribed Burning Plan, the FS 117B, must be prepared prior to conducting a burn. This form details specific burn information such as work required to prepare the site for burning, ignition plan, control, mop up, and the resources required in the event of an escape. Burning must be carried out under the authority of the Burning Permit and the plan must be identified on the permit.

For details on administration associated with the burning permit see the Protection Manual, Volume 1, Chapter 3, Burning Permits.

Once the prescription is complete, determine how many days in an average year, and in what months the fire weather values are likely to occur for the nearest network weather station, using the Protection Information System function - Weather Prescription (WPX). If, during the test, the prescription fails to achieve stated objectives, revise the prescription accordingly.

For further information on the burn prescription, consult Hawkes et al. [1990], the Ministry of Forests Protection Manual, Chapter 4, and the Forests Protection Operational Fire Systems Manual.

2.4 Conducting the Burn

The prescribed burn must be conducted in accordance with the Prescribed Burning Plan and Burning Permit. Safety of the public, structures and standing timber must receive the highest priority.

In broadcast burning, advantage should be taken of natural fire breaks, and fireguards should be constructed as necessary to protect leave strips, patches of acceptable advance regeneration and young germinants. Fire must be kept away from the margins of lakes, major water courses and standing timber.

For additional information regarding ignition systems, patterns of ignition, and monitoring of the burn, see Ministry of Forests Protection Manual, Chapter 4, Hawkes et al. [1990] and Walstad et al. [1990].

2.5 Post-fire Impact Assessments

Post-fire impact assessments on site and soil conditions shall be conducted as soon as practical following all prescribed burning. Silviculture Regulation 6 (b.1) (c) states,

"where site preparation is required by an approved prescription, to carry out a silviculture survey, not later than 60 days after completion of the site preparation unless it is physically impossible to carry out the survey in which case it shall be carried out as soon as it becomes possible, and keep a written report of the survey capable of enabling a district manager to determine whether the site preparation is likely to enable achievement of the stocking standards in compliance with the approved prescription."

Slash and forest floor consumption and mineral soil exposure are recorded using visual estimates on the Site Preparation Report (FS 737). For more accurate site-specific estimates of slash consumption and forest floor depth of burn, see procedures outlined in Trowbridge et al. [1987].


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Copyright 1999 Province of British Columbia
Forest Practices Branch
BC Ministry of Forests
This page was last updated December 1993

Comments to: Tim Ebata <Tim.Ebata@gems8.gov.bc.ca>