Urban Forestry Projects

Prescribed Burn

Urban Forestry Prescribed Burn Program

Prescribed burn at high park

A prescribed burn is a deliberately set and carefully controlled fire that burns low to the ground and consumes dried leaves, small twigs and grass stems but does not harm larger trees. The City of Toronto uses prescribed burns as one management tool in the restoration and maintenance of a variety of oak woodland, prairie, and savannah habitats. Prescribed burning can have many benefits including:

  • encouragement of native savannah grasses, shrubs and wildflower plantings,
  • encouragement of oak regeneration,
  • stimulating renewal and new growth, and increased seed production of native plants existing black oak savannah habitats,
  • setting back growth of undesirable invasive species.

Frequently Asked Questions

ExpandWhat is a prescribed burn?

A prescribed burn is a deliberately set and carefully controlled fire that burns low to the ground and consumes dried leaves, small twigs and grass stems, but does not harm larger trees or wildlife. A prescribed burn is designed to mimic the natural fires that once occurred in prairie and savannah ecosystems. Fire-dependant ecosystems, such as Toronto's rare black oak savannah, contain prairie plants that respond positively to burning, and that grow more vigorously than they would in the absence of fire. These burns are a part of Urban Forestry’s long-term management plan to restore and protect Toronto’s rare black oak woodlands and savannahs.

ExpandWhy is black oak savannah important and where are they located in Toronto?

The black oak savannah habitat is extremely rare. It is estimated that only 1% of the original pre-settlement cover of prairie and oak savannah ecosystems remains in Ontario.

In Toronto, black oak savannah reminants can be found in South Humber Park, Lambton Park and High Park. High Park contains approximately 23 hectares of fragmented black oak savannah and is the most significant area of remnant prairie and savannah plant communities in the Toronto region. High Park has a healthy population of uncommon and rare savannah plants. This was recognized by the Province of Ontario when it was designated an Area of Natural and Scientific Interest (ANSI) in 1989. South Humber Park, Lambton Park and High Park are all classified as Environmentally Significant Areas (ESA).

ExpandWhy is the prescribed burn important for the black oak savannah?

Prior to settlement, wildfires were a natural occurrence. Prairies and savannahs have evolved to be fire-dependant and as a result, prescribed burns benefit native plants and animals by removing exotic plants and grasses, by restoring wildlife habitat, and by returning essential nutrients to the soil.

ExpandHow is it determined when a prescribed burn will be scheduled?

The Fire Boss visits the site 6 months prior to the burn to assess the area and review numerous factors, including the type of fuel on site (leaves, twigs, and stems), topography, proximity to park buildings and private property. After preparing the burn plan and reviewing it with pertinent City staff, the Fire Boss then begins a detailed study of weather conditions. City staff monitor rainfall daily and report this to the Fire Boss who will determine when the site is ready. The Fire Boss makes this decision by assessing the dryness of the site as well as forecasting the expected temperatures, humidity levels and wind patterns. From this information, the Fire Boss sets the burn date.

Since weather is difficult to predict with certainty, the time of the burn is set within 48 hours of the selected day in spring.  On the day of the burn, the Fire Boss has determined the appropriate time to set the fire so that it will remain under control, progress across the site at a “walking pace”, and so that it will give the desired effect of killing or setting back undesirable plants.

ExpandWho is responsible for setting and controlling the fire?

The City hires a highly trained Fire Boss who is qualified to carry out high-complexity burns in an urban environment. The Fire Boss and the trained crew are in charge of the technical aspects of setting and controlling the fire.  City staff are on-site to provide information about the prescribed burn and to monitor public safety.

ExpandWhy are only small areas of the park burned? Why not burn everything in one year?

Prescribed burns will ultimately enhance habitat conditions for the unique wildlife populations that rely on Toronto's savannahs, but while we work to improve this habitat we must be cautious of protecting the existing populations residing there. The natural habitat supports diverse insect and butterfly populations, as well as some breeding birds. It is not desirable to burn all the areas at once since this might destroy too much of one type of habitat in a given year. It is better to preserve unburned islands of habitat within the park for wildlife refuge.  Burning small patches also allows for periods of rest for vegetation to rebound and resprout before being burned again.

ExpandDo we need to keep burning every year?

We do not need to keep burning our savannah habitats every year. In the early stages, the burns were scheduled annually to compensate for the approximate 100 year break in the natural cycle of fires in Toronto. Now after approximately 10 years of burning Toronto savannahs, the program is being evaluated. Individual site features and habitat health will be taken into consideration, and burns will occur only as often as required to sustain conditions that support the growth of prairie plants.

ExpandHow will the burn impact park use?

Park users can expect limited access to the park during the prescribed burn. Temporary trail and road closures may be necessary in order to ensure public safety by keeping the public away from the active burn areas. Other areas that may be closed include parking lots, adjacent natural areas and other amenities.

Temporarily restricting access to these areas ensures that there will be fewer delays in completing the burn and will ease movement of burn professionals and City staff.

ExpandHow do fire-adapted species benefit from the prescribed burn?

Prescribed burns improve growing conditions for the fire-adapted plant species in numerous ways. When the leaf layer is burned off it is converted to ash and acts as a fertilizer that boosts plant growth. The blackening of the soil through the burn process increases light absorption from the sun and warms the soil which increases germination time and allows native plants to better compete with fast-growing invasive species.  Additionally, some seeds, such as acorns, have adapted to fire by producing a thick shell that requires fire to soften and weaken before germination can occur. Finally, burning the savannah is a method for controlling species that are not fire-adapted and that do not belong in a savannah ecosystem.

ExpandHow do wildlife respond to the prescribed burn?

The burn is usually scheduled during the early spring when many species have not yet emerged, or are not yet nesting. Staff comb the burn sites prior to ignition to ensure that people and wildlife are not present, any species remaining onsite will flee instinctually at the onset of smoke. Cavity trees that provide shelter and habitat for wildlife are protected and prevented from being burned.  Burns are small in scale and intentionally patchy, providing many small islands of refuge for other species to be sheltered.

ExpandHow do you determine the success of the burn?

The impact of the burn is determined by City staff who are trained in ecosystem management. Staff monitor the burn areas over many years and determine the positive and negative impacts on the different plant species. The desired effect is to see increased vigour and greater populations of prairie plants, while at the same time seeing reduced growth and decreased populations of invasive plants.

Increased oak regeneration is another key indicator of success. Studies undertaken in High Park in the 1970s and 1980s raised great concern over the lack of oak seedlings naturally regenerating. since many of the mature oaks in the GTA are in decline. In Toronto we are now seeing increased oak regeneration in areas that have received prescribed burn treatments.