Native, Invasive and Nuisance Species

Invasive species have been silently invading our local ecosystems for decades.  When their populations remain undetected for too long, the damage they cause can be irreversible.  Today, invasive species are everywhere across the globe, and they are the second most significant threat to biodiversity [1].  Invasive species may not seem threatening to those who cannot recognize or identify them, but once you learn about invasives you will begin to notice them everywhere you go.  Invasives threaten not only the environment, but also society and our economies.    

Native Swamp Milkweed Asclepias incarnata

So, what are native, non-native and invasive species?  These three terms are the building blocks in understanding the basics of invasive species.  Native species have naturally occurred in a particular region, ecosystem or habitat without human introduction [2].  Over thousands of years, these species have formed “symbiotic”  relationships with other species.  These symbiotic relationships may be mutually beneficial like bees pollinating flowers, or even one-sided and parasitic like a leech that attaches to a fish.  Food webs are the result of delicate relationships amongst species.  For example, a native berry bush feeds native songbirds in the winter and they have evolved to survive with each other.  The native berry bush benefits from this relationship because birds will disperse its seeds in their poop, while these birds can count on the berry bush as a food source during the harsh winters. Typically, native species exist together and provide one another with habitat, food, and other services for each other. 

In recent years, gardening for aesthetic and ornamental purposes has grown in popularity.  Societal norms have pressured perfect lawns and manicured gardens.  Intrusive plants that weren’t intentionally planted are removed and labeled as a nuisance, or weed.   What makes a weed, a weed? Is it any unwanted plant in gardens, or is it a native plant thriving in its preferred habitat?  Many societal views have skewed our understanding of native plants.  Instead, we should be praising our native plants for their ecological benefits.  Within our shoreland environments, native plants offer economic, environmental and societal benefits that ensure sustainable living.  

It is important to note that non-native, invasive plants should be managed and controlled.  Invasive species are threatening our ecosystems and outcompeting native species. Check out these important native species that are commonly mistaken as unwanted weeds!

An invasive species is one that has established in a new area, but evolved in other regions across the world, or perhaps even in a different area of the same country [3].  These species have been transported beyond their native range, often by human activity. For instance, invasive alien species can be transported in the ballast water of ships, moved across the world in the wood of shipping pallets or even sold at plant nurseries as garden ornamentals.  Today, international trade is common across many countries which involves shipping goods across the world, with potential invasive hitchhikers.  The most successful invasive species share common characteristics [1].  Invasives typically have high rates of reproduction, meaning they produce high amounts of seeds or offspring, which allow these species to grow quickly in population.  There are often few natural predators and diseases of invasive species in new environments which allow their populations to flourish.  Lastly, many invasive species are extremely adaptable to various habitats and climates, increasing their survival rate. Due to these reasons, invasive species can dominate native habitats and can quickly spread to new areas.  An example of an invasive species is Phragmites, which originates from Asia and Europe.  It grows in dense stands that chokes out native plants and doesn’t provide habitat for wildlife [4].  

Invasive Common Reed Phragmites australis

However, there is a difference between invasive and non-native species, and these terms cannot be used interchangeably.  All invasive species are non-native, but not all non-native species are invasive.  For a species to be invasive, it must cause harm to the environment, economy, or society.  Many non-native plants do not cause harm, and simply exist beyond their native range [5].   An example of a non-native species is a tomato plant; it originates from outside of Ontario, but it grows here without causing harm to species.

Nuisance species may be native or non-native species, but they share the trait of causing harm to ecosystems, economies or human health [6].  Nuisance species cause annoyance or inconvenience to humans for unique reasons that depend on the species. Common examples include poison ivy and Canadian geese.  While both of these species are native, they cause harm in one way or another.  Poison Ivy can cause a rash if someone brushes up against its leaves.  Canadian geese, in large populations, can be a nuisance as well because they defecate on property owner’s lawns, and can be aggressive when protecting their young.   

Why are native species so important?  Native species support each other in ways that are not possible for invasive species [7]. Without native species, ecosystems could collapse due to biodiversity loss and shrinking habitat.  Native species are critical to any functional and thriving ecosystem.  The native wildlife, insects and plants that we enjoy today are the result of intricate and long-lasting interactions between each other.  For example, many species of native wildlife depend on native vegetation to survive.  If that native plant were to disappear, the native wildlife that it supports may disappear as well.  An example of this is the decline of Monarch Butterflies due to mass removal of Milkweed.  Milkweed species are the only host plant for Monarch Butterflies, and without it, Monarchs suffered a dramatic population decline.  

Invasive species present a challenge that not one individual alone can conquer.  A community-based approach is necessary to manage invasive species.  It is important to note that completely eradicating all invasive species is impossible.  Instead, we can manage populations with various control methods.  There are many municipalities, conservation authorities and environmental groups working towards managing invasive species across Ontario.  If you are interested in helping with the fight on invasive species, you can volunteer with community groups that have created programs to manage invasive species, such as The Land Between.  To learn more about shoreland invasive species and their control methods, click here.

Works Cited

[1] Government of Canada. (2017 May 12). Why invasive alien species are a problem. Retrieved from

[2] The National Wildlife Federation. Native Plants. Retrieved from

[3] Rutledge, K., Ramroop T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., Costa, H., Hall, H. and Hunt, J. (2011 March 24). Invasive Species. National Geographic. Retrieved from

[4] Ontario’s Invading Species Awareness Program. (2021) Invasive Phragmites: Phragmites australis. Retrieved from

[5] National Park Service, U.S. Department of the Interior. (2020 December 3). Invasive and Non-Native Species. Retrieved from

[6] Gwise, S. (2021 October 29). Invasive and Nuisance Species. Cornell University. Retrieved from,causing%20ecological%20and%20economic%20harm.&text=Nuisance%20species%20may%20be%20native,poison%20ivy%20and%20Canadian%20geese.

[7] U.S. Fish and Wildlife Service (2019 October 28). Native Species Conservation. Retrieved from

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