Ecologically Managing Invasive Species Part 2: Turning Problems Into Solutions
In Part 1 of this series, I discussed why and how I adopted the view that invasive plant species are a symptom rather than the root problem. The term “invasive” is relative and indicates a plant growing where we don’t want it. Ecosystems are constantly evolving, with species coming and going over time. Thus, the term “native” is also relative and plant communities will continue to shift as our climate continues to change. Furthermore, the spread and/or establishment of introduced plant species is often an effect of the various human-caused disturbances around the world rather than a malicious intent by pioneer species.
As mentioned in Part 1, I use a number of terms interchangeably to reference “invasive” plant species, including introduced, non-native, opportunistic, pioneer, and joyful growers. Every plant had to “invade” a new area to become established, so I avoid labeling plants as either good or bad. Different plants simply have different traits that allow them to interact differently with the environment.
Not all introduced species become invasive, especially when they are introduced to healthy or intact ecosystems. When a niche or gap opens due to natural or human-caused changes (i.e., a wind storm that knocks down a large tree creating an opening in the canopy or building a road that opens the canopy), it creates opportunities for species that can quickly take advantage of the disturbance. Climate change is a wild card placing new stresses on many ecosystems and creating openings for new comers to become established, even in areas less directly impacted by other human changes.
How We Manage Opportunistic Plant Species at Apple Acres Farm
Viewing pioneer species as potential allies makes it easier to want to learn about them, including finding productive uses for these plants. The more I learn about wildcrafting and herbalism, the more I believe that nature provides the very plants we need in our lives. I therefore take notice of plants that both catch my attention and are thriving around the farm – regardless of whether they are native or non-native.
Many pioneer species provide environmental benefits that are easily overlooked, such as fixing nitrogen, bioaccumulating contaminants (these plants should not be consumed or used for medicine), dynamic accumulation, and soil decompaction. Some are also edible, and/or medicinal, such as dandelion, plantain, burdock, and yellow dock.
Below I discuss in more detail a number of joyful growers we are managing or beneficially using around the farm. I’ve included wild apple trees because they exhibit traits that can be associated with being “invasive” (i.e., non-native, spread by wildlife, readily escapes cultivated areas). This offers a useful example of the power of labeling plants as good or bad in terms of how we perceive or overlook their particular traits. Here are the plants I'll be discussing if you want to jump ahead to a specific section:
Each opportunistic plant species is managed differently depending on where its growing, whether it’s edible (for humans, livestock, or wildlife), whether it has medicinal properties, whether it’s providing free environmental services, or whether it can be used for mulch, firewood, etc. In some cases I’m not actively managing a plant population but rather observing how it’s fitting into the ecosystem, whether it’s spreading, etc. If I determine something needs controlling or removing, then I figure out ways to productively use it rather than focus solely on eradicating it.
Since many pioneer species struggle under shade or partial shade conditions, shade becomes a management tool. When we want to cultivate (i.e., regularly disturb) an area or halt its natural ecological succession, such as by keeping areas open or non-forested, then we need to understand that we are making conditions more favorable for many pioneer species. Around the farm, that means these areas will require more active vegetation management than if we allowed them to return to forest.
I also think it’s wise to approach introduced species with a “wait and see” perspective since we don’t know what is in store for our area climate-wise. Each year there are more extreme weather events as well as hotter and drier summer growing conditions. Allowing a diversity of plants to coexist while we do our best to adapt to a changed and changing climate seems wise.
One final thought before we discuss specific plants. As a regenerative farm, we apply the permaculture principle of reframing problems as solutions. Below you’ll find specific examples of how we do this, but in general this idea helped me understand that we didn’t have an invasive plant problem, we had a goat deficiency, which we finally corrected last summer. If you have an interest and the ability to use animals to ecologically manage vegetation, I highly recommend it! It makes the work more enjoyable and produces more effective results when done well.
Meet Our Joyful Growers
This deciduous shrub was introduced as an ornamental plant to provide food and cover for wildlife as well as to help with erosion control. It grows well in disturbed areas and will readily spread if trees have been cleared or in open areas reverting back to forest. On the farm, we primarily find autumn olive in former pasture land, especially where there is poor topsoil (this is a common theme for most of our joyful growers). Occasionally we may find autumn olive saplings growing in forested areas, but these individual plants don’t seem to be thriving and don’t produce berries under the shady tree canopy. Autumn olive is also not very winter hardy and older branches tend to die back each year.
Autumn olive has small thorns, grows up to 20 feet tall, and can grow in dense stands. It also fixes nitrogen, which is beneficial in our old pasture areas as well as in our apple orchard. Some people even plant autumn olive as a nurse tree for newly planted fruit trees with the intent of eventually removing the autumn olive once the fruit tree is established. While we value this nitrogen fixing trait, it can cause problems in certain ecosystems with plants adapted to thrive in low nitrogen conditions.
We haven’t found autumn olive particularly difficult to remove or control but it does take effort. The most direct way to remove these plants is to pull up it up, roots and all. It can also be mowed or manually cut down but this often requires follow up removal to deplete the root reserves over time (for us that has been years). Since I like to use this plant’s plentiful growth, especially now that we have goats that eat the foliage, I tend to focus more on controlling rather than removing it.
A couple of years ago we also experimented with using pigs to clear an area of dense understory growth of autumn olive. To help the pigs, prior to setting up the portable electric fence, I trimmed back many of the mature plants (using the cuttings to mulch the previous area they had rooted up). This may not have been necessary, but it made it easier to move the fencing and the mulch was beneficial for the previously disturbed area.
After we added chickens, I decided to leave several strategic patches of autumn olive near the coop and barn to provide predator protection for our flock. Adult chickens are also jerks, so once we had our first farm-raised chicks we appreciated these patches for the younger birds. Chicks are much more vulnerable to predators and ours appreciated having a safe refuge away from the bigger chickens.
Initially, I was frustrated by the prodigious regrowth of autumn olive, but as mentioned above, I turned a problem into a solution by using these plants as plentiful source of ramial wood. This wood comes from the small younger branches (less than a couple of inches in diameter) and is the most nutritious part of the plant. This is also the type of wood our goats prefer to eat. When we were building and had bare soils, rather than buying straw, I used the autumn olive trimmings as mulch to reduce erosion and runoff until the land disturbing activities were completed and we were ready to re-vegetate. Ramial wood chips also feed the mycorrhizal fungi that partner with our apple trees when apply it as a spring mulch in the orchard.
Autumn olive produces plentiful late season berries that are nutritious and edible for wildlife, livestock, and humans. The tart berries contain vitamins, minerals, proteins, and essential fatty acids (rare in other fruits that grow in our zone 4 climate). Our honey bees appreciate the blossoms and we use the berries to feed our chickens and goats as well as to make fruit leather (mixed with apples – it’s delicious!). I also dry the berries for livestock snacks in the winter months. Overall, this is one of our best fall foraging plants, with the chickens and goats actively seeking out the berries (along with other wildlife).
Prior to using goats, our primary control method was (and still is) harvesting the berry branches each fall by cutting them off. This does several things at once: it provides us with a renewable ramial wood chip source and it keeps the plant pruned (i.e., controlled). By pruning these plants at deer or goat browsing height, we also enlist their help in keeping the plants’ future growth in check.
Autumn olive and buckthorn (discussed next) were the two primary plants we wanted goats to help us control. Unfortunately, Niko and Nibler were not initially interested in eating autumn olive. This was disappointing but not entirely surprising since they were raised on hay and had never been taught which plants were edible. Luckily, they gradually expanded their palettes over the summer and by the fall they warmed up to autumn olive. It certainly helped that like other non-native plants, autumn olive holds it leaves a month or two longer than many natives.
The berries also helped our goats appreciate the edibility of the rest of the plant. Niko and Nibler love all berries and by late fall, autumn olive berries are the only berries they can forage themselves. It wasn’t until the berry supply dried up that the goats began eating the leaves and twigs. Once all the lower branches were consumed, we helped them by cutting down the taller branches, focusing on areas we wanted to control this plant. This ends up being a bit of work for me (compared to the goats self-harvesting) but since I chip these trimmings and most other farm work is done by November, I don’t mind having an excuse to spend more time outside with the goats!
I’ve been asked if autumn olive berries cause digestive upset in our animals. The berries certainly turn their poop a reddish color but I’ve never noticed anything unusual in our chickens. Niko did have looser stool for a day or two when he was primarily eating the berries, but he has a more sensitive digestive system and our other goat doesn’t have this same problem was completely fine. This cleared up quickly in Niko once we started moderating the goats’ berry consumption.
Like many other berry producing plants, autumn olive is spread by seeds. Another concern people have is whether we are increasing the spread of this plant by feeding the berries to our animals. In the three years we have been doing this, I haven’t noticed any increase in this plant in the areas that our animals spend more of their time (i.e., where they would deposit the seeds via their poop). Cooking the berries also kills the seeds, so I also don’t worry about composting any seeds I remove when making fruit leather.
Of all our joyful growers, buckthorn was my least favorite until we addressed our goat deficiency. Common buckthorn was planted as a hedge along a property line where it has been spreading in the surrounding fields that are in various stages of reforesting. Glossy buckthorn has found its niche in the edge habitat around our stream as well as in some swales. Unlike other opportunistic plants we find around the farm, buckthorn can tolerate growing in shady conditions, which gives it the ability to establish in the forest understory. It also has nasty thorns, so it’s a good idea to wear good work gloves when handling this plant.
When we first moved to the farm, I was surprised by the size of the oldest common buckthorn trees. Not surprising, the ground beneath these thriving trees was carpeted in seedlings and saplings. Until we had Niko and Nibler, I largely ignored these smaller plants since I knew they would be an easy food source for the goats. In areas that this plant has been spread by seeds, I do regularly look for and pull individual plants when I’m out foraging. When I notice a higher concentration of seedlings I know to start looking for a nearby seed tree!
I usually cut down buckthorn trees with the goal of leaving three to four foot tall stump(s) to encourage deer browsing of the new growth. Over the years I’ve noticed that several of the stumps growing in more shaded areas were eventually killed from repeated browsing, while those in sunnier locations continue to resprout.
There is a lot more buckthorn growing off of our property than on it, so in the future I will talk with our neighbors to see if they would allow our goats to help control its spread. I think I’ve found most of the seed-producing trees on our property at this point, so securing new supplies of buckthorn for fall feeding would be useful!
Aside from providing food for our goats, the main benefit we’ve derived from common buckthorn is its higher BTUs. When I cut down seed trees, we use the larger diameter wood for firewood and chip the rest. Glossy buckthorn is a softer wood, so everything gets chipped. Buckthorn is allelopathic and can alter the surrounding plant community, so these woodchips are good in paths and other areas that we don’t want vegetation establishing.
Like autumn olive and other non-natives, buckthorn holds its leaves and berries into early winter. It also tends to be one of the earliest plants to green up in the spring. This makes it easy to identify and remove. Before we had goats, I would often take advantage of the winter snow pack to cut and haul trees in dense areas (via snowshoe). Now that we have goats, I cut buckthorn down in the fall when the trees have the most value as a late season food source. The goats prefer common buckthorn to glossy buckthorn, though as other wild food supplies dwindled this past November (including common buckthorn), the goats were happy to revisit the glossy buckthorn!
Most buckthorn trees are too tall for our goats to browse, but they readily eat the dense patches of seedlings and small saplings. We use a portable electric fence to help focus their attention in these areas. Prior to goats, we had some success using the rooting behavior of pigs to eliminate some seedlings. Buckthorn seeds can remain viable for up to 5 years, so repeated browsing or rooting is required to take care of new seeds that germinate. Obviously, it is best to first prioritize removing any seed trees. It’s not easy setting up electric fencing in most areas where our common buckthorn grows due to the dense understory growth these trees can tolerate (and help create). It therefore requires a lot of pre-work to cut out a clear path for the fence itself. Over time I’m optimistic it will get easier to browse the goats in these areas.
Once hunting season starts, we keep the goats away from the main buckthorn areas since they are near the property boundary. Thus, along with autumn olive branches, I end up hauling buckthorn cuttings back for our animals to eat. This isn’t enjoyable work but once the goats and chickens are done with these, I cut firewood from the larger wood and chip the rest. This fall we learned that the goats love to nibble on buckthorn and autumn olive woodchips, so moving forward we will replenish the mulch around the barn with these plants.
Our chickens also eat buckthorn berries, though they don’t enjoy them as much as other berries (especially not compared to autumn olive berries). Buckthorn berries can produce a laxative effect, especially for smaller wild birds, apparently resulting in death in extreme cases. We don’t have many buckthorn stands in areas frequented by our free-range flock, so they primarily eat berries off the trees we haul back for the goats. It’s possible that the small amount of buckthorn berries consumed by our chickens is not enough to produce any digestive issues in either our chickens or goats.
Spotted knapweed is a common weed thanks to its ability to thrive in disturbed and poor soils as well as its allelopathic properties that alter soils to reduce competition from other plants. We have two areas where topsoil was removed by a previous owner and they both are dominated by spotted knapweed. I’ve tried a number of strategies to control this hardy plant, including hand pulling, scything before they bloom (to prevent them from setting seed), and sheet mulching to add organic matter and improve the soil (while also smothering the plants).
Its seeds remain viable for up to 8 years, which is why I originally focused on preventing it from going to seed. In the last year I’ve mostly stopped this practice because after observing its response to my control methods, I’m less concerned about it producing seed and spreading to new areas around (or off) the farm. I also see bumblebees regularly visiting spotted knapweed blossoms. Habitat loss is a major issue for pollinators so I do what I can to support them by leaving as many areas as wild as possible to ensure they have a steady supply of nectar over the growing season. It’s taken me many years, but I’ve finally stopped discriminating between native vs. non-native flowers. Instead of pulling or scything spotted knapweed (with blossoms or not), my efforts now focus on improving soil conditions to favor other vegetation and lessen the competitive advantage of this hardy plant.
Back in 2020, I experimented with using pigs to root up and fertilize one of the areas where topsoil had been removed. Since this plant does well with disturbance, there were questions about whether pigs would make conditions more favorable for spotted knapweed. It was a very hot and dry summer so I didn’t keep the pigs in that area as long as planned (they were moved to an area with a thick understory of autumn olive), but I was pleasantly surprised with the vegetation that grew the following year. The overall amount of spotted knapweed was reduced and the existing seed bank produced a nice variety of wildflowers and grasses.
Spotted knapweed doesn’t tolerate shade very well, so the year following the pigs, I planted a black walnut guild (plant community) to establish a kind of silvopasture system. Silvopasture is an agroforestry practice that integrates trees and pasture into a system for raising livestock (in our case, goats and honey bees). Our black walnut guild includes mulberry trees, hazelnuts, comfrey, horseradish, anise, echinacea, and lovage. I selected black walnut intentionally to use its allelopathic properties to deter other trees from establishing (the plants in the guild are able to grow near black walnut). The eventual shade created by the larger trees will further reduce the spotted knapweed while also providing shade and food among other benefits.
When we added goats in 2022, their summer sleeping pen was set up in the same area we had initially put the pigs. I immediately began feeding the goats young spotted knapweed plants as we worked to transition them away from the hay diet they were raised on. In addition to eating the spotted knapweed, the goats are continuing to fertilize this area. Each year, I also add additional organic matter in the form of hay and straw, leaves, apple drops, and woodchips.
The second and larger area of spotted knapweed is located further away and is receiving a different treatment. For the past four years, I’ve been gradually sheet mulching to smoother the spotted knapweed while also improving soil fertility. I started this process when we were building (before we had any livestock) and we had plenty of scrap (unpainted) drywall and cardboard. Gypsum is a widely used soil amendment and provided a nice weight to keep the cardboard from blowing around. Since then, most weeks I add coffee grounds from local hotels as well as other organic wastes we don’t use elsewhere. The goats discovered this stash of old coffee grounds and enjoy sneaking off to get their fix in the summer!
The sheet mulching effort is generally working; however, I would have better results if I had concentrated my efforts over a shorter period of time. Instead, I add materials as I have them and we haven’t yet made a path to get the tractor up to chip the buckthorn trees I’ve dragged over or the diseased Juneberries I have yet to cut down. It is encouraging to see healthier plant growth in the spotted knapweed and other vegetation since that indicates the soil fertility is improving. This coming year, I hope to level out the various materials I’ve piled up, add a new layer of cardboard over the entire area, and top it all off with a nice layer of woodchips. If all goes well, I’ll eventually grow grains, corn, winter squash, and other larger crops that take up too much room in our main vegetable garden.
Deep Tap Rooted Plants
We have a variety of hardy deep tap rooted “weeds”, such as dandelion, wild carrot (Queen Anne’s lace) burdock, yellow (curly) dock, and thistle. I’ve lumped these plants together since they are happy to grow in heavy compacted or disturbed soils and they do not tolerate or thrive in shade conditions. Aside from their medicinal and/or edible qualities, I also appreciate these plants because they decompact soil, build organic matter, mine minerals from the subsoil, and provide food, building materials, and shelter to wildlife.
Each fall I manage some of these plants by harvesting their edible roots. I even went so far as to spread burdock seed two years ago because I had lost my previous supply of burdock elsewhere. For the burdock, I seeded areas heavily compacted from construction activities that are in various stages of being sheet mulched. While all of these plants do grow in compacted soils, if I wanted to produce larger tap roots that were easier to harvest, I would have grown them in better soils. However, my goal was to harness the free environmental services they provide to improve areas with poor soils. Burdock is a biennial and when it goes to seed this year, I will harvest the seed to avoid it spreading to other areas.
I also harvest seeds from several of these plants. I hope to use them for culinary purposes in the future but for now the chickens enjoy these wild seeds in the winter. If this topic interests you, check out Katrina Blair’s book The Wild Wisdom of Weeds. Aside from eating these plants, I also harvest some to make teas and herbal tinctures. One downside of having a naturalized population of wild carrot, however, is that it readily crosses with cultivated carrots if you are saving seed. I don’t plan to eradicate wild carrot any time soon but I do want to save carrot seed, so luckily wild carrot doesn’t grow everywhere (just near the gardens!).
Thistle is the only plant in this group that I don’t harvest for food or medicine. I’ve been trying to introduce it to the goats, but they don’t yet have an interest in it. So I’m mostly watching it and managing it in areas we’ve disturbed as well as around the gardens. There are native thistles and I don’t yet know enough about the different species to feed confident in prioritizing its removal from other areas. These thistles don’t appear to be taking over and some years they’ve even looked a little sickly and didn’t produce blossoms.
This perennial originated in Europe where it was used as a medicinal herb. It readily self-sows as well as grows from underground rhizomes. Tansy grows in a variety of soils and tolerates dry and poor soils as well as some shade. It’s reported to be a natural insect repellent though we don’t have any growing near the house so I can’t speak to that. I’m also not particularly drawn to tansy, so I haven’t tried using it medicinally or even as a natural dye.
The primary way I’ve used tansy is as mulch in the garden since it adds potassium to the soil. Its leaves can also be added to compost piles to increase decomposition. In the places where tansy grows here, it rarely grows as a monoculture so I haven’t used sheet mulching to avoid indiscriminately killing the vegetation it’s coexisting with. To effectively smoother tansy, you would want to use several layers of cardboard.
In areas I’ve repeated harvested tansy for mulch, I’ve noticed a reduction in the overall tansy population. There is one spot with a lone Jack-in-the-Pulpit that I still pull tansy from and it seems to be doing well (though I’d love to see more Jack-in-the-Pulpits in that area!). I’m also not worried about the tansy colonizing an area near a stream that was washed out by a large flood event, since pioneer species are effective at quickly covering bare soils. The washed out area is also very steep and sandy since it used to be dammed up. Thus, trying to reseed this area with something else would likely result in more disturbance as well as wash more soil into the stream.
I haven’t yet introduced the goats to tansy mostly because it doesn’t grow densely in areas that I forage them. In fact, the Jack-in-the-Pulpit area is next our road and our neighbors have somewhat aggressive dogs that I don’t want the goats meeting. I assume if they were to encounter this plant at the right growth stage they would eat it.
Japanese barberry is often planted as an ornamental shrub that readily escapes yards and gardens and is considered an aggressive grower. A few years ago I stumbled across one plant growing down in a rather unusual spot – down in a swale in the forest understory. I was excited because this is an incredibly medicinal plant that has a long history of use in Ayurvedic and Chinese medicines. I plan to keep the mother plant and manage new growth by harvesting off-shoots each fall to make herbal tinctures.
The roots contain a yellow plant extract that indicates the presence of the bitter-tasting alkaloid berberine. Other medicinal plants with berberine are goldenseal, Oregon grape, and tree turmeric. None of these plants are currently growing here, so I’m happy to make use of this volunteer berberine-containing plant that may have a use in treating Lyme disease (among its many other medicinal properties).
This fall when I harvested barberry, I left the top growth out for the chickens and goats to examine (it grows far enough away and in a location that our animals wouldn’t likely come across the plant). Initially both were interested in the bright red berries and the goats even tried the small leaves; however, they quickly lost interest. Goats theoretically like to eat barberry so perhaps if we had more plants they would develop a taste with more exposure to it?! I always keep an eye out for volunteers but so far I haven’t see any.
Apple trees are not native but enjoy a generally positive reputation. Yet, wild or feral apple trees pop up all over our farm and must be controlled each year. Like other non-natives that are treated as “invasives”, apple seeds are spread by wildlife. When we moved to the farm, the original apple orchard had not been maintained for years (decades?) and wild apple saplings and trees were crowding out the understory of our mature apple trees as well as joyfully growing everywhere in the old pasture areas. Prior to adding goats to help us manage vegetation, I used to spend a similar amount of time managing our wild apples as I did buckthorn.
Fortunately there are a lot of benefits of apple trees besides their apples, hence why society doesn’t typically don’t considered them as an “invasive”. Apple wood is high in BTUs so the larger diameter wood is used for firewood while the smaller dead wood makes nice kindling. I chip the smaller diameter branches (from live trees) to make ramial woodchips that are used as mulch in the apple orchard (as discussed in the autumn olive section).
Each spring I also scythe around our apple trees under the drip line. This mowed material feeds the mycorrhizal fungi thanks to the corresponding root dieback by the plants which helps them match the shortened above ground growth. From a management perspective, this annual mowing also cuts back any emerging saplings (apple or other).
It takes a lot of work to revive an abandoned orchard and so far we have focused on the trees growing closer. We still have dozens of trees that we haven’t done much work on and I’m planning to use the goats to help with that future work. They happily eat new saplings and will prune low branches, which is great in the old pasture areas. It is very easy to get the goats to focus on browsing apple trees since they love the leaves, twigs, and fruit. We help direct their attention by setting up the electric fence around trees we want to work on. This requires initial clearing work to even be able to set up the fence, but luckily the goats (mostly) take care of the rest.
While every site is different and each area has its own opportunistic plants, hopefully this information inspires you to look for beneficial ways to use your joyful growers. By moving away from labeling plants as either good or bad, I've become more interested in examining how they got there, why they’ve been able to establish, and what conditions would deter their ability to survive or spread. This curious and open mindset makes it easier to turn perceived problems into solutions. Best of luck!