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Invasive Plants and What They Can Teach Us About the Forces of Nature and Biodiversity. By Susan Leopold (Published in Plant Healers, fall 2012)

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By Susan Leopold

Invasive plants bring up many questions about how plants travel, how they take hold in various niches, how plants thrive and evolve and how they go extinct. This issue of invasives also begs the question as to what our role is at this moment, as the rate of extinction we are experiencing on a global scale is dramatically accelerated due to human activity. If you choose to fight invasive plants, you engage in battle that at times seems futile, but as you see intact habitat become more fragmented and native plants we love become rarer, then you can’t help but engage in these questions, and—as stewards of the wildlands—stand guard. For me personally, the loss of biodiversity and the rate of extinction could be no more severe in my presence than on my recent trip to Hawaii this past winter to research the logging of the last intact stand of endemic mountain sandalwood. United Plant Savers used existing data to map the historic range of sandalwood (Santalum paniculatum) and to then compare it to current populations we mapped, layered over data of habitat that had been completely taken over by invasive plants. This area is primarily the coastal zone since that is where foreign people have settled most intensively on the island. The native species have become a minority in their own habitat. The loss I felt that had transpired in just a few hundred years made my heart heavy with regret. How could our actions go so unaccounted for? I witnessed the result of native endemic flora found nowhere else in the world turned into cattle pasture, sugar cane, and military bombing terrain. Plants have little voice in this discussion, yet they continue to teach us about the forces of nature and our inherent connection to biodiversity. United Plant Savers has become increasingly aware of invasive plant issues and this past May UpS co-sponsored an invasive plant workshop in the foothills of Virginia.

The intention of this workshop was to present a holistic perspective and diversified approaches as to how one confronts the issue of invasive species. The morning discussion was a panel of various folks who spoke about the bigger picture and in the afternoon case studies were discussed in regards to the following species: Japanese stilt grass (Microsstegium vimineum), Garlic mustard (Alliaria petiolata), Autumn Olive (Elaeagnus umbellata), Tree of Heaven (Ailanthus altissima), and fescue (Festuca). What can be frustrating is that there are no easy answers and often the methods to deal with invasive are either very labor intensive or chemical warfare. In the case of Japanese stilt grass, a method of applying herbicides over a 5-year period each spring was one large-scale approach the state was using in a managed natural area, spraying along the roadsides and trails where the stilt grass had taken hold, finding its way by tires and by shoes that carry its seed. The thought is to be pro-active in this stage so that the stilt grass can be eradicated before it takes hold in the interior natural area. Hand pulling in the late summer before these annuals set their seed is what I do on my farm but it’s tedious, and I often feel that it has little effect. But I continue because I have witnessed the invasion in the woodlands near my home that were once carpeted with bloodroot and other spring ephemerals turn into a sea of wavy stilt grass.

In the case of garlic mustard, organized early spring pulling is an ongoing devotion but effective if pursued diligently. The nice thing about garlic mustard is that it can be eaten in the spring before your gardens are producing. This certainly brings up Timothy Lee Scott’s book Invasive Plant Medicine that presents how the invasives can be seen as messenger plants that bring us wisdom. I most certainly feel that being able to use invasives as medicine presents a radical opportunity as herbalists to connect the dots between what is happening to our health and what is taking place in our local environment. We are essentially the ultimate invaders, so it’s not surprising that some of these invading plants would provide necessary medicine, such as Kudzu in the south and Japanese knotweed’s healing virtues in regards to Lyme disease, discussed in detail in Scott’s book.

Aside from obvious herbicides and hand weeding, one very different perspective that was presented was ashing the seeds of the unwanted plant you wish to be gone. Hugh Courtney of the Josephine Porter Institute presented this concept. This ash can then be homeopathically diluted and turned into what Rudolf Steiner called a pepper spray. This is really fascinating to read about through the lectures of Rudolf Steiner, because the thought process is that the seed is the final culmination of the life force of the plant you wish to remove. Thus the ash of the seeds (the seeds passing through the fire) is then the opposite force that is developed in attracting the moon-forces. Applying this ash/pepper spray to your area of concern diminishes the forces of the moon that help the plant flourish. Steiner often spoke of the nature of things to be in cycles of four and recommends this treatment for four consecutive years to completely eradicate the species of concern. In Steiner’s time invasive plants were not an issue but weeds in the fields, insects in the garden, and field mice eating the stored grains were a problem. Thus his approach of using the biodynamic principles of gardening by the moon is thus reversed to remove those “weeds” or “pests”. Hugh Courtney’s presentation also included a case study of someone who was using the lectures of Steiner and the method of ashing to combat the Woolly Adelgid that kills Hemlocks in an effort to save an ancient grove in North Carolina.

In regards to Autumn Olive, a local goat farmer presented on the benefits of clearing his land of it and at the same time providing food for his goats. He also rented his goats to remove invasive plants from state and privately owned land. I myself have been using goats to clear land of invasive species as they most certainly are drawn to woody invasive that tend to take over abandoned fields. Often invasive plants are opportunistic, coming into areas that have been recently disturbed, but what about those species that are adaptable to grow in shade and invade a forest that has an intact healthy ecosystem? This is where I share a deep concern for the at-risk plants that UpS seeks to protect since many on the list find their home in the forest. Garlic Mustard and Japanese stilt grass are two invasive plants that have no problem invading the shaded forest and home of many native medicinals.

Dr. Anne Alerding presented her research that further helps to explain just how Garlic Mustard invades woodland forests. Garlic mustard is a biennial plant, so in its first year it emits a stronger dose of an allopathic toxin that then kills the fungi in the soil that are critical to native plants. In essence, by killing the fungi in the soil it then takes out the competition of the nearby native plants; then in its second year growth it can produce seed and start its cycle again. A deeper understanding of what is taking place lies in the dramatic decline in the leaf litter layer of the forest. Alerding’s research further demonstrates that in areas invaded by garlic mustard there are twice as many springtails, insects that are decomposers, and thus the increase in populations adversely affects the rate of decomposition, thereby decreasing essential soil nutrients for native plants. The link between the increase in springtails is attributable to the change in the ph of the soil, which becomes less acidic due to the die off of the soil fungi from the garlic mustard invasion. This research clarifies the complex relationship between plant invaders, soil chemistry, and decomposer abundance. This is quite the ripple effect for the takeover of woodland habitat, and it really stresses the importance of being pro-active in dealing with garlic mustard because the implications to the soil are that even if the garlic mustard is removed, it is unknown how the native plants might or might not recolonize the area. It goes beyond loss of native spring ephemerals, such as tooth wart also in the mustard family. The West Virginia white butterfly (Pieris virginiensis) in the caterpillar stage feeds on the tooth wart and is now at risk of extinction. as the eggs will not hatch due to toxicity of the garlic mustard.

The ripple effect of invasive plants, organisms, and animals is also apparent in the case of mountain sandalwood. Even if a moratorium on cutting sandalwood was put in place, the ecology of the habitat has been highly stressed due to fragmentation, coupled with invasive goats that devour sandalwood trees, pigs that destroy habitat, and rats that eat the seeds, thus the sandalwood trees are unable to reproduce, as the older trees die off. Sandalwood, as well as many other natives at risk will need our intervention if it is to continue to survive the many complex ecological pressures it is facing.

I agree with Jonathan Davies from McGill University when he states that “Reducing rates of extinction represents one of the greatest challenges of our time.” According to recent estimates, around 20 percent of flowering plants are currently at risk of extinction. There are many causes for the high rate of extinction that we are witnessing at this time. Most certainly there is the rapid population explosion of the human race that has taken place in the last 400 years, as we have multiplied from less than 1 billion to now beyond 7 billion people. This translates into loss of wildlands, an increase in the rate that invasive species travel to foreign lands, pollution, and development, all mostly caused by humans. Now we are seeing the effects on plants as they rapidly adapt to climate change, and the influx of exotic species.

Why is it important to understand more from a global perspective about how this rate of extinction impacts our lives? This is because species extinction could reduce productivity of plants on earth by HALF; plant productivity regulates the ability of nature to take greenhouse gases like carbon dioxide out of the atmosphere, as well as the ability of plant habitats to produce oxygen, food, fiber, biofuels, and medicine (Reich et al 2012). Researchers found that every additional species contributed to a gradual increase in both soil fertility and biomass production over a 14-year study period that monitored plots of agricultural land in the prairies of Minnesota. This is because diverse communities are more complementary in how they use biological resources. IN OTHER WORDS: different plant species play unique roles in the environment. This study that took place on the prairies in Minnesota demonstrates how diverse species have unique ways of acquiring water, nutrients, and carbon and maintaining them in the ecosystem. Essentially extinction equals loss of biodiversity, and an ecosystem with diminished biodiversity is one that is less productive, less functional in the services that we benefit from such as soil fertility, carbon sequestering, and the decline and potential loss of native medicinal plants. This is not good news for such a rapidly growing population that is dependent on fertile soils to grow essential food and filter water and intake carbon.

I end with such a larger picture of the issue so that when we narrow down to our own piece of heaven we can appreciate the deeper meaning of protecting and stewarding our regional native sanctuaries. United Plant Savers is concerned with the role of invasive species in protecting native habitats and the herbal plants we love that need these habitats to thrive. This is a different type of issue that concerns native medicinals unlike overharvesting; this is a threat that creeps up when we are not watching. It’s not so much about extinction as it is about grasping the importance of the biodiversity of our local native habitats. The lesson of invasive plants is also about being aware as to what these plants are trying to tell us. We need to be mindful of how we confront invasive plants in the most holistic perspective because the answers are few and the questions are many. We have to be asking the questions because being a steward entails the careful and responsible management of something entrusted to one's care, and for us it’s this amazing planet, inhabited by the diversity of flowering plants that we are deeply dependent on and to which we are deeply interconnected. Aldo Leopold, in Round River, stated it well, “One of the penalties of an ecological education is that one lives alone in a world of wounds. Much of the damage inflicted on the land is quite invisible to laymen.” This quote speaks well to the issue of native plants because many do not notice the loss of native habitat to invasive species, but, as conscious observers, we do need to be proactive in invasive plant removal to the best of our ability.


Reich et al., Impacts of Biodiversity Loss Escalate Through Time as Redundancy Fades, Science, 2012.

Plant invasion, soil pH, and epigeal springtails: implications for nutrient recycling in temperate forests. A.B. Alerding* and R.M Hunter. Department of Biology, Virginia Military Institute, Lexington, VA 24450 USA

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