It seems almost quaint, or perhaps naïve, to imagine a time, not too too long ago, when black and white film strips proclaimed the wonders of chemistry and suburban children danced gleefully behind fumigators in fluffy, white clouds of pesticide. We live in a more skeptical time today, and for many people, the word pesticide is more likely to evoke images of malformed frogs, Agent Orange, and GMO seeds than it is anything positive.
Among chemical herbicides, glyphosate, the active ingredient in Roundup, may be the most scrutinized. Its use is bitterly debated in agricultural circles, and this bleeds over into forestry and into the pages of this magazine. Chances are you know someone who’s using glyphosate in their forest management activities (if you’re not using it yourself), be it for controlling invasive plants in southern Connecticut or regenerating spruce in a clearcut in northern Maine. Highway departments, fisheries managers, homeowners, conservation groups, are all using the chemical on a regular basis. And chances are that unless you have degrees in biochemistry and toxicology, you really don’t know what to make of it. How can we reconcile the glyphosate in our sprayers with the copies of Silent Spring on our bookshelves? How can we trust something we don’t understand?
What is it? Is it harmful?
The first step to try to make sense of glyphosate, and herbicides in general, is to figure out what they are and what they do. And the more you talk to smart people who do understand chemistry, the more you hear that, generally speaking, the toxicity of most herbicides to animals is low. This makes a certain amount of sense, because animals aren’t plants. Plants are autotrophic organisms, which means they manufacture their own nutrients from the water, minerals, and light they take in from the environment. Humans are heterotrophic, which means we don’t manufacture our own nutrients – we consume them by eating plants and animals.
Glyphosate kills plants – and this is the clinical version – by interfering with the synthesis of the amino acids phenylalanine, tyrosine, and tryptophan. It does this by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which catalyzes the reaction of shikimate-3-phosphate (S3P) and phosphoenolpyruvate to form 5-enolpyruvyl-shikimate-3- phosphate (ESP).
In nontechnical terms, what’s happening is that the glyphosate molecule is blocking a plant enzyme that produces amino acids and, as we all remember from high school science class, amino acids are the building blocks of life. This disruption occurs in what’s known as the “shikimate pathway,” a biosynthetic pathway that is specific to plants and some microorganisms. Since humans don’t have a shikimate pathway, we don’t have to worry about the glyphosate translocating to our growing points and making us wilt any more than a plant has to worry about contracting West Nile virus from a mosquito.
But just because we don’t have the same physiology as a plant doesn’t mean that Roundup (or any of the other 750 U.S. products that contain glyphosate) is necessarily benign in humans or other mammals. And here’s where things get murky and controversial, because while glyphosate is the active ingredient in a glyphosate-based herbicide, it’s not the only chemical. And while Roundup is the most common trade name for glyphosate, there are lots of different glyphosate-based herbicides made with different ingredients by different companies. The chemical company Monsanto introduced glyphosate to the world in 1974, but its patent expired in 2000.
Glyphosate has been subjected to hundreds of tests over the past 40 years, and the results are voluminous, though opponents of pesticides point out that most of the data come from research that is funded by the agricultural chemicals industry, and is thus junk science, while supporters say that it’s the politically motivated science coming from the anticorporate activists that is, in fact, junk.
Dr. Keith Solomon, director of the Centre for Toxicology at the University of Guelph and co-author of the book Pesticides and the Environment, points out that this testing framework may be controversial, but it is practical and not without precedent. “The idea here is that the companies who make the profits – not the taxpayers – should be paying to test the products,” said Solomon. “This is the same framework that’s used in pharmaceutical testing because it provides a dependable funding source for the testing.”
According to EPA spokespeople, “the burden of generating the data to support a pesticide registration rests with the company requesting the registration . . . and the research is conducted and evaluated in accordance with a series of internationally harmonized and scientifically peer-reviewed study protocols.” The tests are carried out in-house, in contract laboratories, or at universities. After registration, scientists continue to research the chemical independently in universities and federal labs. There’s an additional layer of protection in the fact that most developed countries have their own EPAs that independently examine the available pesticide data.
When asked how people can trust that the science is good, Solomon pointed out that the standards for good laboratory practices, promulgated into statutory law back in the early 1980s, require that every bit of data collected by a company doing research to support registration of a pesticide or pharmaceutical be subjected to audits by regulators such as the EPA. “As long as the research is conducted under the guidelines of good laboratory practice and has quality control, it’s good,” said Solomon. “Of course some people may go on to interpret the results in different ways, just as they interpret the Bible in many ways.”
Researchers at Cornell, among other major universities, analyzed toxicology tests in 1996 and concluded that glyphosate is “practically nontoxic” by ingestion, and it’s unlikely that the chemical would produce reproductive, teratogenic (birth defects), mutagenic, or carcinogenic effects in humans (read the results yourself). But because science is never 100 percent certain about anything, you can see where phrases like “practically nontoxic” leave an opening for attack. The web is awash with antiglyphosate stories with headlines like: 50 percent of rats given this died – Why is it on your dinner plate? And, indeed, if you fed rats more than 5,600 mg/kg of the chemical they would probably die. (To put this number into perspective, a proportional dose for a 150-pound human would be 840 g, almost two pounds; table salt would kill you at 350 g.) But by making an extreme example the rule, and overlooking the fact that rats fed 400 mg/kg a day for most of their lives showed no adverse effects, such stories give readers a skewed picture of the real-world health risks.
While the bulk of the scientific literature indicates that glyphosate in reasonable doses is nontoxic to animals, Roundup and other glyphosate-based herbicides contain adjuvants (chemical agents that are added to the glyphosate to increase its effectiveness) and surfactants (foaming agents that allow the liquid to bond to and penetrate a leaf) that are not necessarily benign.
“Roundup presents an unusual situation because the active ingredient (glyphosate) is nontoxic to animals, but the surfactants can be toxic, especially to aquatic organisms,” said Solomon. These surfactants are similar to those used in common household products and cleaners, and they’re controversial because the manufacturers do not have to disclose them for proprietary reasons.
The surfactant POEA (polyethoxylated tallowamine, a chemical derived from animal fat) seems to be the most scrutinized “inert” ingredient in Roundup. It’s essentially soap (your shampoo contains surfactants), and because soap dissolves fat and cell membranes are made of fat, aquatic animals such as fish and frogs are sensitive to it (as are eyes, which you’ll know if you’ve ever been careless with your spray-bottle of Roundup – or shampoo). There are glyphosate based products that don’t contain POEA and are designed specifically to be used in aquatic ecosystems.
Recent POEA-related headlines bear out Solomon’s earlier Bible reference. In 2009, French scientists exposed human cells to Roundup and found that cell membranes of embryonic, placental, and umbilical cord cells can be damaged by the surfactant. The finding is controversial, though, because a human being is a more complex organism than a handful of cells sitting in the bottom of a petri dish. And because our skin protects the inner parts of the body, the surfactant would not reach your more vulnerable cells, which also wouldn’t survive floating in dish soap.
There’s so much noise surrounding glyphosate and its surfactants that it’s difficult to report on any of it objectively, though I think it’s fair to say that the old adage “the dose makes the poison” applies here. I asked a number of toxicologists why people seem to have an easy time evaluating some potentially harmful things from an analytical, risk/reward perspective (bacon consumption, say, or excess exposure to the sun), but have such a hard time looking at chemicals in the same way. Some blamed the media, saying that people have been trained to respond negatively to fear-words like pesticide. Others took a more philosophical bent, and said that people have an easy time rationalizing risk they inflict on themselves (bacon for breakfast) but feel affronted by risk that they feel is being inflicted on them by someone else (the Roundup being used to fight invasive plants in the park).
Ultimately, it’s up to the EPA to decide how to interpret the science and render a decision on the safety of a chemical. The last mandated review began in 1986 and ended in 1993, at which time glyphosate was placed in Toxicity Category III and deemed safe enough to be sold over the counter. (Chemicals in Toxicity Category I have the highest degree of toxicity and those in Category IV the lowest.)
The EPA is currently reexamining glyphosate, a process that began in 2009. Beyond the “registrant generated data” provided by the chemical companies, the EPA will be evaluating information from independent testing labs, open scientific literature, and information submitted by the public, so they will be considering studies like the aforementioned umbilical cord trial as they make their determinations. The agency says it wants all the relevant data gathered by September 2012, and expects to issue a glyphosate decision for comment in 2014 and a final decision by 2015. At that time they’ll either restrict its use or continue to approve the chemical with no changes.
Glyphosate use in the industrial forest
The passion that’s fueling the glyphosate debate goes beyond the question of the chemical’s toxicity, and much of the fervor comes from the world of crop agriculture. Roundup-Ready seeds (seeds of plants that have been genetically modified to resist glyphosate, so farmers can plant, spray their fields with the herbicide, and the weeds will die but the crops won’t) are controversial, and they open up a whole different line of discussion about the ethics of creating herbicide-resistant weeds, making third-world farmers depend on chemical companies for seed, and clashing with organic farmers over cross pollination.
Glyphosate’s use in forest management is somewhat less controversial, because it’s not being applied to a food crop, and it’s not being used repetitively at high rates. (Farmers apply it every year; foresters apply it once every 50 years.) It’s hard to tease out exact numbers, but research suggests that approximately 1 or 2 percent of total glyphosate use in the U.S. is in forests; according to the most current EPA data available, about 200 million pounds of the chemical was used in the U.S. in 2007.
But this isn’t to say the chemical’s not controversial in the woods.
The debate surrounding glyphosate use in plantation-style forestry mimics the debate over glyphosate use in traditional crop agriculture because, like industrial farming, industrial forestry is all about efficiency. In the northern forest, where large companies manage huge acreages to feed the global wood products market, glyphosate is commonly used to help regenerate stands of softwood. Clearcuts are made in fall or winter. Once the vegetation starts to regenerate, the chemical may be applied from an airplane or helicopter, usually in the late summer. The application will kill or suppress the hardwood seedlings, shrubs, grasses, and forbs that would otherwise outcompete the conifer seedlings. The conifers are left unharmed, because in late summer their needles develop a thick, waxy covering (called a cuticle) that keeps the herbicide from being absorbed.
The results of this method of management are significant. In one long-term study, wood volume yield increased by 477 percent in test blocks that were treated with glyphosate. A separate study found that the cost of a cubic meter of wood tripled when conifers were released by workers with brush saws, rather than by the aerial application of herbicide.
“In general, foresters, like farmers, would prefer not to use herbicides,” said Dr. Bob Wagner, Director of the School of Forest Resources at the University of Maine. “Herbicides are expensive, difficult to apply, and much of the public opposes their use. Foresters generally use herbicides when there is no other economically viable or effective way to meet legal reforestation requirements, meet landowner objectives, or meet the objectives of sustainable forest certification.”
Wagner has been studying glyphosate use for 30 years. He came to the field as a forestry student opposed to herbicides, but soon after working for a research program looking for alternatives to herbicides, he began to more fully appreciate the complexities involved. “Herbicides are a tool,” said Wagner, “just like fire, animals, and machines. And just like any tool, they need to be selected based on many advantages and disadvantages.”
A distinct disadvantage would be indirect effects on wildlife, and researchers at UMaine synthesized this data in a lengthy report that’s available online here.
The bulk of the research suggested that in the short term (1–3 years), clearcutting and subsequent glyphosate application at recommended rates had an indirect effect on small mammals, large herbivores, songbirds, invertebrates, and soil microorganisms; the chemical didn’t affect these organisms, but changes to the ecosystem brought about by the clearcut and the subsequent removal of the vegetation did, as you’d expect with any ecosystem disturbance regardless of the methods used. After about five years, treated stands were either back to normal or more diverse than before the treatment. Several laboratory and field simulation tests clearly demonstrate that amphibian species are vulnerable to formulated glyphosate products containing certain surfactants, but multiple field studies showed that applications made at recommended rates in forest settings did not produce any mortality or significant toxic effects.
Dean Thompson, a research scientist with the Canadian Forest Service, says that after a comprehensive review of the scientific literature he’s seen “no indication of acute toxicity effects to amphibians under realworld scenarios when glyphosate-based herbicides are used in accordance with their specific product labels.”
When asked about persistence in an ecosystem, Thompson said that glyphosate is “moderately persistent” in forest soils and that the longevity depends on a wide variety of site factors including temperature, moisture, microbial activity, and the type of soil involved. In one detailed study conducted in New Brunswick, Thompson and co-workers observed the time required for glyphosate to dissipate by 50 percent to be in the order of 10–12 days, while review of a number of studies conducted in a wide variety of forest sites across North America suggest estimates ranging from 10-60 days.
Asked about off-site movement, Thompson said, “Glyphosate binds strongly to soil particles, and as a result of that, it has an exceedingly low potential to move into ground water in natural forest ecosystems.” However, there are scenarios where following torrential rains, the glyphosate that’s attached to soil particles could be carried with such particles into streams, rivers, or other surface waters.
Every forest disturbance – from a footfall to a treefall to an herbicide application – has an effect on an ecosystem, and there is debate about potential harm to an ecosystem if the herbicide is misapplied (or whether the body of research is adequate to make any definitive declarations). What’s really interesting, though, is that unlike glyphosate use in conventional farming, where such charges bounce like paper arrows off big agriculture’s government-supported mandate to feed the world, herbicide use in industrial forestry is decreasing across our readership area. And it’s not because chemical opponents have made the case that the herbicide is unacceptably harmful. It’s because of widespread objections to clearcutting.
The Ecology Action Centre, an environmental organization that opposes large clearcuts and plantation-style forestry in Nova Scotia, recently released a report that sums up their perspective like this:
“While glyphosate may have negligible effects on wildlife, glyphosate has been an integral component of plantation silviculture. As such, glyphosate helps alter natural plant communities and successional trajectories, shifting the Acadian forest to a less structurally diverse environment and, as such, a less stable environment.”
Foresters can argue passionately about the validity of the last clause in that quote, but it adequately sums up the ecological mandate in parts of Canada.
Following a public hearing process, chemical herbicides were banned on Crown forest lands in Québec in 2001. (Crown lands constitute about 90 percent of the provincial forest land base.) Today, these forests are being managed under an ecosystem-based management philosophy that seeks to take advantage of natural succession patterns rather than clearcutting and planting.
This has been a challenge in a region where 16 percent of manufacturing jobs are related to timber and pulp production. There are studies that show desirable regeneration has dropped off significantly in certain areas, and there’s concern over how this will affect long-term forest productivity. One report from Nova Scotia showed that 87 percent of conifer plantations failed outright when herbicide use was discontinued. However, other studies show that chemical-free forest management strategies are working well in certain areas and by certain metrics. One study reports an increase in understory plant diversity that didn’t exist in a chemically-treated clearcut. Another reports that intense mechanical scarification and the resulting diversity of pin cherry and willow trees in a softwood plantation was improving soil structure in a way that clearcutting and chemical control never could.
While there are strong opinions on either side of this debate in Canada, in 2008 the Québec government reaffirmed its commitment to ecosystem-based management of public forests. (The flip side of this coin is that the province of Alberta suspended their herbicide program in the late 1980s and by the early 2000s had such large regeneration failures that they reinstated the program.)
This trend against clearcutting and glyphosate use in Québec reflects what’s going on in Maine, too, where public outcry against clearcutting resulted in the forest practices act in 1989. In the wake of the spruce budworm epidemic in the early 1980s, 80,000 to 100,000 acres were being clearcut a year. Today, about 15,000 acres, less than 3 percent of the annual harvested area in the state, is clearcut. Wagner says that glyphosate application is down substantially as a result of this change in harvest practices, as is the forest herbicide research being conducted in the university system.
Glyphosate in hardwoods
Foresters in Maine, Vermont, and Pennsylvania whom I spoke to all agreed that glyphosate use in hardwood management has probably increased over the past 20 years, though it should be noted that glyphosate is not the only herbicide being used.
In many parts of the Northeast, dense stands of diseased beech have become a hindrance to hardwood sawlog production. Glyphosate is a very effective tool to use against beech, since you can drill a hole in a beech stump, add a capsule or dollop of the chemical, and count on it to spread to all of the root sprouts that have grown from the parent tree.
Foresters cite the fact that herbicide kills a plant’s roots as a key selling point. Trees don’t, as a general rule, die when you cut them, which means that with a manual control regime you often have to come back over and over again to kill the stump sprouts and suckers. (Editor’s Note: If you want to learn more about glyphosate use as it relates to hardwood management, check out the story Got Fern? in our Autumn 2010 issue.)
Guy Dunkle, a forester who manages more than 7,000 acres for Firth Maple in Spartansburg, Pennsylvania, says that in his area, herbicide is used on a large scale with tractor-mounted mist blowers. “This is the nuclear option,” said Dunkle, “used in areas with big problems.” But in many situations, glyphosate is applied more selectively.
“We use cut-stump applications where we’re controlling beech brush,” said Dunkle. “We spray a 50 percent solution of glyphosate and water immediately after the tres are cut. There’s no overspray, and one shot kills eight or ten trees. In areas where we’re treating trees that don’t root-sprout, we’ll use a small cordless drill to tap the trees like you would a maple for syrup production, then add glyphosate into the hole.”
Glyphosate in invasive management
In cords and boards forestry, “management” often means steering forest succession toward a desired mix of economically valuable species. But as our increasingly globalized world leads to a greater presence of exotic invasives in the forest, environmentalists – many of whom own both dog-eared copies of Silent Spring and backpack sprayers – are finding the chemical useful in the war against invasive exotic plants that are fundamentally altering native ecosystems.
Sharon Plumb, invasive species coordinator for the Vermont chapter of The Nature Conservancy (not exactly a group you’d associate with Dow-Chemical) speaks for a lot of reluctant glyphosate users when she says, “It’s an issue I’m really conflicted about.”
“I don’t agree with using glyphosate for growing food,” said Plumb. “I am a big advocate for mechanical treatment if it can work. But there are certainly cases where judicious herbicide usage is the lesser of two evils, especially when the alternative is to let invasive plants take over an ecosystem unchecked.”
Plumb uses the knotweed in her own backyard as an example.
“It’s difficult to kill knotweed by digging because of the root fragments that stay behind,” she said. “So to manually treat it, you need to hand-cut the plants, then come back every month during that entire first growing season to knock back the regrowth, then come back at least once a year for five years and repeat. That is how I got rid of the knotweed in my own backyard, but it’s just not possible to do this on a large scale.”
Plumb says that, when possible, The Nature Conservancy will mechanically treat knotweed. But on large properties and big problems, they’ll use a combination of hand cutting and glyphosate application. “We’ll do a round of hand cutting, then we’ll come back when the plant is short and wimpy and hit it with foliar spray. This allows us to minimize our herbicide use.”
In forest settings, The Nature Conservancy has treated barberry infestations that stretched on for dozens of acres and had come to completely dominate the native ephemerals, shrubs, and seedlings. In such examples, Plumb says, “The future of that forest is very much at stake. Propane and grazing could be options for large infestations, depending on the situation, but if you chose to treat with herbicide, within a year you could knock that infestation back and allow for that forest to return to a more healthy, natural state. You can then be diligent about keeping an eye on future infestations and hand-dig those plants early.”
Talk to people who use the chemical in the invasive-exotic field, and you’ll find that many of them see invasive species as a cancer on the land and glyphosate as the chemotherapy. You wouldn’t casually dose your woods with it any more than you’d casually bombard your body with radiation. But if the ecosystem’s sick – what choice do you have?
So where does all this leave us – the people without advanced degrees in biochemistry or forestry who are looking at the forest problems on the back 40 and going back and forth about the bottle of Roundup at the local hardware store.
To some of us, laboratory-manufactured chemicals like glyphosate will never be acceptable. And there are many nonchemical alternatives that the small woodlot owner can use to steer forest succession on their woodlots. (Editor’s Note: See Brett Chedzoy’s silvopasturing essay on page 16 for just one example.)
To others, glyphosate is a safe and useful tool that’s fundamentally no different than a chainsaw. Advocates for herbicide use will argue that if they’re to manage a forest proactively – for timber, for wildlife, for ecological integrity – they need a full tool box. If herbicide’s a hammer, asking them to manage certain parcels of land without chemicals is like asking them to drive nails with a screwdriver. It may be possible, but it’s inefficient and costly.
Defining the poles makes it seem like we haven’t really progressed in our environmental consciousness since the 1970s, when pesticides were either a magic bullet or an ecological disaster. But most people’s views on the chemical fall somewhere in the middle. And every forester I spoke to for this piece indicated that the use of herbicide in silviculture has evolved over the past 50 years, and is becoming more targeted and fine-tuned.
I asked Rob Bryan, an ecological consultant and Forest Stewardship Council (FSC) certifier from Maine, if herbicide use is allowed under FSC (it is), and as he walked me through the thought process an FSC auditor uses when approving an herbicide, it struck me as good common sense.
“First, I see if a landowner has done an analysis to justify herbicide use versus another approach,” said Bryan. “The test is if there’s not an alternative approach, or if the alternative is prohibitively expensive, or if herbicide is the only effective means, or if the herbicide use will create less environmental damage than nonchemical treatment – a place with sensitive soils, for instance, where mechanical treatment would do more harm than good. If the landowner can show that there are no feasible or less damaging alternatives, then I check to see if they’ve selected chemicals and application methods that minimize risk to nontarget species and sites – for example, aerial spraying versus backpack versus cut-stump. Finally, the landowners need to ask themselves whether the forest can be managed in such a way that herbicide use can be reduced or eliminated over the long term.”
If you’re looking for the middle ground that acknowledges both the risks and benefits of the chemical, that might be it.
Dave Mance III is the editor of Northern Woodlands.