The War on Invasive Species. Part I: The Power of Language

Today GardenRant welcomes back garden ecologist Nathan Lambstrom, in Part I of a three-part series discussing invasive species rhetoric, and the negative effects powerful war metaphors have had on the perception and management of exotic and invasive plant species in our gardens and greater ecoregions.  The series will explore the roots of this language; the tangible harm it can cause; and the future of invasive management. We hope you’ll follow along and offer your thoughts in comments as he begins with the origin story of terms that have become internationally commonplace. – MW

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English ivy was the first plant I learned to hate.

As an undergrad, my first environmental studies class included a field excursion to a local woodland as part of our unit on invasive species. The forest was small, fragmented, and surrounded by centuries of development in the form of agriculture, and subsequent suburban housing. It was also home to a thriving population of English ivy, Hedera helix.

We were taught that this plant, like many other ‘exotic’ plant species, was rampant and destructive, killing native plants and dragging down trees. Fired up by this new way of categorizing the world, my classmates and I volunteered to remove English ivy on weekends. We ripped it out with abandon, filling garbage bags with piles of it and its distinctive goose-foot leaves.

We took a perverse pleasure in pointing out invasive plants to friends, chastising local shop owners for selling them, and making sure everyone saw this plant as a villain. There was never any plan to restore native plants after the English ivy removal, and no discussion of the conditions that led to its thriving in the first place. We just knew we had found an enemy to blame for our degraded forests.

From that point on, I spent many years seeing and attempting to heal wounds in the landscape – horrible invaders like tree of heaven dominating post-industrial streambanks (Ailanthus altissima), purple loosestrife destroying post-agricultural wetlands (Lythrum salicaria), and garlic mustard killing natives in fragmented woodlands (Alliaria petiolata).

But the more time I spent working with these plants, studying them, and ‘battling’ them, the more I also started to question the simplistic narrative of marauding monsters destroying our native landscapes. There was a more nuanced story than ‘good vs. evil’ unfolding around me, and after graduation in the summer of 2008, I started to pay attention to it.

A Weedy – But Successful — Life Strategy

That summer, I monitored the spread of garlic mustard for a land trust. My job was to walk mile-long transects and record each occurrence so we knew where to send fresh volunteers to yank it and stuff it into plastic garbage bags.

But to my surprise, I began to notice that the seemingly ubiquitous, destructive patches of garlic mustard began to fade the farther I got from areas of human influence.

Roadsides and trailhead parking lots? Plenty of garlic mustard. Farm fields that had been abandoned in the last few decades? You bet. But deeper in the woods where there was less foot traffic, vehicle traffic, or consistent human influence, I found less and less garlic mustard – and instead found myself crawling through impenetrable tangles of rhododendron and mountain laurel.

At first it seemed like the plant might be starting its invasion from those roadside patches; but the more I learned about plant ecology it became more difficult to see this plant simply as a malicious invader.

Ruderals – The Opportunists

Garlic mustard is a biennial: it forms leaves and taproot in year one, then draws on stored energy to form a tall flowering shoot in year two (the same strategy employed by carrots, foxgloves, and hollyhocks). After flowering in the second year, all energy in the taproot is spent and the plant dies.

Short-lived plants like this – mostly biennials and annuals – are called ‘ruderals.’ Ruderals guarantee the survival of their species by employing the ‘live fast, die young’ principle. Though the parent will live for a relatively short time of one to three years, it will produce abundant seeds that germinate easily when the conditions are right.

Anyone growing vegetables is familiar with ruderals. Ruderals want a low stress environment (ample sunlight, water, & nutrition), and plenty of disturbance, usually in the form of soil agitation and removal of other plants.

When we farm or grow vegetables, we create the perfect low stress environment to favor ruderals, which comprise many of our agricultural weeds. Plants like chickweed and lamb’s quarters will germinate, grow, flower, and set seed rapidly, leaving plenty of seeds in the soil for the next generation.

What I was observing in garlic mustard populations was effectively the same strategy employed in a different environment. As a short-lived plant, it was simply taking advantage of openings created by us.

When we make roads or farms or trailhead parking lots, we create large disturbances which take several decades to recover. As long as resources are adequate, garlic mustard, and other ruderal plants (whether native or not), grow and reproduce quickly following these disturbances. This means those plants are dependent on disturbance for their continued presence in the landscape. As time without disturbance increases, long-lived plants more tolerant of stress will increase as conditions become less favorable for ruderals.

And what is an excellent form of disturbance? Pulling garlic mustard. Every plant we pulled disturbed the soil and created perfect conditions for germination of hundreds of garlic mustard seeds. By pulling it without planting something in its place, we were perpetuating its spread.

Language Matters

This simple observation piqued my curiosity. And the more I worked with invasive plants as an ecological restoration technician, and studied them as a graduate student, the more it seemed that the way we were discussing them was not reflecting ecological reality.

I had been taught to think of these plants as “exotic invaders” and “ecological monsters” that were destroying native plants and killing our ecosystems. Today in top media outlets they are described as “thugs” and “monsters” that can engage in “chemical warfare” and “do battle” with native plants. These may seem like harmless terms, but it’s worth noting that plants are not capable of acts of war.

We have spent so much time steeped in this language that we’ve lost sight of the fact that is a metaphor, and a very effective one, that shapes our perception of plant ecology and affects the way we respond to these plants in our landscapes.

This is language that leaves no room for nuance and is used to justify harmful actions in favor of eradication at all costs. It feels scientific and objective because it’s the language that has long been used by scientists studying these species, myself included, to communicate a complicated concept, but at its core is a subjective war metaphor intentionally crafted to grab attention.

Origins of a War Metaphor

How did we get these words if they’re not an accurate reflection of our observations?

The answer is Charles Elton, an English zoologist working during and after WWII who studied fluctuations in animal populations. During the war his work became of national importance in securing a fragile food supply and was used to manage agricultural pests like rats, mice, voles, and moles.

Following the war (and undoubtedly shaped by his own traumatic experiences under threat of German invasion) Elton published The Ecology of Invasions by Plants and Animals. Knowing that the world was still reeling, Elton used war metaphors to communicate what he considered the threat posed by species spreading rapidly outside their historically native ranges.

He laid out many of the foundational underpinnings of invasion biology and shaped much of our understanding of these occurrences. According to Elton (and this is the definition most commonly used by any entity determining invasiveness today) an invasive species is one that:

1) is introduced outside its native range;

2) is spreading rapidly; and,

3) is causing measurable harm.

This feels very tidy, but if you spend time considering plant behavior, you quickly see the edges are blurry.

How Do We Measure Invasiveness?

The question “what is the definition of an invasive species?” is similar to “what is the definition of a weed?” The short answer is, there isn’t a simple answer.

‘Weedy’ and ‘invasive,’ like ‘native’ and ‘non-native,’ are not biological categories, they are cultural-historical ones that reflect our attempts to categorize a chaotic and incredibly complex ecosystem. It may seem like we should be able to measure, in a scientific way, whether a plant is invasive or not, but it requires a great deal of subjective judgment, based on evidence, to determine invasiveness.

In other words, if you found yourself in an ecosystem you’d never seen before, there would be no way for you to determine which plants were invasive, because there would be no way to determine origins or harm. You could measure rate of spread, but you wouldn’t know whether it was a native plant behaving the way it evolved to behave in its ancestral home or an introduced plant running wild.

Similarly, harm is surprisingly difficult to quantify. You could observe that one plant replaces another over time by being more competitive, but you would still be left with the question of whether what you were seeing was ‘harmful,’ or simply the transition of an ecosystem to a further stage of succession.  Is the transition of an abandoned farm field to a closed forest a form of ‘harm’?

Defining Harm

Because these edges can be blurry, the definition of harm is often simplified as ‘economic harm’ – like agricultural losses or structural damage, or, increasingly, the cost to simply remove the species itself.

Quantifying the last of these can become troublingly circular. If we define ‘harm’ as merely the presence of an invasive species in an ecosystem where we don’t want it, then we’re relying only on its presence to justify its removal without documenting any causally linked damage. In other words, we’ve already made up our minds that it has to go just by virtue of its existing there.

Even within the contours of that three-part definition, we can see that certain things often called invasive should be excluded by the harm metric. It has become a popular assumption that anything ‘exotic’ (more accurately ‘introduced’) and thriving here without human assistance is invasive, but it is difficult to make a compelling case for the harm caused by plants such as dandelions or Queen Anne’s lace.

Conversely, it’s often assumed that invasive plants grow and behave differently than native plants; but many of us have seen Canada goldenrod spread rapidly to the detriment of other plants in a meadow. In many cases, the only thing distinguishing a competitive native plant from an evil invasive one is that the invasive one has evolutionary origins elsewhere.

That should not be enough to sustain it as a meaningful category.

A Shift in Perspective

After two decades working in field conservation, restoration ecology, and ecological horticulture, I’ve come to believe that using war metaphors to discuss invasive species has outlived its usefulness. From toxic chemicals sprayed to curiosity stifled, this unscientific and militaristic language has caused real harm in the way we talk about, think about, and deal with invasive species.  

Does rethinking how I talk about invasive plants mean that I don’t care about native plants? Absolutely not. Recognizing the more nuanced ecological reality of invasive plants in no way diminishes the importance of native plants, and has not stopped me from loving, promoting, and planting thousands of them every year.

Wild native plants form the backbone of our terrestrial food webs, and they have intrinsic value in their own right – as do all living creatures. Some of them are crucial for supporting the rare but important cases where insects have extremely restricted diets, like Karner blue butterfly larvae needing Lupinus perennis, or Andrena erigenae, a small native bee, needing Claytonia pollen to feed their larvae. However, caring deeply about native plants doesn’t require believing that non-native or even invasive plants are ecologically useless and evil.

When we approach our interactions with these species as if we were at war, we are likely to incur war-like consequences: collateral damage in the form of harm to our ecosystems and to ourselves.

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In Part II Lambstrom will discuss some of the real ecological and cultural harm that can be incurred by the most extreme forms of invasive rhetoric. Stay tuned!