Imagine walking through a forest and hearing nothing but the soft crunch of fallen needles and dry twigs beneath your feet. “You notice the underbrush and poplar are missing; these are the unwanted species for the forestry industry (…) Even the songbirds are absent.” Eerie, isn’t it? This is how lifelong trapper, hunter, and fisherman, Robin Horwath, along with other trappers in Ontario, have described a forest after it has been aerially sprayed with herbicides from helicopters.
Aerial spraying of herbicides violates the Treaty rights that are recognized and affirmed in section 35(1) of the Constitution Act, 1982 (1). Herbicides also contaminate plants, which are then consumed by animals and humans.
Herbicides are generally used to inhibit the growth of “unwanted” plants. One of the most common herbicides in Canada is Roundup which is produced by Bayer. Roundup contains an active ingredient called “glyphosate N-(phosphonomethyl) glycine”, and these glyphosate-based herbicides are typically sprayed onto foliage and are absorbed through leaves (2). Glyphosate inhibits plant growth by traveling through the water- and sugar-conducting tissue in plants, disrupting metabolic processes. This disruption often results in leaves that are yellow, smaller, wilted, or dead (3). Therefore, glyphosate is considered by some within Ontario’s forestry industry as an effective tool to inhibit the growth of “unwanted plants”.
Not only does glyphosate inhibit plant growth, but it stays in the environment for at least one year (4). The Traditional Ecological Knowledge Elders Group (of the North Shore of Lake Huron in Ontario, Canada) states, “In the weeks and months that they persist in the environment, glyphosate-containing herbicides and their derivatives can do significant damage to humans and non-humans. We know this from first-hand knowledge of our territories and the ecological relationships of which we are a part (1).” If glyphosate is known to damage the environment and living beings, why does the forestry industry continue to spray glyphosate?
The forestry industry sprays herbicide on saplings to reduce competition posed by deciduous trees and herbaceous plants to the conifers that are used for pulp and paper. These deciduous plants shade out conifers because deciduous plants use their broad-leaves to capture more sunlight in the spring and summer than conifers such as pine trees. Removing competition provides the typically slower-growing conifer trees with more space and sunlight to grow, which in turn reduces the time needed before harvesting, and also makes accessing trees easier to maximize profits for the forestry industry. Further, using helicopters to aerially spray herbicides is more efficient and economical than target spraying on the ground (5). However, the public is coming together to advocate for an end to glyphosate spraying in forestry because the profit to the forestry industry and the herbicide manufacturer(s) are not worth the vast and compounded costs to the environment and living beings.
One impact of aerially spraying herbicides that must be accounted for is the displacement of wildlife species. “People are noticing moose numbers are down,” says Robin Horwath. “They’re killing off tender shoots like poplar. This is the feed that moose need. Big pine and red pine don’t support moose habitat.” In fact, fewer sightings of many large wildlife species have been described by multiple people after glyphosate was sprayed in Ontario’s forests (6, 7).
In addition to personal accounts, a scientific study has observed similar patterns : A three-year study on moose presence also found that there were fewer moose in areas that were sprayed with glyphosate. Biologists tested whether aerially sprayed glyphosate decreased forage resources and overwinter utilization by moose at four glyphosate-sprayed and control (unsprayed) plots near Thunder Bay, ON (2). Prior to spraying, moose presence was similar between sprayed and control plots. However, after spraying occurred, biologists observed more groups of moose tracks on control plots (areas that were not sprayed) and fewer groups of moose tracks where the herbicide was applied. Even more notably was that one year after the study, moose still consumed more vegetation in control plots; up to 32 times more vegetation. This access to food also translated into twice as many moose pellets in control plots compared to plots that were sprayed with glyphosate (2). The researchers concluded that there was more vegetation available in the control areas, and this availability meant that moose did not have to expend as much energy searching for food. These findings are in agreement with observations from several individuals, and suggest that glyphosate reduces the vegetation available to many wildlife species, not just moose, that rely on herbaceous and broadleaved plants in sprayed areas.
But there is more. Additional studies have reported a reduction in vegetation at sprayed areas after several years post-spray. Within two to three years after spraying herbicides, some species begin to return (8); however, the growth of some plant species is not equal to habitat recovery. This is because habitats that are sprayed do not readily return to pre-spray levels of diversity and ecosystem productivity.
Yet another major concern is the persistence of glyphosate residues in the environment, and whether high or chronic exposure to glyphosate is toxic to humans and other mammals (1, 9). Two recent studies have found that glyphosate residues do not simply disappear, but they persist in plant tissue. One study detected glyphosate residues in fireweed (Chamaenerion angustifolium) root samples twelve years after a glyphosate treatment (18). Another recent study assessed the persistence of glyphosate in vegetation and found that glyphosate residues can remain in vegetation for at least one year after aerial spraying (4). Animals including moose, white-tailed deer, and black bear are capable of consuming enough vegetation to exceed the acceptable daily intake established by Health Canada (4). For example, a 50 kg white-tailed deer can consume 2.4 kg of vegetation per day, but only needs to consume 0.78 kg of vegetation containing glyphosate to exceed the acceptable daily intake for glyphosate residues (4). However, this latter scenario only accounts for residue levels within the first 18 days of aerial spraying, and these levels decline over time (4). Therefore, according to some researchers, it is unlikely that any species in this study would consume enough glyphosate residues over a lifetime to experience detrimental health effects. Despite the observed decline of glyphosate levels in vegetation (4), a review of several research studies examined the immediate effect that glyphosate can have on the microbial health of animals (10). The review explains that glyphosate generally reduces a plant’s resistance to root pathogens which can alter the microbial community within plants. These plants may then be consumed by animals (such as forage for moose), introducing the microbes in the plant into the animal’s gut. Changes to the animal’s gut microbiome can affect the immune system of animals, ultimately impacting their health. This shift in microbe communities increases the susceptibility of insects, birds and mammals to harmful bacterial pathogens. The authors state that more studies are needed to determine the possible effects of sub-lethal exposure to glyphosate such as carcinogenicity and reproductive toxicity, among other effects (10). But contrary to the previous study (4), these authors conclude that the consumption of glyphosate residues is associated with detrimental health effects, and that the accumulation of glyphosate in the environment is related to outbreaks of several plant and animal diseases (10).
In addition to animals, exposure to glyphosate can be harmful to humans. Researchers have also measured glyphosate residues in blueberries and plants used for traditional medicine by Indigenous people. Plants used for traditional medicine contained glyphosate residues exceeding levels set by Health Canada for at least one month after glyphosate was sprayed (4). These plants included goldenrod (Solidago spp.), pearly everlasting (Anaphalis margaritacea), raspberry (Rubus idaeus) and sweet fern (Comptonia peregrina). The authors explain that the largest risk to human health in regards to aerial spraying is when fruit is consumed without washing within 18 days of spraying. The risk increases when this exposure to glyphosate is repeated throughout one’s lifetime (4). Another study measured glyphosate residues in fruit samples one year after glyphosate treatment, and found that 26% of raspberries contained glyphosate residues that still exceeded Health Canada guidelines (18).
In 2015 the World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate as “probably carcinogenic to humans” (9). One type of cancer that has been clearly linked to exposure of glyphosate-based herbicides is non-Hodgkin lymphoma (9). At least 42,000 people have filed lawsuits against Bayer (formerly known as Monsanto) alleging that exposure to Roundup caused them or their loved ones to develop non-Hodgkin lymphoma (11). In the 2018 court case of Dewayne “Lee” Johnson v. Monsanto Company, Johnson won $78 million in damages from Monsanto after he developed non-Hodgkin lymphoma after an extremely high exposure to Roundup while working as a landscaper. The jury ruled that Monsanto was responsible for negligent failure, and that Monsanto knew or should have known that Roundup is dangerous.
During the court case, Monsanto’s internal documents were released. An investigative report into Monsanto’s internal documents by CBC/Radio-Canada revealed that Monsanto employees hired an Ontario firm to recruit researchers to publish studies that defended glyphosate (12). In total, fifteen researchers published five studies and one review; all of which unanimously concluded that glyphosate was not a carcinogen (12). The authors later signed a correction clarifying that Monsanto reviewed a preliminary and final draft of their article and apologized for any “errors or omissions” in the original papers (Williams 2018). Additionally, Monsanto directly paid two of the researchers through existing consulting contracts (13). CBC/Radio-Canada’s investigation also revealed that these studies were cited in Health Canada’s reference list for its re-approval of glyphosate in 2017 (14). Doctors, academics and medical groups requested that Health Canada organize an independent panel to review its re-approval decision, which Health Canada rejected and has stated that they considered 1,300 studies in its re-approval decision (12). Health Canada’s selection of these studies have also been criticized because many studies were funded by industry (12). Despite the controversy, Bayer maintains that its glyphosate-based herbicide, Roundup, is safe. However, the jury and others would likely suggest otherwise based on the outcome of the Johnson v. Monsanto Company lawsuit and the fact that numerous municipalities worldwide have restricted or banned the use of glyphosate (15).
While Ontarians continue to live with the effects of aerially sprayed glyphosate on the forest ecosystem around them, the Québec government eliminated chemical herbicides on crown land back in 2001 (16). Forest management in Québec replaced herbicide spraying with strategies such as early reforestation, planting larger seedlings and applying more nutrients when needed, and mechanically removing unwanted vegetation (16). There have also been discussions in other provinces such as New Brunswick about whether to impose further restrictions on chemical spraying near dwellings, watersheds and protected areas (17).
When speaking of Ontario, Robin Horwath says, “We need to manage for the whole ecosystem. Whether it’s [for] trees, for reforestation, for climate change, whatever, but it’s also for the species that inhabit it.” And while this article has focussed on the effect of glyphosate sprayed in forest habitats, we have barely scratched the surface of the ample Indigenous Knowledge and published literature that is available on the effects that glyphosate has on the ecosystem at large. “We believe that glyphosate and the additives that enhance its potency are harming the health and well-being of the water, soil, birds, plants, fish, amphibians, invertebrates, humans and other mammals,” says the Traditional Ecological Knowledge Elders Group (1).
Ontarians are concerned about the environmental costs and misinformation about the safety of glyphosate-based herbicides due to the influence that Monsanto-funded papers have had on our discussions. Many feel that instead of spaying our forests with herbicides, the Ontario government should look towards protecting ecosystems through sustainable forestry management practices that are exemplified in Québec. Truly sustainable management practices will contribute to a stable economic recovery from the COVID-19 pandemic that benefits Ontarians and nature.
If you are concerned, consider taking a stand with many others who are speaking up against aerial spraying of herbicide in Ontario’s forests. Refer to the figure on the right or the resources below for ways that you can get involved in ending the use of glyphosate-based herbicides in our forests.
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Written by Olyvia Foster, Conservation Communications Specialist
Additional Resources – learn more/contribute to change
 The TEK (Traditional Ecological Knowledge) Elders of the North Shore of Lake Huron and Other Concerned Citizens. (n.d.). Position Paper. TEK Elders Group. Retrieved from http://tekelders.weebly.com/position-paper.html
 Connor, J.F., & McMillan, L.M. (1990). Winter utilization by moose of glyphosate-treated cutovers. Alces 26, 91-103.
 Florencia, M.F., Carolina, T., Enzo, B., & Leonardo, G. (2017). Effects of the herbicide glyphosate on non-target plant native species from Chaco forest (Argentina). Ecotoxicology and Environmental Safety, 144, 360-368.
 Edge, C.B., Brown, M.I., Hertz, S., Thompson, D., Ritter, L., & Ramadoss, M. (2021.) The persistence of glyphosate in vegetation one year after application. Forests, 12, 1-13.
 Health Canada Pest Management Regulatory Agency. (n.d.) National Aerial Pesticide Application Manual: Millennium Edition. (pp. Preface). Retrieved from https://www2.gnb.ca/content/dam/gnb/Departments/env/pdf/LandWaste-TerreDechets/Manuals-Manuels/NationalApplicationManualAerial.pdf
 White, E. (2019, July 19). Governments say glyphosate is safe, but some say ‘poison’ is being sprayed on northern forests. CBC News, Retrieved from https://www.cbc.ca/news/canada/sudbury/herbicide-spraying-glyphosate-roundup-northern-ontario-forests-1.5191978
 Arangio, S. (2021, January 23). ‘It’s a dead forest’:’ northern bush pilot, First Nations decry herbicide spraying. CTV News, Retrieved from https://northernontario.ctvnews.ca/it-s-a-dead-forest-northern-bush-pilot-first-nations-decry-herbicide-spraying-1.5279546?fbclid=IwAR2Vu7dNbcJvvaFUJ8rGAzN9jmaGik1vuSA7Hb7kw-M-G3Q5tfh3C-Sx4CQ
 Guiseppe, K.F.L., Drummond, F.A., Stubbs, C. & Woods, S. (2006). The use of glyphosate herbicides in managed forest ecosystems and their effects on non-target organisms with partial reference to ants as bioindicators. Maine Agricultural and Forest Experiment Station, Technical Bulletin 192.
 International Agency for Research on Cancer. (2016, March 1). Q & A on Glyphosate, World Health Organization, Retrieved from https://www.iarc.who.int/featured-news/media-centre-iarc-news-glyphosate/
 van Bruggen, A.H.C., Finchkh, M.R., He, M., Ritsema, C.J., Harkes, P., Knuth, D., & Geissen, V. (2021). Indirect effects of the herbicide glyphosate on plant, animal and human health through its effects on microbial communities. Frontiers in Environmental Science, 9:763917.
 Gillam, C. (2021, September 27). Glyphosate fact sheet: cancer and other concerns. US RTK, Retrieved from https://usrtk.org/pesticides/glyphosate-health-concerns/
[12 ] Shochat, G, & Fournier, S. (2019, March 12). Court documents reveal Monsanto’s efforts to fight glyphosate’s ‘severe stigma’. CBC News, Retrieved from https://www.cbc.ca/news/health/glyphosate-monsanto-intertek-studies-1.4902229
 Williams, G.M., et al. (2018) Corrigendum, Critical Reviews in Toxicology, 48(10) 893-894.
 Health Canada Pest Management Regulatory Agency. (2017, April 28). Re-evaluation decision: glyphosate. Health Canada, Retrieved from https://publications.gc.ca/collections/collection_2017/sc-hc/H113-28/H113-28-2017-1-eng.pdf
 Baum Hedlund Aristei & Goldman. (2021, August). Where is glyphosate banned? Baum Hedlund Aristei & Goldman, Retrieved from https://www.baumhedlundlaw.com/toxic-tort-law/monsanto-roundup-lawsuit/where-is-glyphosate-banned-/
 Thiffault, N., & Roy, V. (2010). Living without pesticides in Québec (Canada): historical context, current strategy, research, and challenges in forest vegetation management. European Journal of Forest Research, 130, 117-133.
 Ibrahim, H. (2021, November 3). Legislative committee calls for more glyphosate restrictions, Greens want full ban. CBC News, Retrieved from https://www.cbc.ca/news/canada/new-brunswick/glyphosate-herbicide-spraying-new-brunswick-1.6235387
 Botten, N., Wood, L.J., & Werner J.R. Glyphosate remains in forest plant tissues for a
decade or more. Forest Ecology and Management, 493, 119259.