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Invasive Species Management

Invasive species are plants and animals that spread rapidly, often displacing native flora and fauna and causing harm to surrounding environments. Invasive species are often alien or exotic, having been introduced through human activity to areas outside of their natural range. Invasive species can often be characterized by a few traits that result in their high success rates in new habitats. These traits include resilience to disease and pests, hardiness (well adapted to many climatic and soil conditions) and a high reproductive rate with high viability of offspring. Invasive species can have highly damaging effects on new habitats as they alter natural ecosystem functions. They also often have negative impacts on biodiversity as they form monocultures that replace all diversity within an area. Biological invasion by alien species is second only to the destruction of natural habitats as the leading cause of biodiversity loss!

The Toronto Zoo is a leader in animal and plant conservation. As such, there is an emerging Invasive Species Management Program. This program encompasses continuing research, education and management initiatives to help prevent and control the spread of invasive species.

Canada Goose (Branta canadensis)



A large population of Canada Goose remains on Zoo grounds throughout the year and causes detrimental eutrophication in our waterways. Goose feces is either directly deposited into waterways or it leaches in via rain and run-off. The Toronto Zoo is currently managing the growing population by removing all goose eggs on site. Several techniques have also been used to eliminate or decrease the goose population have been attempted, including:
  • A laser gun: a concentrated red laser beam projected towards the geese, aimed to intimidate the birds; a non-invasive deterrent
  • Egg-oiling: In the spring, all nests are located and eggs are oiled. This method has substantially decreased the number of goslings on-site
  • Horticulture staff and volunteers planted trees and shrubs along the waterway to reduce the movement of geese from the waterway to the pathways during moulting season. Since Canada geese prefer open grassy areas, the number of geese can be reduced on site by creating natural areas with meadows and forests.


Garlic Mustard (Alliaria petiolata)



What is it?
  • An invasive species; the UN has proclaimed invasive alien species as the second leading threat to biodiversity globally.
  • Garlic mustard is a member of the mustard family and originates from Europe and parts of Asia and Africa
  • The biennial plant was introduced to North America in the 1860s where it was used for culinary and medicinal purposes.
What's the big deal?
  • Garlic mustard, when established, has the ability to greatly alter the soil composition, killing off mycorrhizal fungi communities that are necessary for native plant growth and success. (This plant displaces and strangles native vegetation and tree saplings)
  • This alteration results in the loss of native flora and domination of garlic mustard, leading to the creation of monocultures. Unlike in their native ranges, there is a lack of herbivory which greatly increases their competitive ability and subsequent chance of survival.
  • Garlic mustard populations in the Great Lakes basin has exploded in the last 10-20 years, and many woodland areas are threatened
What is being done at the Toronto Zoo?

Garlic mustard has become a prominent species within the Rouge Park and Toronto Zoo site. A scientifically approved management technique is to pull the plants during the flowering period in mid-May, and continue to do so until the seed bank is exhausted. Seeds remain dormant in the soil for 5 years. Disturbed soil should ideally be replanted with native ephemeral flowers, shrubs and tree species.

In 2009, the Zoo and community partners pulled over 4200 pounds of Garlic Mustard in the Annual Garlic Mustard Pull! The following day a group of high school students joined CER and Horticulture staff and planted 350 native ephemeral flowers, several shrubs and a ceremonial tree.

In 2010, the Zoo and partners from Symcor, TELUS, XEROX, Leaf (Local Enhancement and Appreciation of Forests), Seaton House, University of Toronto and Anishinaabe First Nation Elders, pulled 4 tonnes of garlic mustard out of ~12Ha of the Core Woods area of the Zoo (a relative fragment of the Rouge Park) and replaced with over 750 native shrubs and forest plants.

With continuing efforts for the next several years the Toronto Zoo hopes to significantly reduce the garlic mustard population within the zoo.










Dog Strangler Vine (Vincetoxicum rossicum)



What is it?

Dog-strangling vine (DSV) or Pale Swallow-wort is:
  • An herbaceous perennial native to Ukraine and Parts of Russia.
  • Member of the Milkweed Family.
  • DSV spreads rapidly as it reproduces through seed dispersal and rhizome growth.
What's the Big Deal?
  • DSV is found in areas where there have been moderate disturbances and where gaps in the canopy allow DSV colonies to establish.
  • These vines are aggressive, forming dense colonies and choking out other flora such as trees and shrubs.
  • Dog-strangling vine populations thrive because there are no native species present to consume and control them. An effective method for DSV removal has not yet been determined. However, both mechanical and chemical control strategies are used to help limit the spread of species.
What is being done at the Toronto Zoo?

The Toronto Zoo in partnership with several universities is conducting studies on site to quantify mechanical and biological removal applications for DSV. These studies will hopefully give insight into better management methodology of DSV in the Toronto Zoo site and surrounding areas. DSV samples are currently collected from the Toronto Zoo and Highland Creek (University of Toronto Scarborough) to be used in research. In some situations pesticides must be used to buffer our native plant and woodland areas from the threat of DSV monocultures.




Phragmites or Common Reed (Phragmites australis)



What is it?
  • Phragmites or Common Reed (Phragmites australis) is a large perennial grass that is found in wetlands and riparian zones. Although there are native species of Phragmites they are not nearly as invasive and vigorous as the European strain, which has steadily replaced the native.
  • The common reed is also known to distribute itself through rhizomes and seeds.
What's the Big Deal?
  • The invasive strain has been subject to scrutiny because it has been known to alter dune ecology by choking out native flora, contributing to the degradation of wetlands in Ontario.
What is being done at the Toronto Zoo?
  • Management of the invasive phragmites often proves challenging because it is very difficult to distinguish between native and non-native strains. The Toronto Zoo is currently developing a website that allows land owners to identify and help manage the invasive phragmites population in Canadian wetlands.






Rusty Crayfish (Orconectes rusticus)



What is it?
  • Rusty Crayfish (Orconectes rusticus) is another extremely invasive organism that has had profound affects on the Great Lakes.
  • Rusty crayfish, which are native to the Ohio River Basin, U.S., were introduced to Ontario and the Great lakes in the 1960s.
What's the big deal?
  • These introductions have lead to the displacement of native crayfish. Rusty crayfish are very aggressive out-competing smaller more docile native crayfish for food and territory. This displacement of native crayfish reduces food for other organisms such as fish and waterfowl which feed on them.
  • As well, Rusty crayfish have been found to eat very large portions of aquatic plants as their metabolisms are much higher than those of native species. This 'clear-cutting' of aquatic plant beds has major impacts on the water ecology.
What is being done at the Toronto Zoo?
  • The Toronto Zoo has developed a crayfish identification guide to aid land owners and community members in identifying and reporting exotic crayfish species in an attempt to prevent and control exotic crayfish populations.


Photos Taken by: D. Lawrie