Common buckeye

A common buckeye is one of many late-summer species of butterflies that gets nourishment from black knapweed. American goldfinches also eat its seeds. (© Marlene A. Condon)

“The eye sees only what the mind is prepared to comprehend”  — Henri Bergson, French philosopher

In the January-February printed edition, the Bay Journal noted that the nonnative hydrilla “has become important in the Bay as a ‘pioneer’ species, colonizing unvegetated areas and making them suitable for native grasses.” People working for the federal government long ago realized that some alien plants, like Hydrilla verticillate, perform better than native plant species to repair degraded environments, which is why many plants now referred to as “invasive” — such as autumn olive (Eleagnus umbellata) — were brought to the United States in the first place. Autumn olive helped with mine reclamation in the 1830s.

Was it a mistake to bring such plants to this country to help fix the destructive impact of humans on the environment? In my opinion, no. With an increasing population, accompanied by development of the land, and with increasingly warmer and droughty conditions due to global climate change, some of the so-called invasive species could be the unintended saviors of our wildlife. But, to see it that way, people need a better understanding of soil science and how the natural world works.

For example, it’s common to see abandoned fields and roadsides in Virginia filled with autumn olive as you drive throughout the state. You could easily believe the dogma that these Asian plants “pushed out” native plants and took their place, but, simply put, you’d be wrong. Without an assessment of prior land use and the soil itself, you can’t possibly come to a reality-based conclusion about why certain plant species grow in these areas.

Generally speaking, both roadsides and unused fields are compacted and nutrient poor. In fields, that’s either because half-ton cows trod over them day after day or because the crops required heavy machinery to “prepare” the soil, sow seeds, and care for and harvest the plants every year. Roadsides are compacted by the heavy machinery used to prepare the roadbed, and they are usually bereft of nutrients because the topsoil has been removed, leaving behind a dense subsoil comparatively devoid of organisms and nutrients.

Therefore, the plants you see as you drive along highways and past neglected farm fields are only the plants capable of growing well in those inhospitable soils. They rehabilitate the soil for the benefit of native plants that require good (that is, crumbly and nutritive) soil in which to grow well. Only after the “pioneers” like hydrilla and autumn olive have done their work can such plants move into these impaired locations.

Native pioneer plant species are few in the Piedmont region of Virginia (where I live), consisting mainly of Eastern redcedar (Juniperus virginiana), Virginia pine (Pinus virginiana), Eastern white pine (Pinus strobus in mountainous and foothill areas), broomsedge (Andropogon virginicus), and, though not actually native to this part of the state, black locust (Robinia pseudoacacia). You will often see these plants joined by autumn olive, a hint that supposedly invasive plants are simply nonnative-pioneer plants, increasing the diversity of plant life and thus animal life in these areas.

Autumn olive shrubs and black locust trees in fields and roadsides share an extremely useful attribute: the ability to fix nitrogen and thus enrich poor soil (a desirable trait of peas and beans that is often employed by gardeners for that reason). Such plants serve as Mother Nature’s nitrogen cooperative, working with bacteria that enrich the soil by adding this vital nutrient — making it less necessary for us to squander limited resources like petroleum in making synthetic fertilizer.

Unfortunately, the predominant narrative nowadays is that everyone must remove supposedly invasive plants that are mistakenly believed to have displaced native plants while not offering their ecological benefits to the environment. It’s a false narrative, but not surprising, given that people are prepared to understand only what their own biases and limited experiences allow. Yet anyone can find out the truth about these plants. It’s not rocket science; you simply need to observe the natural world without preconceived notions and grow these plants on your property.

I’ve observed in my own yard how black knapweed (Centaurea nigra), Japanese honeysuckle (Lonicera japonica), autumn olive and the royal paulownia tree (Paulownia tomentosa, aka empress tree) feed our pollinators with blooms, nourish birds and mammals with fruits, seeds or buds, and even furnish nesting material and/or sites. In years when deer overpopulated the area, they denuded my yard of most native plants, which would have destroyed all habitat if I hadn’t included commonly disparaged invasives in my yard that deer didn’t eat. It’s often overlooked that deer are capable of eradicating native plants, leaving the false impression that the natives have been driven out by nonnatives.

In the severe drought years of 2002 and 2003, I witnessed how native species withered alongside the roads as I drove to Shenandoah National Park to give monthly slide presentations. Meanwhile, alien species continued to flourish despite drought and drying winds.

If you care about wildlife, ignore the siren call of voices who frame the invasive plant “problem” in terms of morality, suggesting it is your “duty” to destroy these plants. They couldn’t be more wrong.

Marlene A. Condon is the author-photographer of The Nature-friendly Garden (Stackpole Books 2006). You can read her blog at InDefenseofNature.blogspot.com.

The views expressed by opinion columnists are not necessarily those of the Bay Journal.

NOTE: The comment period for this opinion column is closed.

(35) comments

Marlene

To hydrophilac: What's missing from your narrative is the concept of the passage of time and human activity being the reason these so-called invasive plants are in this country.

Germanium lucidum is a garden plant, as is English Ivy. Cheatgrass arrived in the mid- to late-1800s as a contaminant in seed and straw. If environmental conditions nearby suited the spread of these plants, that's a natural occurrence. People shouldn't speak of the plants as if it's their fault they were brought here and were able to do what plants do in circumstances favorable to their existence: grow, reproduce, and spread. If those declining sage-steppe species were asked by someone about cheatgrass colonizing areas which could not be colonized by native plants, I imagine they would give that person a darn funny look only because people were responsible for this situation.

You are overlooking the fact that plants do not fill in areas overnight. It takes years, and certainly in some cases, decades. When you come along and see an area filled with a nonnative plant, you really need to know the history of that location to understand why only one particular species was able, apparently, to fill the space. Either the lighting, moisture levels, soil conditions or a combination of these factors determined which species would out-compete the others (again, a natural occurrence).

Unfortunately, people don't tend to see what impedes their beliefs as must be the case with your not having yet seen a pollinator on the geranium, but many solitary bees on each of the different natives. For those geraniums to reproduce, there MUST be pollinators, which may not be bees, but it's obvious that some type of critter is, without a doubt, making use of those plants.

If there's English Ivy in salmon country, that's very surprising because it could only be in a wilderness-type area because someone once inhabited the area--which means disturbance of many sorts, a well know reason for "invasive" plants to be there. If many rivers are lined with ivy banks, they can't be filled with sediment because such a thick ground cover certainly holds the soil in place.

When people disregard these truisms, and the fact that humans are responsible for these difficulties, they are disregarding reality. It's well known that "invasives" do well in disturbed conditions. It's also known, by plant scientists, at least, that plants can improve soil conditions; otherwise there would be no such thing as succession. So yes, you can remove nonnative plants that have been growing for a long time and native plants might be able to "re-invade" the area, but they do so thanks to the efforts of the plants that existed there for years.

(Edited by staff.)

Conservation Sense and Nonsense

Hydrophilic reveals that he is employed by the “restoration” industry, which probably influences his perception of the success of his eradication projects. Here’s another way to interpret what he perceives as success.

• He says non-native G. lucidum germinates after the first fall rains while native plants are dormant until spring arrives. He claims that once it occupies the ground, natives are unable to return. G. lucidum has shared my garden with native Fragaria for many years without gaining ground. In fact, Fragaria dominates. G. lucidum is not considered invasive by the California Invasive Plant Council (it is on the “Watch” list). Since it blooms while natives are dormant, it is providing forage for pollinators when natives are dormant. If herbicides are used to eradicate G. Lucidum, returning natives are probably stunted by pesticide residue and damage done to the soil by the herbicides.

• Ivy is incapable of killing trees. It climbs up trunks, but not into the canopy where some other vines are capable of killing trees. Occasionally you may see a leaning, dead tree that is covered in ivy. The tree died first, then the ivy climb up the leafless, leaning tree.

• The suggestion that warmer water in streams is caused by ivy occupying stream banks is illogical. Banks covered by vegetation contribute less sediment to the water, not more. Eradicating ivy is likely to produce more sediment because it will take some time for replacement vegetation to cover the ground, especially if herbicides are used to eradicate the ivy. Water is warmer in streams because of climate change and/or because there is less water due to water diversion or droughts. There are many other reasons for declining populations of salmon, particularly dams that prevent salmon from reaching their spawning ground upstream.

• Both species of ground ivy considered “invasive” in California produce flowers and fruit: “The flowers are greenish-yellow with five small petals; they are produced in umbels in autumn to early winter and are very rich in nectar. The fruit is a greenish-black, dark purple or (rarely) yellow berry 5–10 mm diameter with one to five seeds, ripening in late winter to mid-spring. The seeds are dispersed by birds which eat the berries.” (Wikipedia)

(Edited by staff.)

hydrophilic

Some specific examples of Invasive weeds out west "paving the way" for natives Germanium Lucidum germinates after the first fall rains once most of our native groundcovers have gone into dormancy until the following the Spring when they will begin to emerge. Since G. Lucidum germinates in the Fall and grows over the winter, by the time Spring rolls around it has formed a carpet of tall, sprawling invasive weed monoculture which prevents the native groundcovers from emerging. I have pictures of projects I have done where a diverse array of native groundcovers (Claytonia, Nemophilia, Viola, Enchanters nightshade, sweet mountain cicely, trillum, etc) either germinate or emerge shortly after invasive monoculture weed removal. If you are to count personal observations - I have yet to see a pollinator on the geranium and I have seen many solitary bees on each of the different natives. English ivy is an evergreen, non-native, invasive groundcover that has demolished undisturbed natural areas. The ground form does not flower and smothers out many native flowering groundcovers which would flower Spring-Summer. To top this off, it climbs trees and kills them. In salmon country that's the difference between clean, cold streams and warmer streams filled with sediment. I can personally show you many rivers which have had ivy banks for 50+ years. This is not paving the way for natives to recolonize. In fact, I have pictures of several projects I have completed where I removed this invasive monoculture which doesn't flower, and it was immediately replaced by several native groundcovers the following spring, most likely from the soil seed bank. Several native groundcovers, which all flower, are better than one invasive monoculture which does not (in its ground form). This was simple manual weeding, all the natives needed were a chance....they wanted to be there, and could be there...and there is no reason they shouldn't have been there. Cheatgrass in the west. Another example of an invasive weed that germinates long before many of our native grasses and forms a large monoculture carpet which prevents native grasses from emerging. It is utilized by deer only in the very early Spring, after it becomes useless. Cheatgrass is very prone to fires once it dies and therefore introduces more frequent fires to a landscape that is not used to frequent fires. This destroys sagebrush habitat for a VARIETY of species. Is this cheatgrass simply paving the way for natives to establish at a later date? Or is it displacing a diverse array of native grasses, forbs, and shrubs (which would otherwise exist perfectly fine) so it can therefore pave the way for them to re-establish in the future? If we could ask the declining sage-steppe species if cheatgrass was colonizing areas which could not be colonized by native plants I imagine they would give us a darn funny look. There are many other weeds I can talk about. Personally, If a non-native is not invasive I almost always leave it. I see pollinators visit oxeye daisy, field vetch, and others. It is wrong to broadly claim invasive weeds pave the way for natives to re-establish in the future. This may be the case for a specific micro-environment you live in but it is poor advice to extrapolate onto the rest of the country, if that's what you are doing.

(Edited by staff.)

Marlene

I was writing for what I saw as a limited audience, and not for the entire country. This said, however, the laws that govern the natural world are the same no matter where on Earth you are. The only differences between one area and another are the life forms.

Let's discuss Cheatgrass (Bromus tectorum). According to a USGS publication on Cheatgrass, "Many invasive plants thrive in disturbed areas and are easily spread through various pathways and vectors. In the western U.S., disturbed landscape can take the form of areas changed by human development, improper grazing, and burned by wildfire. Roads and trails, and the vehicles that travel them, transmission corridors, and fuel breaks all serve as pathways and vectors that help spread these unwanted invaders."

https://www.usgs.gov/centers/fresc/science/cheatgrass-and-medusahead?qt-science_center_objects=0#qt-science_center_objects

Voilà! The actual reason this so-called invasive plant has spread so much is human disturbance of the landscape. And let's not forget this plant was brought to this country because people insist upon bringing in all kinds of things from other countries instead of living within their own environment; Cheatgrass didn't arrive on its own.

Therefore this grass is a symptom of the real problem: the societal demand for goods and services that don't take environmental consequences into account, as well as the common lack of respect shown to our natural world.

The reality is that the entire "invasive-plant" issue places blame on the wrong entity entirely (plants doing what comes naturally) rather than the proper culprit--people! Unless and until you change the prevailing societal view of our natural world as something to use as humans see fit without taking into account the harmful consequences of their actions, fighting so-called invasive plants is futile and pointless. You can't fix a problem unless you fix the cause of it.

(Edited by staff.)

Conservation Sense and Nonsense

Hydrophilic repeats the standard dogma on which plant nativism is based and the sole source of that dogma, Doug Tallamy and his scientifically flawed books. In fact, there is little scientific evidence that supports the nativist dogma.

“Non-native” fruits are not less nutritious than fruits considered “native.” All fruits are native somewhere. How could all fruit in China be inferior to all fruits in North America? It’s tantamount to saying all white people are inherently superior to all people of other races.

Every species of native plant is closely related to all other members of the same genus, many of which are considered “native” in some distant place. Insects that can use “native” species in that genus are usually capable of using “non-native” species in the same genus. All life on Earth is related. Those who believe otherwise are apparently unaware of the 500 million year history of the evolution of plants and animals on Earth. Many species now considered “native” in one place existed elsewhere in the distant, pre-historical past.

Plant nativism has become a form of climate change denial. The National Park Service has announced the end of its 50-year attempt to re-create pre-settlement landscapes.

https://www.nytimes.com/2021/05/18/climate/national-parks-climate-change.html?action=click&module=Top%20Stories&pgtype=Homepage

Last month the National Park Service published new guidance for park managers in the era of climate change. The new guidance is a “reckoning” for NPS. One of the authors of the NPS report says, “The concept of things going back to some historical fixed condition is really just no longer tenable.”

The ecologist and science coordinator at Acadia National Park in Maine said, “We weren’t being trained on how to manage for change. We were being trained on how to keep things like they were in the past. We were probably always wrong to think about protected places as static. You have a whole profession of people having to shift how we think.”

Hobbyists can cling to their fantasy that the botanical clock can be turned back 250-400 years to pre-settlement conditions, but scientists and public land managers who follow their lead are moving on. The National Park Service led public land managers into the dead end of attempting to re-create historical landscapes. Now NPS will lead public land managers out of that dead end into the reality of a changed environment with a rapidly changing future.

Marlene

Dear hydrophilic, 

You should read through the other comments here as I've already addressed the points you've made, such as the fact that I was talking about nature-friendly gardening long before Doug Tallamy was, having appeared on Virginia Public Television to discuss my yard in 1994 and having written my book in 2005. It was published in 2006, a year before Bringing Nature Home. You might be surprised to know that I was given an advance copy of Bringing Nature Home to write a review of it, and what I found was a book filled with the usual misinformation about "invasive" plants, along with erroneous "facts", such as that no native predator fed on nonnative insects. It told me this man might know about leaf-eating insects, but as is the case with most scientists (due to their in-depth specialization) he didn't know much about what is actually taking place "out there". Rather than publicly panning his book, I thought it better (and more considerate) to inform Timber Press of the situation in, if I recall correctly, a 2-page listing of errors, which was just the tip of the iceberg.

Therefore, I will only add here that my stand on so-called invasive plants is based upon a lifetime of carefully documented observations ( in print, photos, and sound recordings) that I've made WHEREVER I've lived (the northeast, west, and southeast) or traveled. The natural world functions by the same laws everywhere.

My yard is well known for its abundance of wildlife species of every sort, and the fact is that it contains a mix of native and nonnative plants (including so-called invasives) that obviously support all of the critters extremely well. As I've now lived in this location for over 35 years, it provides valid proof of the value of a mixed landscape. And here's what is perhaps most fascinating of all: the majority of these creatures live in or right at the edge of the less than one-half acre I actively manage.

Rather than constantly interfering with what's going on in my yard, I have mostly allowed nature to take its course--something very few, if any, other people would do. Consequently, I have witnessed how the natural world truly works, and it's not as others portray it or want to believe.

(Edited by staff.)

hydrophilic

Disappointing to come across this article in 2021. Perhaps you are speaking from a local experience and extrapolating that experience onto the rest of the country. Birds and bees utilizing invasive plants does not make them a beneficial addition to the landscape. Native insects and native plants have co-evolved together over thousands of years and this has allowed insects to overcome specific plant defense mechanisms and form host plant relationships. Many insects can only reproduce on certain native plants. It will take invasive plants thousands of years to develop these relationships. A simple book to read on this topic is "Bringing Nature Home by Doug Tallamy".

As far as invasive plants being able to grow in areas which native plants cannot, I find that questionable. In many cases a blanket of invasive plants PREVENT native plants from emerging. By removing the invasives, native pioneer species can return on their own via seed bank, or with help. I've seen this many times myself. Cheatgrass in the west is a great example of a devastating invasive that displaces many natives which would otherwise have no problem growing. You can see a mule deer eating cheatgrass in the early spring and say to yourself "Hmmm, look that plant is being utilized by the deer and must be good for it" but in the real world a quick discussion with countless biologists who value research and in the field experience will fill you in on reality.

Even fruits from invasive plants have different nutritional compositions that may not prepare migratory animals adequately, etc. Certain birds target certain fruits. Western Bluebirds are dependent on mistletoe berries in the winter for example.

Invasive plants are good if you don't value the native species we currently have, which rely on the native plants they evolved with. I'm not saying we have to chase the past, ecosystems have always been in flux. The degree of change we are fostering right now is occurring too rapidly to allow adaptation for most of our wildlife. If we collectively decide we don't value our current suite of native species, fine, your article might make sense. I am not on that team, however.

Richard Dunbar

Mortice, These gov't agencies you have reverence for are all in on herbiciding the dickens out of the environment in order to 'help' it. This is how twisted in knots this issue has made the average environmentalist...not that the USDA is a shining beacon of environmentalism. Part of the USDA's job description has always been to assist agriculture in killing our native animals and native plants. Over the past few decades that mission has come to include non-native organisms, as well.

Additionally, eliminating all non-native plants is nothing more than a deer subsidy program that assists their multitudes to find the native plants hiding among the 'invaders'. The result, of course, will be no plants at all. Question: Is that the kind of environment you are hoping to achieve?

By the way, nothing says stream bank erosion control like an impenetrable stand of knotweed (which, I believe, helps the C Bay).

(Edited by staff.)

Mortice

You are wrong. "You could easily believe the dogma that these Asian plants “pushed out” native plants and took their place, but, simply put, you’d be wrong. Without an assessment of prior land use and the soil itself, you can’t possibly come to a reality-based conclusion about why certain plant species grow in these areas." This is very bold. Do tell, how has the Department of Conservation & Research done an amazing job to describe habitats and ecosystems and regions within Virginia? Do they come a mowed 1,000 acres, shrug their shoulders, and say, "I can't possibly know?" If non-native, invasive, ecologically devastating plants are "not that bad," is Japanese Knotweed "not that bad?" Is the hard work by the DWR, USDA, Forestry Department, DCR, Audubon Society - any society who actively studies and researches this top all for nothing? Without pulling the "appeal to authority strings," proven research is more valuable than an opinion article.

You should feel ashamed for promoting flagrant and environmentally harmful opinions.The comments guidelines states, "incorrect, fraudulent, or misleading content" and your article falls under this guideline.

Marlene

Dear Mortice, These agencies are responding to a situation that they view "in the moment". That is, they haven't paid attention to what had been happening for decades (otherwise, how could 1000! acres become covered in so-called invasive plants?). So yes, the folks working at the agencies do not have the full comprehension of the situation. I must point out that the "R" in DCR stands for Department of Conservation and Recreation, not "Research" as you wrote. Thus they do have a focus on people, which often guides how agencies deal with the environment. The DWR, formerly known as DGIF, is a prime example. Their focus until just recently has been about managing land for hunters, which is why the eastern part of the state is overpopulated with deer. USDA? This agency is all about making life easy for farmers and ranchers, killing off wolves out west, coyotes in the east, and the Black Vulture in Virginia. That hardly counts as conservation. Forestry Department? Again, until recently, their main focus has been the harvesting of trees as lumber for humans, not the conservation of them for the benefit of wildlife. As for Audubon and other environmental organizations, they fall prey to popular narratives, such as the much touted Doug Tallamy thesis that your yard must be 70 % native plants, which proved no such thing. Please see "Chickadee Chicanery" to learn the truth about this famous but incorrectly quoted study. https://indefenseofnature.blogspot.com/search/label/Carolina%20Chickadee.  I spend my time on this issue because of my genuine concern for our environment. I would hope folks would take the time to give my information consideration. I may not be published in this field, but I've spent my entire life observing nature and documenting what I've seen--in other words, doing research.  Sincerely,Marlene 

(Edited by staff.)

Marlene

Dear Sarah V,

It needs to be said that researchers suggesting research that supports the popular narrative at the moment are more likely to get grant money. And, as with anything that's paid for by someone wanting a particular result, they'll usually get that particular result. People are desperately trying to come up with things that "prove" so-called invasive plants are harmful, but so far, I've only seen nonsensical "proofs".

The suggestion that alien plants are somehow vastly different biologically from our native plants makes no sense in and of itself, but additionally, the arguments made with data don't make sense either. For example, let's take Autumn Olive, a plant people love to hate, so they say it's bad for migrating birds. But let's look at real facts.

Autumn Olive fruits mature in mid-to-late summer in Virginia and, because they are so popular with resident birds and mammals, they are long gone by the time many migrating birds are coming through. (If they aren't, there's not much local wildlife for some reason.) But let's say the fruits aren't gone. Are they "junk food" as I've seen them called? No. Birds, just like humans, require carbohydrates for quick energy to keep their body running. When carbs are broken down, they fuel the cells in bodies so they can function. Excess energy is stored as fat, which is exactly what migrating birds need to travel long distances. Most bird species need carbs THROUGHOUT their journey and need proteins and fats to build their muscles and grow feathers BEFORE migration, not during it. As for pollinators, they survive daily by eating SUGAR which is what they get from nectar. If the concentration of sugar is too low, they will feed more often or go to flowers that have a higher concentration of sugar. Pollen provides the primary source of protein for bees to build their bodies.

I have to ask why that forest was "an ocean of honeysuckle and barberry". Both of these plants require full sun to thrive, especially the barberry. If your description is accurate regarding these "invasives", then the forest could not have had much of a tree canopy. Why is that? Had the owner over-thinned his woods? Are the woods young, having been cleared in the past for timber or development? What's been done to the land in the past determines what happens in its future. There'a a problem here that has not been revealed which would explain the situation you feel you've "fixed".

The final question I would ask is whether the human fondness for spring ephemerals is more important than the year-around value of the honeysuckle and barberry to many forms of wildlife. Do you really need 30-plus acres to enjoy in the spring and then have nothing the rest of the year? It's your choice, of course, but what we're talking here is simply gardening for human enjoyment, not necessarily creating the best habitat for wildlife.

Sincerely,

The Author

Conservation Sense and Nonsense

To Sarah V regarding the use of herbicides to eradicate non-native plants. As a native plant advocate, you are probably familiar with Daniel Simberloff, the academic ecologist who is a strong supporter of invasion biology. Simberloff was the keynote speaker at the most recent conference of the California Native Plant Society in October 2020. He expressed his concern about the use of herbicides to kill non-native plants, although he shares your commitment to doing so.

The Executive Director of Cal-IPC and moderator of the conference asked Simberloff this question: “Dan, you mention the “futility” argument, but what about the notion that the cost in environmental damage (e.g, pesticide use and nontarget impacts) is too high for some well-established invaders?” Simberloff’s answer to this question was surprising and encouraging to critics of pesticide use to kill non-native species:

“Absolutely, it’s a huge problem, not only on non-target species, but also the fact that evolution of resistance leads to greater use of pesticides before they are useful and leads to greater impact on non-target species. I didn’t talk about this, but yes, of course the cost both economically and ecologically might be too great even if management eradication is feasible.

The Executive Director of Cal-IPC tried to save the day by portraying those who oppose pesticides as extremists, based on what he considers “unscientific” studies. But Simberloff wouldn’t take the bait. He wasn’t willing to dismiss the concerns about pesticides. Instead, Simberloff passed the buck:

“I’ll beg off on answering that question on grounds that I’m not a social scientist or psychologist. This is not my area of expertise. There is some reason for the extremists because Monsanto has sometimes lied to us and there have been problems associated with pesticides. I leave this question to policy scientists.”

The video of the Cal-IPC conference is available here: https://www.cal-ipc.org/2020-symposium-video/

Conservation Sense and Nonsense

In response to Sarah V: The birds are unlikely to have benefited from the removal of honeysuckle. Please read this study: Amanda D. Rodewald, et. al., “Does removal of invasives restore ecological networks? An experimental approach,” Biological Invasions, March 2015

The hypothesis of this study was that “invasion of urban habitats by exotic plants was the underlying mechanism driving changes in bird-plant networks.” The study tested this hypothesis by comparing forest plots dominated by honeysuckle with those in which honeysuckle had been removed and the surrounding forest habitat replicated. They measured nesting birds, nest predators, and nest survival.

They found that the lowest overall nest survival rates were found in the plots in which honeysuckle had been removed. In other words, “…removal of invasive honeysuckle from urban forests did not restore network structure to that of rural landscapes.” The authors concede, “This finding was not consistent with our original hypothesis that invasion of forests by the exotic Amur honeysuckle was responsible for the urban-associated changes in bird-plant networks.” They conclude, “The degree to which native communities can be restored following removal of exotic plants remains unclear.”

There are also studies about increased bird populations where honeysuckle is available. There are many similar studies that report that birds are served best by diverse gardens with longer blooming periods and diverse structure and habitat.

There is no scientific evidence that non-native plants are less nutritious than native plants and it makes little sense to make such a claim. All plants are native somewhere and birds migrate through the regions in which they are native. Obviously, the birds aren’t starving to death where those plants are native. All life is related and most plant families have chemically similar native and non-native members that provide the same nutrition to wildlife.

If you prefer native plants, by all means plant them. I don’t begrudge you your horticultural preferences. I ask only that you quit killing harmless plants on public land, particularly with dangerous pesticides. There is no scientific justification for such projects and wildlife would tell you that if they had a voice.

Sarah V

I’d be interested to know what the author proposes be done with the invasive species once they serve their “ecological benefit” at a denuded site?

I’ve read that just because a pollinator eats pollen or birds eat fruit of invasive plants does not equate to a nutritious meal for that animal. Sometimes the animals make-do with what’s available, but a diet with the fuel provided by the eaten fruits, pollens, seeds, etc. of invasives might not be enough to help a bird make its great migration south or help a pollinator survive the winter.

We recently helped a landowner clear his forest of invasive species. What began as an ocean of honeysuckle and barberry is now a sea of VA bluebells, spring beauties, trout lilies, and mayapples. Fortunately there seems to have been a seedbank of these natives (there was previously only 1/2 acre of them before the herbicide work; now it’s 30+ acres of these native flowers). We can’t allow invasive species to run amok for so long that the seeds of natives in the seedbank perish before conditions are adequate enough for the natives to germinate. Some seeds germinate after a century, but some can only last a few years. Without the seeds present, we must rely on wind, birds, and ourselves to repopulate a former invasive-infested site, which is expensive or is relying too much on luck.

Marlene

Dear Conservation Sense and Nonsense and still skeptical,

I am remiss in not having already thanked you for your much appreciated support of my work. I write about this contentious issue because I am so concerned about the damage being done to the environment by folks following a completely erroneous narrative. I hate arguing with people, but feel I have no choice but to provide the veracious account. People can't do what's right by the environment if they're misinformed.

Sincerely,

Marlene

Conservation Sense and Nonsense

In response to Carolyn's concern about garlic mustard: Here are three scientific studies about garlic mustard that are summarized by the lead author: “In six years of study, we have not been able to document any substantial effects by garlic mustard on other plant species, positive or negative. In fact, the best predictor of garlic mustard presence is high diversity of native plants. The most likely explanation for this fact is that all the species, garlic mustard included, are simply establishing in microsites favorable to plants in general. The same conditions that benefit native plant species also probably benefit non-native plant species.”

Davis MA, Anderson MD, Bock-Brownstein L, Staudenmaier A, Suliteanu M, Wareham A, and Dosch JJ. 2015. Little evidence of native and non-native species influencing one another’s abundance and distribution in the herb layer of an oak woodland. Journal of Vegetation Science 26:105-112.

Davis MA, MacMillen C, LeFevre-Lefy M, Dallavalle C, Kriegel N, Tyndel S, Martinez Y, Anderson MD, and Dosch JJ. 2014. Population and plant community dynamics involving garlic mustard (Alliaria petiolata) in a Minnesota Oak Woodland: a four year study. Journal of the Torrey Botanical Society 141: 205–216.

Davis MA, Colehour A, Daney J, Foster E, MacMillen C, Merrill E, O’Neil J, Pearson M, Whitney M, Anderson MD, and Dosch JJ. 2012. The population dynamics and ecological effects of garlic mustard, Alliaria petiolata, in a Minnesota oak woodland. American Midland Naturalist 168: 364-374.

Conservation Sense and Nonsense

In response to Carolyn’s botanist friend, who says, “And invasive-infested ecosystems are not likely to give way to native plant succession without management (i.e., herbicides).”

Herbicides are the most frequently used method of killing non-native plants, but using herbicides does NOT result in a native landscape. “Lessons learned from invasive plant control experiments: a systematic review and meta-analysis,” (K. Kettenring, Carrie Adams, Journal of Applied Ecology, March 2011) analyzed 355 studies published from 1960 to 2009 to determine which control efforts were most effective at eradicating the target plants and which method was most successful in restoring native plants. The analysis found that “More than 55% of the studies applied herbicide for invasive plant control.” Herbicides were most effective at reducing invasive plant cover, “but this was not accompanied by a substantial increase in native species,” because, “Impacts to native species can be greatest when programs involve herbicide application.” It’s not possible to kill non-native plants without simultaneously killing native plants and damaging the soil.

Sarah V

It’s possible to kill non-natives without killing native plants. Non-natives in our area display a great habit of greening up earlier than native species, thus one might treat the leaves (foliar spray) of a non-native without affecting the natives. There are also spot spraying techniques, where a person sprays individual plants without hitting all other plants in an area (kind of like people spraying individual dandelion plants in their lawn). There are preemergent herbicides that will stop seeds from sprouting, but have no effect on sprouted seedlings and mature individuals. Also, some evergreen species, such as Japanese honeysuckle, can be treated in the winter with a foliar application when all other plants are leafless. Finally, there are herbicides that only kill grasses or broadleaf plants. Applying herbicides is a science, involving the correct chemicals paired with correct timing. Sure, there might be some collateral damage to immediate native individuals or seeds, but licensed herbicide applicators should not be utilizing herbicides willy-nilly, such as applying an herbicide where no invasives are present or spraying on windy days or using an herbicide that disperses in water next to a stream). At least in my state, they are required to attend trainings every year for credits, ensuring they are kept abreast of new technology and regulations.

Sarah V

Granted, I think using herbicides to kill invasive species is a more justified need in natural landscapes than for using them to kill weeds in farm fields or in lawns.

Conservation Sense and Nonsense

In reply to Carolyn: Here are three scientific studies about garlic mustard that are summarized by the lead author: “In six years of study, we have not been able to document any substantial effects by garlic mustard on other plant species, positive or negative. In fact, the best predictor of garlic mustard presence is high diversity of native plants. The most likely explanation for this fact is that all the species, garlic mustard included, are simply establishing in microsites favorable to plants in general. The same conditions that benefit native plant species also probably benefit non-native plant species.”

Davis MA, Anderson MD, Bock-Brownstein L, Staudenmaier A, Suliteanu M, Wareham A, and Dosch JJ. 2015. Little evidence of native and non-native species influencing one another’s abundance and distribution in the herb layer of an oak woodland. Journal of Vegetation Science 26:105-112. PDF

Davis MA, MacMillen C, LeFevre-Lefy M, Dallavalle C, Kriegel N, Tyndel S, Martinez Y, Anderson MD, and Dosch JJ. 2014. Population and plant community dynamics involving garlic

mustard (Alliaria petiolata) in a Minnesota Oak Woodland: a four year study. Journal of the Torrey Botanical Society 141: 205–216. PDF

Davis MA, Colehour A, Daney J, Foster E, MacMillen C, Merrill E, O’Neil J, Pearson M, Whitney M, Anderson MD, and Dosch JJ. 2012. The population dynamics and ecological effects of garlic mustard, Alliaria petiolata, in a Minnesota oak woodland. American Midland Naturalist 168: 364-374. PDF

Carolyn

I'm someone who spends a lot of time getting rid of exotic invasives so that native plants have a chance to grow, and I have a different perspective than the author.

The author writes that once invasives move in and rehabilitate poor soil, natives can then reestablish themselves and thrive. I can’t help but wonder how that can happen in a forest that is completely overgrown with garlic mustard. Some sections of my woods are so thick with young autumn olives that you can’t walk through them. It’s hard to see how natives can establish themselves there without intervention.

The author cites no studies or data backing up her assertions beyond her own longterm observations. I have also made longterm observations and conclude that exotic invasives are pushing out many beneficial native species.

I showed the article to a friend who works professionally as a plant biologist and monitors plant communities for a living, and here’s what he had to say: “While I do feel that most invasive plants are not entirely without ecological value, it's another thing to go where this author has gone. She knows enough to make arguments that will sound somewhat reasonable to many, but not enough to reach the correct conclusions. It's certainly true that land use (or abuse) is part of the problem, but invasives are taking over in remote natural areas as well. And invasive-infested ecosystems are not likely to give way to native plant succession without management (i.e., herbicides). In a patch of forest where exotic invasives dominate, the overall ecological value/function of the patch is greatly reduced; studies have repeatedly shown that non-native plants generally provide less value/function and are completely useless to the many specialized insects that rely solely on some subset of the native flora for their existence. Her assertion that ‘native pioneer plant species are few in the Piedmont region of Virginia’ is just nonsense.”

Marlene

Dear Carolyn and your friend, the plant biologist,

I never said you couldn't do an intervention, but it's beyond me why people have so readily bought into the idea that poisoning the environment with pesticides is better than allowing plants to grow that DO create wildlife habitat. And if you remove plants physically, you are setting the biological-succession clock back by re-disturbing the soil. The question you should ask yourself is this: What are you trying to accomplish? People have been misled into thinking EVERY native insect needs a native plant to live its life, but that simply is not true. Doug Tallamy's focus is on caterpillars and sawfly larvae, but these organisms are not the only critters in the world nor even the most important ones. As a biologist, he should know better than to suggest that particular organisms are more valuable to the ecosystem than others. Your Autumn Olives, if allowed to grow, can feed an abundance of pollinators, birds, and mammals. Don't you care about them, too?

Plants provide information to people knowledgeable about them. If your woods are full of Autumn Olive and Garlic Mustard, there's a reason for it, which I can't address without personally seeing the state of your woods because what I've found over decades of talking with people about their properties is that they tend to not see them accurately. For example, in actuality, "invasives" line the edge of the woods rather than being throughout them, or if they are well into the "woods", the woods are so sparse that there's no tree canopy to shade them out. Plants don't grow in a vacuum; they can only grow where the physical conditions suit them.

You've concluded "that exotic invasives are pushing out many beneficial native species", but the reality must be you had no understory to begin with. Two plants cannot occupy the same space, so if Autumn Olives are coming up "everywhere", they are coming up where no shrubs or trees already were growing. Of course, there can be plant competition, but that's going to happen among native plants as well.

In a world of 7.9 billion people, I'd like to know where remote natural areas exist for "invasive" plants to take over. Even if your friend is suggesting that "natural" equates to untouched by human hands, those areas have been touched by manmade climate change.

He also asserts that "invasive-infested ecosystems are not likely to give way to native plant succession without management (i.e., herbicides)", but why should that be the case? Succession is succession, whether the plants involved are native or nonnative. We're talking about a natural phenomenon.

When the biologist says: "In a patch of forest where exotic invasives dominate, the overall ecological value/function of the patch is greatly reduced; studies have repeatedly shown that non-native plants generally provide less value/function and are completely useless to the many specialized insects that rely solely on some subset of the native flora for their existence." Again, I have to ask, why do people think every single plant needs to feed specialized insects? Yes, you can say nonnative plants "provide less value/function" for specialized insects, but it's wrong to claim this is true regarding the big picture as many of these plants are, in point of fact, useful for the overall diversity of life forms people should be trying to assist. My yard consists of a mix of native and nonnative plants and teems with wildlife species, so much so that it has been featured on Virginia PBS stations twice.

Lastly, your biologist friend claims my "assertion that ‘native pioneer plant species are few in the Piedmont region of Virginia’ is just nonsense.” If that's so, he should provide a long listing of pioneer species beyond those I listed instead of making an accusation that is itself nonsense. I've lived in Virginia for 45 years and know the landscape well. 

Sincerely,

Marlene

(Edited by staff.)

Conservation Sense and Nonsense

Thanks to JRD for asking for studies that document the value of non-native plants to wildlife. Here are a few:

• Arthur M. Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110, 413-433, 2003. Based on 40 years of walking his research plots in California, Professor Shapiro (UC Davis) reports that native plants are not more useful to California butterflies than non-native plants and a few butterfly species are now dependent on a non-native plant species.

• Dov Sax. “Equal diversity in disparate species assemblages: a comparison of native and exotic woodlands in California,” Global Ecology and Biogeography, 11, 49-52, 2002. Professor Dov Sax (Brown University) compared insects living in the leaf litter of the non-native eucalyptus forest with those living in the native oak-bay woodland in Berkeley, California. He found significantly more species of insects in the leaf litter of the eucalyptus forest in the spring and equal numbers in the fall. Professor Sax also reports the results of many similar studies all over the world that reach the same conclusion.

• Tallamy, Doug, “Flipping the Paradigm: Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011. A graduate student working under Doug Tallamy’s direction compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally. After two years of measurements the student found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season. The most important result, however, was that there was no statistical difference in the amount of damage on either landscape type. That is, no evidence of insect preferences of native vegetation was found by a study directed by Doug Tallamy.

There are hundreds more such studies and six books published about the value of non-native plants to wildlife and related considerations in the debate about novel ecosystems.

1. Fred Pearce, The New Wild, Beacon Press, April 2015

2. Emma Marris, Rambunctious Garden, Bloomsbury, 2011

3. Ken Thompson, Where do camels belong?, Greystone Books, 2014

4. Mark Davis, Invasion Biology, Oxford University Press, 2009

5. Chris Thomas, Inheritors of the Earth, Public Affairs, 2017

6. Tao Orion, Beyond the War on Invasive Species, Chelsea Green, 2015

I have read the books and studies of Doug Tallamy. He exaggerates specialization of insects and underestimates the speed of adaptation and evolution. All life on Earth is related. A specialized insect that is confined to one or two families of plants has many alternatives for its host plant because there are hundreds—sometimes thousands—of species in the family that are chemically similar. There are both native and non-native plant species in most plant families. For example, monarch butterflies in California prefer non-native tropical milkweed to native species of milkweed as their host plant (according to a study conducted at UC Davis). That is typical of the transitions that insects make when new plants are introduced.

Richard Dunbar

"Massive destruction by invasive terrestrial plants." Why is hysteria and hyperbole over these plants always the default position of native plant people?

We currently have a situation where in the eastern half of the country, at least, deer have literally and completely changed the nature of mans' leftover lands (areas man no longer uses after completely using them up ahead of deer inundation). But, rather than native plant people focusing on their own state wildlife agencies to rectify this problem (adequately controlling deer numbers that are eating all the native plants), they, instead, blame the non-native plant for all the environmental damage. Why is that? This isn't rocket science.

By the way, Tallamy calls these plants bio-pollution. Note to backpack-sprayer-clad neo-environmentalist: Do not fall into the trap that pesticides are better for the environment than these plants. That is not the road to environmental salvation.   

(Edited by staff.)

still skeptical

What a refreshing article! The war on “invasive” plants has such intense support from public policy and public funds that people lose sight of the services non-natives perform. We should be thankful non-natives volunteer to brighten degraded fields and roadsides, as well as to provide food and cover for wildlife. Only time will tell what plants truly “belong here.” We will see what thrives in our radically changed environment under a radically changed climate.

still skeptical

What a refreshing article! The war on “invasive” plants has such intense support from public policy and public funds that people lose sight of the services non-natives perform. We should be thankful non-natives volunteer to brighten degraded fields and roadsides, as well as to provide food and cover for wildlife. Only time will tell what plants truly “belong here.” We will see what thrives in our radically changed environment under a radically changed climate.

Marlene

Dear MCF, DStuart, and MollieKing:

Thank you for sharing your thoughts so I can address them.

I'm not sure why folks always assume I haven't read Doug Tallamy's books or research. In fact, I was talking about nature-friendly gardening long before he was, having appeared on Virginia Public Television to discuss my yard in 1994. My book came out in 2006, a year before Bringing Nature Home. I was given an advance copy of Bringing Nature Home to write a review of it, and what I found was a book filled with the usual  misinformation about "invasive" plants, along with erroneous "facts", such as that no native predator fed on nonnative insects. It told me this man might know about leaf-eating insects, but as is the case with most scientists (due to their in-depth specialization) he didn't know much about what is actually taking place "out there". Rather than publicly panning his book, I thought it better (and more considerate) to inform Timber Press of the situation in, if I recall correctly, a 2-page listing of errors (which was just the tip of the iceberg!).

I'm aware of scientific studies that claim our pollinators are somehow unable to get the nutrition they need from alien plants, and I'm also aware that there is plenty of--I hate to use the expression, but it's true--junk science being published and then publicized as if it's valid. In fact, the Tallamy, et al. chickadee study that everyone references as proving birds need 70% native plants is one of them. Please read "Chickadee Chicanery" (link below) to see what I'm talking about. https://indefenseofnature.blogspot.com/search/label/Carolina%20Chickadee

Then there's the issue of climate change. Many animals, such as bees and butterflies, are coming out of hibernation LONG BEFORE our native plants start blooming. Even if the food value of alien plants was inferior (which I don't believe), I certainly would rather an animal survive by getting something to keep it going rather than die because there's NO nutrition anywhere.

Lastly, people claim alien plants invade natural areas, but their eyes are closed to the reality of these situations. "Invasives" tend to be sun-loving, and thus simply can't invade a forest unless it's been over-thinned (common in many properties managed for timber, or as a result of drought or--as in Shenandoah National Park--ice storms),  or a trail has been made through the forest allowing sunlight to reach the ground. Of course, if the forest borders a field that had previously been part of a farm (the case of a local "natural" area where I live), it will have "invasives" at its out edge. I've never seen an intact, healthy forest invaded. Mainly what you'd see if you really inspected each situation are human-impacted forests that serve to invite aliens in, rather than alien plants taking over. 

Sincerely,

Marlene 

JRD

So I have heard this line of thinking before, but are there any studies you can point me to that back this up? I see a lot of areas filled up with monocultures of invasives and have a hard time seeing how this is beneficial.

Marlene

Dear JRD,

I'm sorry, I didn't see your comment at the site last evening when I replied to the other 3 folks.

I'd like to ask you a question, please: Do you see areas of native-plant monocultures as beneficial? I live not far from a dam surrounded by forest where the deer overpopulation has created monocultures of Spicebush and Pawpaw because they don't eat these plants. A diversity of plant life is always the better situation for supporting a diversity of animal life, so I don't see native-plant monocultures as beneficial, yet I never hear anyone discuss these areas as being problematic. They are no different than alien-plant monocultures.

I can assure you that over time, after the soil has been improved by alien-plant pioneers, native plants will show up. When I moved into my house 35 years ago, the yard had been scraped bare of its topsoil and the remaining gray subsoil looked for all the world like the surface of The Moon! But many, many native plants have moved onto my property of their own accord and it's a thriving wildlife habitat (which is how I know about this subject so well). If you walk down the road I live on, you know when you've reached my property because it's the only one from which wildlife sounds galore (birds, frogs in season, insects) emanate.

The narrative regarding "invasive" plants is wrong, as I know from decades of personal experience and recorded observations. Please visit my website (In Defense of Nature) for many of my published articles and blog posts. www.InDefenseofNature.com

I appreciate your interest and willingness to look deeper into the subject.

Sincerely,

Marlene

MollieKing

While it's true that roadsides, fields compacted and denuded by heavy machinery and poor agricultural practices, and eroding hillsides all pose serious challenges - and some non-natives are "successful" as pioneer plants in such areas, I can't agree with your conclusions. Show me any place where kudzu, autumn olive, callery pear, English ivy, Japanese honeysuckle, Japanese stiltgrass, barberry, or multiflora rose stabilized a disturbed area then retreated as native plants regained a foothold? On the contrary, these alien species generally gain a foothold in waste areas then encroach into natural (native) areas that are doing just fine and, yes, crowd out natives. Look at any of the woods around populated areas and you'll see acres of stiltgrass and garlic mustard that outcompete the woodland natives. Maybe an argument can be made less aggressive non-natives that blend, and have naturalized into the landscape without taking over during the past 400 years. But I still think the argument for eliminating non-native invasives and gardening with natives is a strong one. (The same goes for other countries, where some of our North American species have become invasive.)

DStuart

The scientific data shows massive destruction by invasive terrestrial plants. A good place to start understanding this by reading Douglas W. Tallamy's book, "Bringing Nature Home." Then go to the studies. Just because pollinators 'use' an invasive for nectar doesn't mean it's getting the nutrition it needs from that plant. I've worked for 8 years as an award winning habitat restoration volunteer and let me tell you, the plants on the MD Inv. Species Council List make a huge negative impact on previously pristine native woodlands. I've met some "invasive" deniers--I hope when they go deep and learn what birds and critters really need to eat/live/raise their young, they'll understand the problem. People weed their yards, their gardens--forests have to be maintained as well, especially those surrounded by population centers.

MCF

I have a 1/4 acre yard planted in native plants, and I can say, there is no comparison regarding

the diversity of bees and other pollinators, as well as birds, that I see in my yard now compared to the days when I had a typical suburban backyard. Over the years I have seen former forests whose trees have been totally toppled by non-native bittersweet, and areas inundated with garlic mustard and stiltgrass, that used to have prolific populations of spring ephemerals and other native herbaceous plants. If you enjoy your lesser celandine and autumn olive, go for it, but please keep them away from the natural areas I enjoy. Maybe you should read Doug Tallamy's books for the science that explores the limits in wildlife value of non-native plants., compared to native plants.

Marlene

Dear Oceanadrian:

Thank you so much for your comment. I would certainly be able to write a follow-up article listing the wildlife value of "invasive" plants, if the Bay Journal would like me to do so.

Why don't you think Lesser Celandine is useful? Just this past March 30, I watched Spring Azures (very small blue butterflies) going to the Lesser Celandine blooms in my front yard. I've also recorded other pollinators, such as bumblebees and carpenter bees feeding there, and as you know, pollinators are in trouble. In fact, I doubt any so-called invasive plant is not useful to some kinds of  wildlife.

I deeply appreciate your interest!

Sincerely,

Marlene

Oceanadrian

A very interesting article. I had never thought of Autumn Olive as being valuable. Surely not every invasive is useful (e.g. Lesser Celandine) so a follow up article listing those that are beneficial and those that are not would be very useful.

Conservation Sense and Nonsense

Thanks to the Bay Journal for publishing this excellent article about non-native plants that are capable of tolerating the changes human activities have made in nature. The success of non-native plants is a symptom of changes in the environment, not the cause. As this article explains, non-native plants prevent erosion of barren ground and restore damaged soil in the short-term. In the long-term non-native plants that are adapted to changes in the climate will be the landscape of the future. When the climate changes, the vegetation changes. This natural sequence of events has been demonstrated repeatedly for millions of years. When we try to eradicate non-native plants with herbicide, we are exacerbating the damage that has created opportunities for plants that can tolerate disturbance.

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