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Ecologically Managing Invasive Species Part 1: Problem or Symptom?

Updated: May 1

As a farmer, I spend a lot of time growing and tending to plants, with annual crops requiring the most time and energy. Each year, I add a few additional perennials that once established will grow with only periodic attention from me. I’m also interested in identifying and using plants that are already established around the farm, including introduced or non-native “invasive” plant species. I prefer to think of these as opportunistic or pioneer species. I’ve also heard them called band-aid or persistent species as well as joyful growers. I use these various terms interchangeably.

Nigerian dwarf goats eating autumn olive berries as part of our strategy to ecologically manage invasive plant species

The term “invasive” and even “weed” is relative and primarily indicates a plant growing where we don’t want it. The term “native” is also relative since ecosystems are constantly evolving and plant species come and go over time – something that climate change will accelerate. Every plant had to “invade” a new area to become established so I avoid labeling plants as either good or bad.

In Part 1, I discuss my evolving thoughts on to appr"invasive" plants, including ways I try to ecologically manage these opportunistic species. My views on this topic were shifted in part by my own observations and experiences but also through the help of a couple thought provoking books. There are likely other good books available but our local library had these and they were interesting to read:

Beyond the War on Invasive Species by Tao Orion

Where do Camels Belong? Why All Invasive Species Aren’t All Bad by Ken Thompson

In Part 2, I provide specific management strategies for the introduced species we have on the farm and how I’m trying to utilize these plants as a resource rather than view them solely as a problem. At a minimum, I’m working to understand the role(s) these hardy plants may be playing in filling gaps created by disturbance and/or past land uses.

From Enemy to Ally

The native vs. non-native debate can be a heated topic. However, as we face a changed and changing climate that will be even less stable in the future, we need to be open-minded and educate ourselves about unfamiliar plants. Some of these plants may be better suited for our future climate than the plants we currently think of as native. Plants adopt a variety of traits that allow them to interact differently with the environment. Not all introduced plant species become “invasive” but many of the changes already threatening native species may end up giving introduced species a competitive advantage. With this understanding, we should think about the spread and/or establishment of introduced plants as an effect rather than a cause thanks to the various human-caused changes.

We certainly need to better understand how introduced plants grow and propagate to avoid problematic species. Yet the line is often blurred when it comes to the non-natives we welcome (such as apple trees and lilacs) and plants we label as threatening. Often it is only after a new arrival has become established that we may realize our concerns were overblown or identify benefits these plants have been providing. Example benefits include cleaning up pollutants or excess nutrients – something many opportunistic plants are good at (such as purple loosestrife), whereas many natives can become stressed and decline with increasing pollutants. If we solely view these plants as “bad” and focus only on their perceived negative traits, we may never allow ourselves to notice their positive ones.

For many years, I focused primarily on eliminating the most prevalent “invasives” growing in our area. I have since shifted to first learning about their benefits, growing conditions, and other natural means of reducing their competitive advantage before I jump in to remove or suppress them. Each plant is managed differently based on where it is growing (i.e., edge habitat, pasture land converting back to forest, recently disturbed land). I do my best to seek out productive uses of these plants that keep their growth or spread in check, thus giving the surrounding vegetation an advantage. Whenever possible, I also look for ways to enlist the help of our local deer population. Buckthorn and autumn olive are two such plants that deer already eat and are happy to keep pruned. In areas that I want their growth suppressed or the plants eventually removed, I simply cut taller plants down to browsing height. Deer prefer to snack on new growth and help control this regrowth.

Ecological control of buckthorn plants by cutting them down to allow deer to browse new growth
Buckthorn stumps cut down to deer browsing height

Humans have always moved plants and are responsible for regularly introducing new species as well as creating conditions that tend to favor hardy pioneer species. To minimize future unwise introductions, it is therefore important to research and understand a plants’ ability to escape the garden or yard and become established elsewhere. Plants in the mint family are an example of joyful growers that will happily spread if allowed. Ideally we should first look around to see what is already growing and work to mimic the existing plant community – keeping in mind many common plants growing in and around our yards are naturalized non-natives.

We may also hold a dim view of pioneer plants since they can be associated with altered or degraded spaces. As already mentioned, these plants are often robust and may survive, if not thrive, in conditions that many native plant species cannot. As newer comers, pioneer plants may lack natural predators or controls to initially keep their growth in check. Over time, however, this competitive advantage can diminish as existing species adapt. It’s important to remember that many opportunistic plants don’t create the altered conditions they are happy to occupy; they are simply better able to take advantage of new niches created by disturbance, poor soil fertility, soil compaction, creation of greater edge habitat from road or trail building, etc.

There are also plants (native and non-native) that do modify their surroundings in ways that make conditions less hospitable to other plants. These are known as allelopathic plants. Black walnut, for example, emits chemicals that inhibit the growth of nearby species. Other trees use their roots to pull in water to increase their competitive advantage. It is useful to learn which plant species are allelopathic as this should influence how they are managed. Some examples include spotted knapweed, common reed (Phragmites sp.), purple loosestrife, and garlic mustard.

An area of poor topsoil dominated by spotted knapweed - this area is currently being sheet mulched to add organic matter and improve soil fertility
Area of poor topsoil dominated by spotted knapweed

Garlic mustard is an interesting case since it disrupts associations between mycorrhizal fungi and plant roots. The symbiotic associations between fungi, plants, and trees allow for the exchange of nutrients, water, and other essential information such as distress signals about drought, disease, insect attacks, etc. As an aside, approximately 29% of plant species don’t need to associate with mycorrhizal fungi, of which the mustard family is included. More recent research on garlic mustard, however, has indicated that its spread “might be an effect rather than a cause of changes that are occurring in native ecosystems.” Like other feared “invasives”, garlic mustard may “largely be riding on the coattails of favorable environmental changes driven by humans.”

Once we start viewing “invasives” as a symptom rather than the root problem, we can learn interesting information about the ecosystems they successfully inhabit, including the environmental changes that have tipped the balance from supporting natives to giving introduced species a competitive advantage. Remember, it is hard for a new plant to “invade” an intact ecosystem, that is, unless changes have opened new niches that a new comer can exploit (assuming they have the appropriate traits to begin with). Thanks to their ability to thrive in tough conditions, introduced species can help fill voids left after more sensitive plants have either been directly removed or conditions altered to a point that they can no longer survive.

Nature hates a vacuum and works hard to prevent open ground from staying bare. I personally find it heartening to know that there are plants able to eke out an existence in very inhospitable conditions. This highlights nature’s resiliency, even if the early stages of recovery aren’t always beautiful or inviting.

Productively Using Opportunistic Plants (i.e., ecologically management invasive species)

When we think about useful plants, we rarely include weeds – unless you are an herbalist and then you seek out potent weeds! Yet when it comes to repairing degraded or disturbed land, these pioneer species are incredibly useful since they help protect the soil by quickly establishing and increasing their numbers. In these situations, the soil ecosystem has likely also been impacted and needs to recover. Healthy and diverse soil biology is essential to overall soil functioning, including nutrient cycling, water infiltration, degradation of pollutants, and soil structure improvement (to name just a few). When I encounter an area with pioneer plants, I “read” the landscape to give me clues about its health as well as steps I may want to take to restore soil health and/or support certain plants over others (see Part 2 for more specifics).

Plantain is one example of this. European settlers originally brought plantain over and because it started growing along the trails they used, Native Americans referred to the plant as White Man’s Foot. The presence of plantain indicates heavy clay, waterlogged, or poorly drained soil, possibly tilled or cultivated that may also be acidic or low in lime. I’m sure plantain was present back when we moved to the farm, but its population has definitely increased as we have created favorable conditions where we have built infrastructure or compacted by driving or repeatedly walking on. I use plantain as a medicinal plant, so I appreciate its presence but I also know what I would need to do if I wanted to reduce the number of areas it grows (i.e., stop compacting the soil followed by mulching).

Plants with deep tap roots (such as thistle, dandelion, wild carrot, and burdock) are other examples of plants that can indicate areas of highly compacted soils. In this instance, nature is providing the very solution – decompaction – needed to improve soil conditions. Prickly or thorny plants that move into a disturbed area are examples of protector plants. Basically they are nature’s way of saying “do not enter” or “work in progress”.

It’s easy to overlook the gradual and sometimes invisible healing process Mother Nature undertakes, especially because a lot of the hard work is below ground. It also doesn’t help when we readily dismiss plants as weeds (i.e., bad) that we must wage war against. The nutritious and medicinal dandelion comes to mind! Moving away from labeling plants as either good or bad has encouraged me to approach each plant with an open mind and an interest in learning more.

Work Smarter, Not Harder

When managing non-native plants, I also try to view the landscape from the perspective of wildlife. Humans have the luxury of supplying our needs from a store so it’s easy for us to view an introduced plant as a nuisance without evaluating any other useful properties. As the human footprint continues to spread and degrade ecosystems (whether directly or through climate change), we make it harder for wildlife to adapt and thrive. Not all introduced plants are initially beneficial or edible for wildlife, but overtime ecosystems evolve and anything that becomes too numerous will eventually become food for something (either by directly eating it or by infecting it to reduce the population).

As a forager, I observe and interact with the land in different ways and find it easier to see things from the perspective of wildlife. My earlier views on non-natives being “bad” were initially challenged by these observations. Take spotted knapweed as an example. Our native bees have no idea that this plant shouldn’t be here and can be regularly seen harvesting nectar from its abundant flowers. Overtime as I gained more experience working with various plants, I learned new ways of ecologically managing them as a resource. Autumn olive is a perfect example. Wildlife and livestock love the nutritious late season berries as well as its trait of keeping leaves into early winter (the deer and our goats appreciate this trait!).

Autumn olive is a nitrogen fixing plant that produces many late season berries that are nutritious and edible for wildlife, livestock, and humans
Nutritious autumn olive berries

Taking the time to learn about the various plants growing around us (natives and non-natives alike) encourages us to find novel uses for them, which goes a long way in controlling joyful growers. At least with these plants there is little danger of over harvesting! Going back to autumn olive, since I am not afraid of killing this plant, I regularly use it for “chop and drop” mulch as well as to provide ramial wood chips for our apple trees in the spring (this helps feed the mycorrhizal fungi that the apple trees partner with). This along with harvesting the large berry branches in the fall allows me to both use and control this plant at the same time.

The thing that really forced me to rethink how we manage “invasive” plant species was the increasing reliance on toxic chemicals for their control by well meaning people. I hope that by looking for beneficial uses for these plants, more people will stop using toxic chemicals in an attempt to control these opportunistic plants. These chemicals are futile because they don’t address the underlying problems that have allowed introduced plants to successfully occupy new niches created by human activity. Setting aside the obvious health risks of using toxic chemicals, chemicals also destroy the very soil biology that many of our favored native plants require to survive and thrive. Chemicals make a bad situation worse and may in fact create conditions that continue to favor non-natives even more.

In Part 2, I discuss the specific plants we are targeting and how we are using, controlling, and/or removing them. We rely on physical removal and added goats in 2022 to help us control a variety of plants. With the right approach, we can take use the very traits that give an introduced plant a competitive advantage against them.

Nigerian dwarf goats eating autumn olive plants in early winter to help control invasive plant species
Niko and Nibler enjoying the late season berries and leaves of an autumn olive plant


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