As global temperatures continue to rise, scientists predict that environmental shifts will impact the ability of medicinal plants to grow and thrive in affected regions. Botanists across the world are shining light on the ways that climate change could fundamentally alter the practice of holistic medicine.
In January, a diverse group of plant experts spanning several continents issued a cautionary publication, entitled “Scientists' Warning on Climate Change and Medicinal Plants” (Applequist, W. et al. Planta Med. 2020; 86(1): 10-18).
The paper, published in the journal Planta Medica, outlines a myriad of detrimental effects that climate change could exert on certain medicinal plant species. Among them are potential decreases in availability––or in extreme cases, extinction––of key plant populations.
“The primary concern is that some valued species may either be unable to grow in some areas where they now live, or be subjected to increased environmental stresses that reduce their growth,” lead author Wendy Applequist, PhD, told Holistic Primary Care. Applequist has been studying plants for more than two decades, and currently serves as associate curator at the Missouri Botanical Garden’s William L. Brown Center in St. Louis, MO.
“Heat stress and drought are the two factors most likely to reduce productivity,” she explained.
The specific risks to individual species, however, vary significantly by region and by plant type. Researchers are still working to determine the areas in which climate-related plant dangers are the greatest.
“Not enough is understood about this issue yet, but the species most at risk are predicted to be those living in areas that will undergo the most rapid climate change,” Applequist proposed. At-risk species include those living in high mountain territories, polar regions, and arid zones or areas that could become much drier as weather patterns continue to fluctuate.
Applequist's group highlights the fact that thousands of medicinal plant species provide countless human health benefits to communities around the world––especially in areas where conventional Western medicine is unavailable.
“Medicinal plants are an important component of health care for most of the worldʼs population: they constitute the primary materia medica for 70 to 95% of citizens of most developing countries,” the group writes.
Demand is also on the rise in the developed world, as plant medicines are “increasingly utilized by large numbers of people residing in wealthier countries,” they add. Were climate change to broadly disrupt the medicinal plant kingdom, its impacts would be felt worldwide.
Plants rely on environmental cues such as changes in temperature or moisture to signal the start of seasonal activities like bud and leaf production. But if flowers bloom before their pollinators are active, or if fruits fail to ripen until after birds and other seed dispersers have already migrated to distant areas, plant reproduction cannot occur as it normally would.
Outside the US, and even in certain regions of this country, medicinal plant species fill a gap where conventional treatments are unaffordable or inaccessible. If changes in climate compromised their ability to acquire to safe botanical products, individuals in vulnerable areas “would suffer harm from reduced or lost access to effective and affordable medicinal plants.”
Still others could lose access to important native plant medicines in areas where environmental change threatens to displace communities from their traditional homelands as climate refugees.
Two popular plants under threat include American ginseng (Panax quinquefolius) and Goldenseal (Hydrastis canadensis), both native to the United States with long histories of medicinal use.
“American ginseng is being completely obliterated from large portions of its range, and goldenseal is endangered and in decline in many areas,” Applequist said. “These are examples of the kind of plant at greatest risk: slow-growing small perennials that are commonly wild-collected and for which harvest usually destroys the plant.”
Plants that preferentially grow at very low altitudes in coastal regions like southern Florida are also at risk, since “most will find it difficult to grow when they are covered with a couple meters of salt water,” she added.
“American ginseng is being completely obliterated from large portions of its range, and goldenseal is endangered and in decline in many areas”--Wendy Applequist, Curator, Missouri Botanical Gardens
In other areas, frequent droughts, wildfires, and extreme weather events endanger plant and human populations alike. Continued warming could also increase the ranges of both plant diseases and insect pests, further threatening plant growth and health.
Another recent report in the American Botanical Council’s quarterly HerbalGram journal warned that climate change could also damage crucial relationships between plants and their pollinators, a phenomenon known as “phenological mismatch.”
Plants rely on environmental cues such as changes in temperature or moisture to signal the start of seasonal activities like bud and leaf production. But if flowers bloom before their pollinators are active, or if fruits fail to ripen until after birds and other seed dispersers have already migrated to distant areas, plant reproduction cannot occur as it normally would. That can generate competition among plant populations for critical resources, creating conditions that tend to favor invasive species over native plants (Bauman, H et al. HerbalGram. 2019; 124: 44-61).
Plant-pollinator imbalances also “impact the timing of when plants are ready for harvest, which disrupts harvesting practices,” added Ann Armbrecht, PhD, Director of the Sustainable Herbs Program at the American Botanical Council.
Apart from disrupted growth and reproduction, climate change may impact the quality or safety of some medicinal plants.
Environmental stressors can trigger changes in a plant’s phytochemical content, potentially affecting its pharmaceutical properties. In some cases, that might spell danger––but in others, it could actually be beneficial.
Depending on a plant’s unique phytochemical profile, increases in certain plant compounds could either boost the plant’s medicinal power, or contribute to its toxic or noxious side effects.
“It is not uncommon for plants that are under particular stress to show increased chemical potency––either they are producing more defensive compounds, or they are not growing as well, so the concentration per gram of plant tissue is higher,” Applequist said.
She stressed, however, that most climate-induced quality concerns are largely hypothetical at this point.
“There’s really not enough information yet to know how climate change will affect plant quality,” she noted. Defining the potentially negative consequences depends upon what characteristics one is looking for in a particular plant, and whether not it retains its capacity to meet the therapeutic needs of its users.
“If we define quality as high concentration of active metabolites––which a traditional healer might not do––then some plants, in some places, will likely increase in ‘quality’ because they are stressed and don’t grow as well,” Applequist argued.
It is not yet clear precisely how regional environmental changes will impact each individual plant species. “Conservationists can predict, from seeing where a plant lives today, whether it will still be happy in a certain place fifty years from now,” she explained. Some species are unlikely to be affected by climate change, and others may even thrive under warmer conditions, “just as I find 70° in January much more congenial than 20°, however abnormal the former is,” she said.
But for most species, botanists have not yet completed the time-consuming work of projecting a plant's future viability under changing conditions.
In the US, most commercially available herbal supplements are made with very safe botanicals with a broad therapeutic dose range. “If your Echinacea or St. John’s wort unexpectedly became 10% or 20% more potent, it wouldn’t hurt you,” Applequist said.
"Plants that are really poisonous if misused are hardly ever used, and never in commercial products. People aren’t using species like Senecio that contain toxic pyrrolizidine alkaloids, or even Foxglove, for which careful dosing to avoid digoxin toxicity used to be essential.”
Despite the many remaining unknowns, Applequist and her co-authors nevertheless called attention to hypothetical safety issues because “there are still many places where professional practitioners use plants with a narrow therapeutic dose range.” Chemical testing would be needed in such cases to identify any changes in the levels of vital plant compounds and determine appropriate dosage adjustments.
Far more tangible are the ways that climate change is exacerbating the existing pressures on many plant species. Factors like rapidly expanding global consumer markets, overharvesting, and human-induced habitat fragmentation pose “perennial threats” to numerous plants, even without the added burden of mounting environmental stress.
“More than a few species are already being unsustainably harvested,” causing declines in wild plant populations, Applequist said. “If they take another, separate hit from climate change, the combination could be enough to wipe out many populations.”
In general, “if a botanical can be cultivated without its quality diminishing significantly, that’s more sustainable than wildcrafting it from declining natural habitats."
The source material for most certified organic botanical products is cultivated, not wild-crafted, as growers must adhere to the USDA's stringent National Organic Program growing guidelines in order to obtain certification. There are, however, some wild-harvested products that do meet certified organic requirements.
Anything that diminishes populations of medicinal plants––whether wild or cultivated––will increase the risk of intentional adulteration or substitution. It's simply a matter of supply and demand. When demand is high, but supply is low, suppliers have strong incentive to cut, alter, spike, or fraudulently misrepresent the herbs that they're selling.
Adulteration is widely recognized by everyone involved in herbal medicine as a major issue, and one that will only be made worse by any climate-related downturns in availabiltiy of popular herbs.
According to Mark Blumenthal, executive director of the American Botanical Council (ABC), between 35% to 40% of the herbs in the most popular botanical medicine products are potentially subject to intentional adulteration. Among them are Goldenseal (Hydrastis canadensis), Saw Palmetto (Serenoa repens), Bilberry (Vaccinium myrtillis) and Black Cohosh (Actea/Cimifuga racemosa).
This does not mean that all these herbs are always adulterated, but the risk is there.
Several years ago, ABC launched a comprehensive Botanical Adulterants Prevention Program (BAPP), to identify poor quality adulterated herbs, and ideally, eliminate them from the supply chain.
Last year, ABC joined forces with the American Herbal Pharmacopeia, and the National Center for Natural Products Research at the University of Missisippi, to launch a campaign called "Burn It, Don't Return It." The program's goal is to encourage supplement makers to rigorously test all herbal raw materials, and to destroy––at the cost of the materials supplier––any shipments that are proven to contain adulterants, additives, contaminants, or substituted plants.
"Burn It" has won broad support from herbal medicine companies and from the dietary supplement industry as a whole. Hopefully, over time, it will mitigate the problem of economically motivated raw materials adulteration.
Protecting the Plant World
Applequist and her colleagues recommend a number of actions to support important botanical species; these include preservation of traditional plant knowledge, broadening the local cultivation of valued plants, conducting sustainability training for harvesters, obtaining certifications for commercial materials, and establishing programs to monitor raw material quality.
When it comes to choosing safe dietary supplements, she says there are two ways: “The old-fashioned way is to get it from a real herbalist who makes an artisanal product starting from raw materials. It won’t have all the chemical testing...demanded by the current federal GMPs [Good Manufacturing Practices regulations], but has no need [for] it,” she said.
The second option is to purchase products from a corporate manufacturer that “takes seriously the need to control their supply chain by using traceable ingredients whose source and quality they have investigated.”
Avoid supplement makers that “just buy processed material (powders or extracts) at the cheapest available price, on the happy assumption that one barrel of ‘black cohosh’ is as good as every other barrel.”
While some institutions do offer certification programs relating to product sustainability, it is “hard to be sure whether such a certification is really rigorous or just greenwashing.” As always, it is essential that clinicians who prescribe dietary supplements do their own research to identify trustworthy, responsible brands.
ABC's Ann Armbrecht similarly encourages medical professionals to “do what they can to support plants and the habitats in which they grow.”
“Think about the whole ecosystem and how to help that be healthier. In the end, it doesn’t matter what supplements anyone takes if the environments in which we live are not healthy.”
Medical practitioners can “choose to only purchase wild-collected plants that have been certified, or if those aren’t available, encourage companies to develop certified sources of wild-collected plants,” she proposed. “They can support large-scale conservation programs and habitat protection. Clinicians can also encourage or support research to monitor biomarker content, especially in alpine species, to identify potential changes in potency,” she added.
At this point, the evidence that climate change is causing real ecological harm across the planet is overwhelming. The question confronting us now is whether or not we listen to scientists’ urgent warning calls.
“There is a lot that isn’t known” about the long-term impact of global warming, Armbrecht noted.
“But it seems, as we all watch the coronavirus (COVID-19) spread around the world and bring [it] to a standstill––something that epidemiologists have been predicting would happen––it would behoove us to pay attention to these indicators and signs before it is too late.”