Cathy Kavassalis – Canadian Coalition for Invasive Plant Regulation

But I Can Paint With Its Berries

Posted on 7 October 20267 October 2026 by Cathy Kavassalis

Invasive species: can reframing the problem become an excuse for inaction?

Of late, I have seen posts on social media and in the news casting invasive species as victims of human displacement, or describing their usefulness and suggesting we better recognize their value along with the harm they cause.

This reframing is, in part, a response to the militaristic language long used around invasive species—and I share that discomfort. But while reframing the problem can give us insights, it can also provide us excuses for inaction.

Let’s have a conversation, shall we?

Hello, emerald ash borer.

My, you are attractive, all that metallic green. And your surname? Agrilus. Well, welcome. I’ve met some of your relatives, the bronze birch borer and the two-lined chestnut borer. Sorry you accidentally got into that shipping crate. But you will find a home here. You will add to our diversity.

closeup photo of Emerald Ashe Borer — Adult Emerald Ash Borer
from https://inspection.canada.ca/en/plant-health/invasive-pests-and-plants/insects/emerald-ash-borer

Emerald ash borer has indeed added one species to Canada’s species count, yet it is harming a great many more. Near where the beetle first became established, in southeast Michigan, more than 99 percent of ash trees over 2.5 cm in diameter have been killed. At least 282 arthropod species feed on ash in North America, and at least 43 of them are native species that feed on ash alone. When the ash goes, they go with it.

Stopping emerald ash borer is no longer possible, but most would agree that slowing its spread, and keeping out other similarly harmful species, is essential if we want to protect the species and ecological relationships that are here. We generally agree on this course of action for species like emerald ash borer because we encounter them primarily through the harm they cause. We don’t spend much time asking what the beetle might offer us.

Yet we ask that question readily when the invasive species is a plant we chose to bring here through the horticultural trades.

Hello, buckthorn.

closeup of common buckthorn berries — Closeup of common buckthorn berries from https://www.invasivespeciescentre.ca/invasive-species/meet-the-species/invasive-plants/buckthorn/

My, you are attractive. Those glossy green leaves, those abundant dark berries. And your surname? Rhamnus. I’ll just move a few of you across the ocean and plant you in my garden. I’ve met your relative, alder-leaved buckthorn. She’s from here. You’re just another buckthorn. You will fit right into our landscape.

Except that isn’t quite how invasion biology works.

Common buckthorn (Rhamnus cathartica) isn’t simply another member of its genus taking its place in a hedgerow. It spreads and multiplies. It tolerates shade, grows quickly in the understory of woodlands, leafs out early and holds its leaves late into the fall.

Where buckthorn forms dense stands, it shades the forest floor, alters soil conditions and interferes with the regeneration of native trees. There is no dramatic moment of destruction. Nothing falls over. The next generation of the forest simply fails to appear.

We readily notice the vibrant buckthorn and its pretty berries, but we rarely notice the quiet absence of everything else. Yet those missing lives have value too.

Indigenous environmental scientist Jessica Hernandez writes, “we acknowledge them as displaced relatives rather than invasive species, since at the end of the day, they are also someone’s plant relatives.” She is describing her own community’s way of relating to these plants, and I offer it here with respect. It reminds us that these plants did not arrive on their own, and that everything here exists in relationship. But if we enlarge our circle of kinship to include introduced species, we must not accidentally shrink our circle of concern for everything already living around them.

Invasive species are not inherently “good” or “bad.” Buckthorn is not a villain, and caring for the land should not mean an endless war with pests and weeds. But neither does recognizing the value of species, or their relatedness, mean every organism should be allowed to reproduce and spread unchecked. We manage buckthorn because of what disappears when it spreads.

Integration?

Some of the voices arguing for a less militaristic response to invasive plants belong to people who know what it is to be the newcomer. They rightfully feel anxious about parallels between the language around invasive species and the demonization of human immigrants.

Artist Mayuko Fujino, who paints with pigments from buckthorn and other introduced plants, asks whether some invasive plants might integrate, as she did, with enough help. Here, there is an important distinction to be made. Many, if not most, introduced species do settle in with little harm. Others, like buckthorn, change the community around them faster than it can adjust. Over time new relationships will form, but many will be lost. Here we must seek an uneasy balance.

Fujino writes that decisions about what belongs are “sometimes… necessary,” but “deserve to be questioned.” I agree.

Benefits to whom?

finding a use for an
invasive species
does not make its spread
generally beneficial
Cathy Kavassalis

Our rules for introduced plants were shaped by the same settler values that first brought these plants here, values that treat plants as goods to trade, and they still allow new ones to be imported and sold regardless of how they impact other species. Those values deserve to be questioned.

Before a plant is designated invasive, authorities weigh its benefits against its potential harm to the economy, the environment and public well-being. Currently, that framework leans heavily toward protecting the marketplace and a gardening tradition, inherited with settlement, that values pretty plants over healthy ecosystems. The federal government’s long inaction on sales of Japanese barberry, which it acknowledges is invasive, is a case in point. We look for benefits so we don’t have to assume responsibility for a problem we caused.

But benefits to whom? The trunk of a dead ash can become a sculpture. An emerald ash borer can be a meal for a woodpecker. A buckthorn berry can give an artist pigment and be a meal for a bird. All of that can be true. But a benefit to an artist, or to an organism is not a benefit to the whole community, and finding a use for an invasive species does not make its spread generally beneficial.

photo of dead ash trees on Bruce Peninsula, Ontario Canada — A group of dead trees on the Bruce Peninsula. From **The Effects of Invasive Species on The Bruce Peninsula and How You Can Help** https://brucepeninsulapress.com/2025/10/07/whats-with-all-these-dead-trees/

The trouble is that humans are poor judges of slow consequences. The harm caused by emerald ash borer is easily visible: we watch the trees die. But ecological costs associated with invasive plants often arrive slowly, over decades, and fall on future generations outside our immediate sphere of care. We discount slow harm, with climate change and with invasive plants alike.

Emerald ash borer did not choose to cross the ocean; buckthorn did not choose to be planted. People made those choices. Because we bear the responsibility for their introduction, we bear the responsibility for what happens next.

For buckthorn, honouring that responsibility can be both practical and profound. It means learning to recognize it, noticing how its leaves stay stubbornly green in late fall after most native shrubs have dropped theirs. It means tending the land: pulling seedlings, seeking guidance on larger shrubs that resprout when cut, and planting native kin in the spaces left behind.

And before we add any new plant to a landscape, it means asking a generational question: are we willing to stay around to manage, heal and tend this landscape into the future?

Human responsibility

But individual care has limits. We cannot pull our way out of a problem that is still arriving and growing through trade. When emerald ash borer arrived, we regulated it, restricting the movement of firewood and ash wood.

For plants, we have been far slower. Many species known to be invasive can still be legally imported, sold and moved in Canada. If we are responsible for what we move, that responsibility belongs in law as well as in our gardens: preventing the import, sale and movement of harmful species, and requiring their management where it is possible.

So yes, paint with its berries. Make the ink. Admire the glossy leaves. Then take one more step, and pull the seedling coming up at the woodland’s edge.

Recognizing value does not equate with accepting harm.

Recognizing our relationships with other species means accepting responsibility for the impacts of our choices.

The tree seedling that never took root, the wildflower that lost its light, and the insects and birds that depended on them. They are relatives too.

Sources and further reading

Emerald ash borer

Herms, D.A. and McCullough, D.G. (2014). Emerald ash borer invasion of North America: history, biology, ecology, impacts, and management. Annual Review of Entomology 59: 13–30. Source for the ash mortality and arthropod figures, which it reports from Gandhi and Herms (2010), Biological Invasions 12: 1839–1846. https://doi.org/10.1146/annurev-ento-011613-162051

Canadian Food Inspection Agency (2026). Areas regulated for the emerald ash borer. Movement of ash firewood, logs, lumber and wood chips out of regulated areas is prohibited without CFIA approval. https://inspection.canada.ca/…/03-08/regulated-areas

Common buckthorn and barberry

Ontario Invasive Plant Council. Common buckthorn. https://www.ontarioinvasiveplants.ca/…/species/buckthorn/

Ontario Invasive Plant Council (2024). Common Buckthorn Technical Bulletin. https://www.ontarioinvasiveplants.ca/…/Buckthorn…

Knight, K.S. et al. (2007). Ecology and ecosystem impacts of common buckthorn (Rhamnus cathartica): a review. Biological Invasions 9: 925–937. https://doi.org/10.1007/s10530-007-9091-3

Schmidt, K.A. and Whelan, C.J. (1999). Effects of exotic Lonicera and Rhamnus on songbird nest predation. Conservation Biology 13: 1502–1506. Robins nesting in buckthorn and honeysuckle lost more nests to predators: a benefit to a bird that turns out to be a cost. https://scholars.ttu.edu/en/publications/effects-of-exotic-lonicera-and-rhamnus-on-songbird-nest-predation

Canadian Food Inspection Agency (2022). RMD-21-02: Pest risk management document for barberry (Berberis, Mahoberberis and Mahonia spp.) as a biological obstacle to the control of black stem rust (Puccinia graminis). States that Japanese barberry “is considered invasive in most of the eastern Canadian provinces (Nova Scotia, Ontario, Prince Edward Island and Québec)”, while regulating barberry for stem rust rather than invasiveness. https://inspection.canada.ca/eng/1653418602687/1653418603218

Indigenous perspectives

Hernandez, J. (2022). Fresh Banana Leaves: Healing Indigenous Landscapes Through Indigenous Science. North Atlantic Books. Free excerpt: https://www.rewildingmag.com/invasive-species-as-a…/

Arnold, C. (2025). How can we re-envision care for weeds? Indigenous weed management on the Shoalhaven River. People and Nature 7: 2334–2345. Open access. A relational ethic of care that includes careful removal. https://doi.org/10.1002/pan3.70138

Art and invasive plants

Fujino, M. (2026). For Integration, Against Demonization. Beakuency (Substack), March 24, 2026. https://beakuency.substack.com/…/for-integration…

Language and the wider debate

Reeb, R.A. and Heberling, J.M. (2025). Lost in translation: the need for updated messaging strategies in invasion biology communication. Plants, People, Planet 7: 536–545. Open access. Two invasion biologists on why war language and fear backfire, and why the science still holds. https://doi.org/10.1002/ppp3.10603

Davis, M.A. et al. (2011). Don’t judge species on their origins. Nature 474: 153–154. https://doi.org/10.1038/474153a

Simberloff, D. et al. (2011). Non-natives: 141 scientists object. Nature 475: 36. The reply to Davis et al.; best read as a pair. https://doi.org/10.1038/475036a

Richardson, D.M. and Ricciardi, A. (2013). Misleading criticisms of invasion science: a field guide. Diversity and Distributions 19: 1461–1467. Common objections and the evidence against each. https://doi.org/10.1111/ddi.12150

Fatal Attraction

Posted on 4 October 20267 October 2026 by Cathy Kavassalis

Fatal attraction: an intense draw to something that ultimately leads to disaster, destruction, or the end of a relationship.

photo of pitcher plant — Pitcher plants can lure insects and animals to their death. (Seguin, Ontario)

I marvel at the ingenuity of the plant world. Rooted in place, plants can’t go looking for food, seek a mate, or flee from herbivores. Instead, they have evolved extraordinary ways of getting other organisms to come to them.

Many plants enlist animals to carry their pollen, disperse their seeds, or provide defence. Flowers advertise with colour, shape and scent. Nectar, pollen and fruits provide rewards. These attractions benefit the plant and its animal visitors. Or not . . .

Not when a plant lures visitors into the arms of a waiting crab spider or ambush bug. And certainly not when the plant itself makes a meal of its visitors. We have several native carnivorous plants, like the purple pitcher plant (Sarracenia purpurea) and our sundews (Drosera spp.).

Sometimes, an attraction is an ecological trap.

A fatal case of mistaken identity

photos of dog-strangling vine and common milkweed — While milkweeds attract monarchs. Dog Strangling Vine (DSV) emits some of the same attractants. If monarchs have little choice, they will lay eggs on DSV, but that will never develop.
Click image to enlarge

Dog-strangling vine, also known as swallow-wort (Vincetoxicum spp.), is an invasive plant closely related to our native milkweeds (Asclepias spp.). Monarch butterflies sometimes lay their eggs on it, especially where milkweed is scarce. We don’t fully understand why, but cues shared with milkweed are the likely explanation.

The caterpillars hatch, begin to feed and die within days. For each egg laid there, it is a dead end.

Attraction and breeding success

But what happens when one plant is exceptionally good at attracting pollinators?

graphic of chemical compound in Buddleia davidii — Plants emit a use array of chemical signals. Buddleja davidii is particularly good at scents that are alluring to butterflies, including some pest species like the cabbage white.

Consider butterfly bush, Buddleja davidii. Its reputation as a butterfly magnet is well deserved. The plant produces volatile organic compounds such as 4-oxoisophorone and oxoisophorone epoxide that lure butterflies to its floral rewards. The plant is an extraordinarily effective advertiser.

info graphic showing impacts of invasive plants on native pollinators and native plants — When invasive plants are introduced, they can disrupt pollination networks. Affecting both plant reproduction and pollinator reproduction.
**click image to enlarge**

And for the butterfly bush, that is a very successful strategy. Butterfly bush, because it does not readily self-pollinate, depends on insect visitors for reproduction. More visits can mean more opportunities for pollination and seed production.

It can produce enormous numbers of small, winged seeds that are dispersed by wind and water. Long flowering periods, prolific seed production, easy germination, and vigorous growth have all contributed to its ability to establish beyond cultivation and become invasive in many parts of the world. Its attraction is part of its success, sometimes at the expense of other species.

A relationship breaker?

flora nectar and the microbial communities that shape plant/pollinator communities.
**click image to enlarge**

A pollinator doesn’t live on a single plant. It lives in a community of plants.

When one plant commands attention, what happens to the others?

Competition for pollinators does matter. Purple loosestrife (Lythrum salicaria), a familiar invader of Ontario wetlands, has been found to draw pollinators away from its native relative, winged loosestrife (Lythrum alatum), reducing visits and seed production in the native plant. Research has also found that where purple loosestrife is abundant, the native monkey-flower (Mimulus ringens) produces fewer seeds.

An irresistible neighbour like purple loosestrife can quietly change which plants get pollinated and which don’t. Which plants reproduce well, and which don’t.

Are plants that attract pollinators good for pollinators?

To be honest, some plants are jerks. Some advertise rewards and then fail to deliver.

Here’s a new word for you: pseudoanthery, or fake anthers. Begonias produce separate male and female flowers on the same plant. The male flowers offer pollen as a reward. The female flowers offer nothing (no sweet treats), but their stigmas mimic the pollen-laden anthers of the males, fooling pollen-collecting bees. Researchers call this intersexual mimicry.

The plant saves resources while still producing enough genuine pollen to keep pollinators coming. It’s deceptive, but not fatal.

However, even when a plant genuinely provides abundant nectar or pollen, abundance tells us little about quality.

Microbes interact in complex way with pollinators and plants. Communities change over time.
**Click image to enlarge.**

We often talk about nectar as if it were simply sugar water. It isn’t. Nectar is a complex and changing mixture of sugars, amino acids, minerals, and secondary compounds. It can also harbour yeasts and bacteria that alter its chemistry and scent, potentially influencing the behaviour of the animals that consume it.

Pollen varies considerably in nutritional composition too. Different plants provide different amounts and proportions of proteins, amino acids, lipids and other nutrients. Some pollen even contains toxins that deter palynivory (pollen consumption).

So an alluring scent and abundant nectar or pollen don’t tell us the whole story. A plant can be very good at getting a butterfly, bee or bird to the table without necessarily providing everything that creature, or its offspring, needs.

Beyond counting visitors

We celebrate plants covered in bees, butterflies or birds. We count the visitors, photograph them and call the plants pollinator-friendly or bird-friendly.

But attraction is only the first measure.

Perhaps some better questions :

Which species does it serve, and what are they consuming?
Does it support their offspring?
What does it replace or displace, in the garden and beyond?
Does it meet the needs of a diversity of species, or mainly the species we happen to notice?
Could a different plant, one that belongs to the ecological community of this place, provide the same or greater benefit?

We don’t have all the answers, but asking questions and seeking answers is important.

We know that plants can reshape pollination networks, but we know far less about how our garden choices might affect resource quality and communities of life over time.

Is attractiveness a virtue?

In nature, attraction is a strategy. Sometimes it leads to pollination. Sometimes it leads to predation or deception. And sometimes it reshapes relationships we barely notice.

We are attracted to pretty plants. And when those plants attract butterflies, bees or birds, so much the better. But attraction does not always lead to positive ends.

If our attraction to a plant ends up displacing other plants, disrupting ecological relationships or spreading an invasive species, perhaps we should ask ourselves:

Is this a fatal attraction?

Some reading for the curious

Dog-strangling vine and monarchs

Casagrande, R.A. and J.E. Dacey. 2007. Monarch butterfly oviposition on swallow-worts (Vincetoxicumspp.). Environmental Entomology 36(3): 631–636. https://academic.oup.com/ee/article/36/3/631/406797
Mattila, H.R. and G.W. Otis. 2003. A comparison of the host preference of monarch butterflies (Danaus plexippus) for milkweed (Asclepias syriaca) over dog-strangler vine (Vincetoxicum rossicum). Entomologia Experimentalis et Applicata. https://onlinelibrary.wiley.com/…/j.1570-7458.2003.00049.x
Ontario Invasive Plant Council. 2025. Dog-strangling Vine Technical Bulletin. https://www.ontarioinvasiveplants.ca/…/Dog_Strangling…

Butterfly bush

Lehner, M.S., S. Schulz and S. Dötterl. 2022. The mystery of the butterfly bush Buddleja davidii: How are the butterflies attracted? Frontiers in Plant Science. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.994851/full
Tallent-Halsell, N.G. and M.S. Watt. 2009. The invasive Buddleja davidii (butterfly bush). Botanical Review. https://cfpub.epa.gov/si/si_public_file_download.cfm…

Competition for pollinators and invasive plants and pollinator networks

Brown, B.J., R.J. Mitchell and S.A. Graham. 2002. Competition for pollination between an invasive species (purple loosestrife) and a native congener. Ecology 83: 2328–2336. https://esajournals.onlinelibrary.wiley.com/doi/10.1890/0012-9658(2002)083%5B2328:CFPBAI%5D2.0.CO;2
Flanagan, R.J., R.J. Mitchell and J.D. Karron. 2010. Increased relative abundance of an invasive competitor for pollination, Lythrum salicaria, reduces seed number in Mimulus ringens. Oecologia. https://link.springer.com/article/10.1007/s00442-010-1693-2
Stout, J. C., & Tiedeken, E. J. 2017. Direct interactions between invasive plants and native pollinators: evidence, impacts and approaches. Functional Ecology, 31(1), 38-46. https://besjournals.onlinelibrary.wiley.com/…/1365-2435…
Losapio, G., Fortuna, M.A., Bascompte, J., Schmid, B., Michalet, R., Neumeyer, R., Castro, L., Cerretti, P., Germann, C., Haenni, J.P. and Klopfstein, S., 2019. Plant interactions shape pollination networks via nonadditive effects. Ecology, 100(3), p.e02619 https://esajournals.onlinelibrary.wiley.com/…/ecy.2619

Deceptive flowers

Castillo, R.A. et al. 2012. How to cheat when you cannot lie? Deceit pollination in Begonia gracilis. Oecologia. https://link.springer.com/article/10.1007/s00442-012-2250-y
In Defense of Plants. Pseudoanthry. https://www.indefenseofplants.com/…/2017/1/25/pseudoanthry

Nectar, pollen and nutrition

Barberis, M., et al., 2024. Floral nectar: fifty years of new ecological perspectives beyond pollinator reward. Perspectives in Plant Ecology, Evolution and Systematics, 62, p.125764. https://www.sciencedirect.com/…/pii/S1433831923000483 Vannette, R.L. 2020. The floral microbiome: plant, pollinator, and microbial perspectives. Annual Review of Ecology, Evolution, and Systematics 51. https://www.annualreviews.org/…/annurev-ecolsys-011720…
Vaudo, A.D., J.F. Tooker, C.M. Grozinger and H.M. Patch. 2015. Bee nutrition and floral resource restoration. Current Opinion in Insect Science 10: 133–141. https://www.sciencedirect.com/science/article/abs/pii/S2214574515000875
Rivest, S. and J.R.K. Forrest. 2020. Defence compounds in pollen: why do they occur and how do they affect the ecology and evolution of bees? New Phytologist 225: 1053–1064. https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.16230