The City of Toronto maintains planted and naturalized areas through best management practices such as forest thinning, prescribed burns and controlling invasive plant species. Those practices create healthy forests that provide many environmental benefits. Learn how you can help and what to expect when forest management operations are happening in your area.

Pollution, construction, erosion and other factors deteriorate our natural habitats, and invasive species take advantage of the disturbance to thrive. Invasive species compete with native plants for growing space and nutrients. Please keep in mind that Invasive species management on public land is done by UF qualified staff only.

What you can do to help


  • Plant native plants instead of non-native and invasive ones on your property.
  • Know if you have invasive plants on your property.
  • Use Waste Collection Services to dispose of garden waste and compost.
  • Know where your topsoil/other fill material comes from and that it’s not a source of invasive seeds.
  • Stop seeds from germinating in disturbed soil by:
    • minimizing tilling and digging on your property
    • keeping pets on leashes
    • staying on designated trails in parks


You may need a permit to Injure or Remove a Tree.

Plant Type Method: Manual Control Method: Chemical Control
Herbaceous Annual or Biennial

(Garlic mustard, Himalayan balsam, tall sweet white clover, burdock)

hand pull or cut close to the base when flowering only in extreme circumstances
Herbaceous Perennial

(Dog-strangling vine periwinkles, Japanese knotweed, goutweed)

  • hand pull or dig out roots
  • cut repeatedly to weaken roots
  • smother with mulch or black plastic
apply herbicide using spray bottle or sponge:

  • to leaves
  • cut stems of large plants

(Norway maple, Manitoba maple, white mulbery, Siberian elm, white poplar, common buckthorn, tartarian honeysuckle, burning bush, Asiatic bitterwseet, riverbank grape)

  • hand pull or dig up smaller stems
  • cut large vines at base
  • girdle large stems of trees/shrubs
cut stems and apply herbicide to stem


Cosmetic use of pesticides is prohibited unless authorized by a permit from Ministry of Environment, Conservation and Parks.

In response to the COVID-19 pandemic, the City will not undertake a prescribed burn in High Park and South Humber Park in 2021.


A prescribed burn is a deliberately set and carefully controlled fire. It burns low to the ground and consumes dried leaves, small twigs and grass stems but does not harm larger trees. It encourages the growth of native savannah vegetation and sets back the growth of undesirable invasive species.

Prescribed burns are:

  • Planned and lead by a highly trained Fire Boss.
  • Controlled by the Fire Boss and a trained crew so the prescribed burn:
    • progresses at a walking pace
    • removes invasive/exotic species
    • remains under control
  • Used on small areas of land to ensure the survival of habitats for birds, butterflies and insects.

During prescribed burns:

  • onsite City staff provide information about the burn and ensure public and wildlife safety
  • park users should be prepared for restricted access to areas near burn sites, including temporary road closures, trail closures and reduced parking
  • smoke from burns will rise and dissipate in ideal conditions, however, weather changes could cause smoke to drift and impact residential areas near the park(s)
  • close windows or consider leaving the area to avoid potential sensitivity to smoke

Why we have prescribed burns

Toronto is home to the rare black oak savannah ecosystem. Only 1% of this ecosystem remains after human settlement. This ecosystem can be found in High Park, Lambton Park and South Humber Park.

High Park contains about 23 hectares of fragmented black oak savannah and is the most significant area of the savannah ecosystem in Toronto.

Prior to European settlement, the landscape was defined by Indigenous Peoples’ use of controlled burns to manage the landscape, coupled with naturally-occurring wildfires. Indigenous people would use fire to clear the land for agriculture, to rejuvenate the quality and quantity of forage and medicinal plants, and to attract wildlife. This use of fire also helped to regenerate and maintain savannah habitats. Prescribed Burns are designed to echo these historic controlled and natural fires and benefit native plants and animals by reducing invasive/exotic plants and grass, stimulating native plant regeneration, restoring wildlife habitat and returning nutrients to the soil.

Access to the park(s) and its facilities may be limited during a tree thinning. Trails will be cleared of debris but most downed trees will remain to decompose and contribute to the health of the forest.

Tree thinning is a selective removal of trees and shrubs from a densely planted area so that the remaining trees will have better access to growing space, light, water and other nutrients.

During a tree thinning:

  • downed trees will be left behind to decompose unless doing so will be unsafe or cause problems
  • most sites will be replanted with new native trees and shrubs
  • invasive/exotic plants will be prevented by the use of herbicides
    • signs will be posted if herbicides are used

Sites may look different after tree thinning.

Why tree thinning is done

Succession is the natural process of replacement of one group of plants by another group of plants in an area over time. Species that are more tolerant to shade will naturally replace the species that are fast-growing and less shade tolerant.

Tree thinning mimics succession. In the City of Toronto, thinning will be implemented in the areas that were densely planted with a mix of sun and shade-loving trees. Short-lived, sun-loving trees such as poplars provided habitat for the growth of long living, shade-loving trees such as oaks and maples.

Once the long living species become well established, the short-living species are removed to reduce the competition for growing space and promote the growth of the shade-loving species.

The Ontario Ministry of Environment, Conservation and Parks Cosmetic Pesticide Ban limits the use of pesticides by homeowners for cosmetic uses. There are exceptions for forestry management, arboriculture, health and safety, and natural resource management. Application of pesticides under these exceptions will require the services of a licensed exterminator.

The City of Toronto uses herbicides under the natural resources management exception to manage larger areas infested by aggressive invasive species that can’t be managed manually.

The City of Toronto uses two Class 9 pesticides regulated by the Pesticides Act.

Roundup Weathermax is the primary herbicide used by the City. It is considered non-toxic.

Garlon RTU is used for species that don’t respond to Roundup Weathermax. It is particularly good for roots. This herbicide can also be used in colder weather. It has a low-toxicity.

Coloured dye is mixed with the herbicides to indicate where it has been used. City staff will post signs indicating the area that has been treated. Please follow the instructions on the signs until they have been removed.

Pesticide use is regulated. Any use of pesticides (including herbicides) is prohibited in the city of Toronto and homeowners shall focus on manual methods of invasive species management.