Prescribed fire is the application of fire to a specific land area to accomplish pre-determined forest management, or other land management objectives. It may also include a fire that is started by lightning and is managed to accomplish specific, ecosystem-based, management objectives according to a previously specified set of burning conditions, while protecting socio-economic values at risk.
Prescribed fire has a number of applications in Ontario and is used to:
- Lessen fire hazard by reducing the amount of fuels on the ground
- Clear forest areas of woody debris to prepare seed beds and planting sites
- Remove undesirable plants that compete for nutrients with desirable species
- Develop and enhance wildlife habitat
- Allow fire as a natural process to manage, maintain and enhance ecosystems
- Conduct research on fire's effects
- Control insect pests and diseases
- Remove undergrowth to allow sunlight to reach the forest floor, encouraging the growth of selected species
- Release bound up nutrients in woody material, in the form of ash, making them more readily available to the ecosystem and for enhanced plant growth
In addition to protecting people and values, today's fire management program uses the beneficial effects of fire to help achieve diverse resource management objectives on the landscape. Fire is used to reduce and eliminate hazards, to prepare an area for reforestation and to renew ecosystems and habitat. For certain applications, a prescribed fire can help achieve more than one objective. For example, a fire set to remove the hazard posed by spruce budworm-killed balsam fire could provide the added benefit of forest renewal through the re-introduction of fire adaptive species.
Natural disturbances such as insect infestations, tree diseases and strong wind storms can result in large areas of dead, unhealthy or blow down forest. Trees that die, quickly dry out and become a wildfire hazard. Lightning strikes remain the main source of ignition in Ontario's forests. Fires that occur in dead or dying forests often grow rapidly and become very difficult and costly to extinguish. Resource managers may prescribe that portions of an affected forest be ignited to provide fuel breaks and to eliminate the hazardous areas through burning. If the area affected is relatively small or close to property values, the prescribed fire may be designed to consume all of the dead or dying trees.
Prescribed burning is used to prepare harvested forest lands for planting or seeding of the next forest. The fire is set within a range of fuel and weather conditions that are calculated to remove the target levels of debris, competing vegetation and duff layer ground cover. Outside this range, the fire may not burn enough material, or be so intense that soil is damaged, nutrients are destroyed and no protective, organic litter layer is left. The fire exposes mineral soil and new sites on the forest floor that are receptive to plantings and tree seed. Ash from the fire releases nutrients that have been stored in the vegetation, this assists the growth of the new forest. With most of the logging debris removed, tree planters can properly space the plantings to ensure their establishment and growth.
Ecosystem and Habitat Renewal
In the absence of wildfire, ecosystems change over time, often becoming less productive and hosting a diminishing variety of flora and fauna. On a landscape level, fire is an important mechanism in the maintenance of wildlife diversity by creating younger, early successional habitats that contain a range of preferred and nutritious plant foods. Prescribed fire is used by resource managers to renew and sustain ecosystems and maintain wildlife habitat on a local scale.
Low intensity prescribed burning applied to the understorey of mature white and red pine stands aids in the successful regeneration of these old growth species. Fire releases seed from cones, reduces the ground litter layer, increases nutrient flow, eliminates parasites and diseases and reduces competition for the seedlings that will emerge. In most instances, fire does not damage the mature trees in the overstorey that are armoured with a thick bark.
Prescribed burning may also be used on grass and shrubland areas to prevent the growth of trees spread by seed from the adjacent forest. Periodic burning maintains and renews the areas in the forest mosaic. Wildlife species that require the specific mix of habitat conditions offered by the grassland-forest complex, including the edge between them, stay in the area.
Many prescribed burns in Ontario are carried out as part of the forest management process. After timber companies harvest a forest, the site is often littered with logging debris called slash. Slash consists of branches, tree tops, dead trees and brush. This makes it difficult for tree planters to move through an area to plant new trees. Depending upon the amount of slash present, it can also make a site unsuitable for other methods of regeneration. Prescribed burning removes this logging debris. It also reduces the duff (humus) layer or exposes underlying mineral soil on some sites, making it easier for certain species to grow.
Resource managers assess forest areas to determine if they require site preparation before regeneration. If a site does require preparation, the method selected will either be mechanical, chemical, prescribed fire or a combination of these methods. The method chosen will depend on the amount of debris present, the terrain, and the proposed method of regeneration. For jack pine sites, it is desirable to remove as much of the duff layer as possible to expose mineral soil. Spruce sites require little or no duff removal. Undesirable vegetation, which would initially compete with the newly planted trees during their first year of growth, can also be removed.
Any prescribed burn conducted in Ontario requires a Prescribed Burn Plan, this is a detailed document outlining the steps required to safely conduct a burn and successfully meet the resource management objectives. It is developed by fire and resource managers working together as a team. Each team member is responsible for various aspects of the burn. The team considers a number of key elements.
Natural boundaries on the perimeter of the proposed burn site are taken into account. These consist of lakes, rivers, swamps, stands of deciduous trees and roads. Each may act as a barrier to help stop the prescribed burn from traveling beyond predetermined limits.
Nearby values are considered and protection strategies developed. Values can include buildings, stands of timber suitable for harvesting, endangered wildlife species (such as eagles), cut woods, plantations, etc.
The amount, size and type of forest fuels on the site and their moisture condition determines the intensity of the burn. If these fuels are to wet, they won't burn well, if they are to dry, they may burn too intensely.
Weather is the single final determining factor on when a burn takes place. The weather leading up to the day of the burn is closely monitored. If it has rained extensively, the burn will be postponed. Similarly, the burn may be postponed if it has been very hot and dry, or if it is too windy on the scheduled day of the burn. During the burn, weather conditions such as humidity, temperature and wind are closely monitored.
Once all planning conditions have been met, the Prescribed Burn Fire Boss gives the approval to proceed with ignition. This can be carried out either by ground or aerial devices, or a combination of both. Once ignited, the fire should pass cleanly over the site, burning off slash fuels or vegetation and the desired amount of duff and/or exposing the desired amount of mineral soil.
After burning has been completed, fire crews patrol the edge of the fire extinguishing all 'hot spots', or small pockets of fire. This ensures that warm weather or winds on the days following do not re-kindle the prescribed burn and turn it into a wildfire.
Prescribed burning is, and will continue to be, a viable resource management tool used to ensure the continued growth and health of forests in Ontario.