Invasive Species Aren’t the Actual Problem, They’re Merely a Symptom

Climate change, habitat destruction, and changes in land use and management contribute to their proliferation

From California to South Africa, New York to New Zealand, invasive species seem to be everywhere, their populations expanding and threatening ecological integrity around the world. A 1998 Princeton University study found that invasive species are the second greatest threat to global biological diversity. In 2011, the International Union for Conservation of Nature, the world’s oldest and largest global environmental organization, warned that invasive species wreak havoc on economies and ecosystems. Organizations such as the National Wildlife Federation and the National Audubon Society consider invasive species to be serious impediments to healthy wildlife habitat and the survival of endangered species. And government agencies, including the US Forest Service and Bureau of Land Management, blame invasive species for losses and permanent damage to the health of natural plant communities.

purple loosestrifePhoto by Jack McLane/FlickrPurple loosestrife (Lythrum salicaria), an invasive perennial plant is spreading rapidly in North American wetlands, shorelines, and roadside ditches. The choices we make on a daily basis—the ways we procure food, shelter, water, medicine, and transportation—are the major drivers of contemporary changes in ecosystem structure and function.

Species invasions are also costly. According to The Nature Conservancy, worldwide spending on invasive species totals $1.4 trillion every year, equal to 5 percent of the global economy. The United States alone spends $137 billion annually to contend with them. The National Invasive Species Council holds invasive species accountable for “unemployment, damaged goods and equipment, power failures, environmental degradation, increased rates and severity of natural disasters, disease epidemics, and even lost lives.”

Given the apparent threats posed by invasive species, it makes sense that their eradication has become a central organizing principle of the practice of restoration. After all, if they are perceived as degrading ecosystems, then the practice of restoration as assisting in the repair of degraded ecosystems should focus on their elimination. I know that people who work in restoration care deeply about the loss of habitats, loss of ecological function, and declining biodiversity that are readily apparent in seemingly every ecosystem on Earth. Invasive species in many cases are part of this trend, and while I agree that invasive species are less ideal than the diverse and robust native flora and fauna they appear to dominate and replace, invasive species themselves aren’t the actual problem; they are merely a symptom. I remove invasive species on my own property and in my own design work, but always in the context of creating something greater, more robust, diverse, and resilient than what was there before, and I have never considered using herbicides to manage them. As individuals, we have to take responsibility for the land. We have to draw the line.

Herbicides are favored as a restoration tool because they represent a relatively cheap, readily available, and supposedly benign method of killing certain plants and favoring others. Herbicides can be applied in small, targeted amounts, ridding the site of unwanted species with relatively little disturbance (at least visually) compared to seemingly more destructive eradication tools like bulldozers and tractor-mounted mowers. Planes, helicopters, and people with backpack-mounted spray tanks can apply herbicide in remote locations that are not easily accessed by other eradication equipment. Herbicide application can be selective, as it is easily applied to certain plants and not others on a small scale. Working with a weed whacker or machete does not allow for the same careful treatment. In some cases, such as the Lane County project I worked on and others I visited, herbicides are used on a larger scale in the hopes that the site can start with a “clean slate,” leaving the desired native vegetation more or less free from the competition expected from rampantly growing invasive species.

controlled burnPhoto by Colby Hawkinson/USFWSA biologist lights a controlled burn to maintain wildlife habitat in a brackish marsh in Eastern Neck National Wildlife Refuge, Maryland.Fire is one of many tools biologists use to promote native plants and exclude invasive ones.

I understand the need for cheap and straightforward vegetation management strategies, especially on a large scale. I’ve spent many a sweaty hour at the helm of a well-sharpened hoe. But the idea that herbicides are considered a necessary part of restoring an ecosystem didn’t sit right with me. If organic farmers can grow nonnative plants like broccoli, potatoes, and turnips without the use of chemical pesticides, why should native plants need them, I wondered? I assumed that native plants and animals are supposedly more suited to local conditions than nonnative ones, so it seemed to me that they should be easier to establish and maintain than those crops commonly grown in a farm setting.

As I considered how to curb the rampant growth of invasive species without chemical intervention on the site I was hired to restore by the Lane County Department of Public Works in Oregon’s Willamette Valley, I turned to organic farming for possible solutions. At the first organic farm I worked on, we’d used backpack-mounted propane torches for spot-burning the carrot beds. Carrots take a couple of weeks to germinate, and many weeds emerge sooner, impeding their growth. With a few well-timed passes of the torch, I could drastically reduce the number of weeds competing with the carrots, making successive weeding more efficient.

I reasoned that a similar approach could be taken at this wetland restoration site—eliminate the early germinating and rapidly spreading invasive plants, and make room for more slowly emerging desirable native species. Although backpack burning is standard in organic farming, it had not been used as a restoration tool in the Willamette Valley. Still, my supervisors were willing to let me try it.

We found that spot burning worked successfully to eliminate populations of rattail fescue and worked reasonably well on false dandelion and the pennyroyal that grew along the pond margins. We sowed seeds of native tufted hairgrass and American sloughgrass into the burned patches, which germinated readily in the moist soil. This approach seemed to work well, at least as well as spot spraying.

However, as I stood out in the middle of the site one cool, windless morning in April, eight months into the project, with my propane torch in hand, I burned a native spotted frog—an amphibian recently listed as a threatened species in Oregon—that had been hiding in a patch of the invasive rattail fescue. Its skin was badly charred, and it died soon after. I couldn’t help but feel that my actions were not serving to enhance the ecosystem in the best way possible. I was glad to keep herbicides out of the watershed, but there had to be better ways to improve ecological functionality and habitat value than by removing certain plants, especially if their eradication caused harm to the very creatures that were supposed to benefit from restoration of the land. This was the same problem I had with herbicides: No matter what, the ends justify the means. Spot burning invasive plants was supposed to be a tool that would create more and better habitat for native frogs and plenty of other creatures over time. Did burning a few frogs along the way matter in the context of the long-term goal of creating a wetland ecosystem on the site?

These questions haunted me as I continued to work on the project. I began stamping around in the patches of rattail fescue and pennyroyal, hoping to scare the frogs out of their habitat before I ignited the torch. But then I realized that the patches were everywhere and that the pennyroyal, rattail fescue, and false dandelion were serving other valuable roles in the ecosystem of the project site. The false dandelion and pennyroyal were covered with honeybees and native pollinators when they bloomed, and these too fell as ashes under my torch, leaving the pollinators to forage elsewhere.

I realized that even though I was using a technique borrowed from organic farming instead of herbicide-based eradication, I was still working within a paradigm that viewed invasive species as threats to ecological health when my assessment of reality on the ground demonstrated the opposite. The invasive species were serving ecological functions—the bees didn’t appear to mind that the nectar they sipped came from a flower that originated in Europe nor did the frogs seem to care that the low-growing thatch of rattail fescue hailed from the same region. They may have preferred native vegetation, but it was hard to tell, especially since native plants were not thriving and certain invasive species were. Was the success of the invasive species based on the fact that they were supposedly more aggressive or more competitive, or were other factors contributing to their proliferation? And were the pollinators and frogs just making do with what was available, or were their pollination activities reflective of a changed and changing ecosystem? I realized that in order to develop a truly holistic approach to restoration, one in which the ends and the means were justified by enhancing ecological integrity every step of the way, I had to take a step back and look at the bigger picture, taking what ecologist H. T. Odum called a “macroscopic” view of observed ecological phenomena.

Orange, Ice PlantPhoto by miheco/FlickrOrange and red ice plant which is now considered an invasive species in California. The fact is that invasive species were serving ecological functions — the bees didn’t appear to mind that the nectar they sipped came from a flower that originated in Europe nor did the frogs seem to care that the low-growing thatch of rattail fescue hailed from the same region.

So I decided to zoom out from the frogs, the grasses, and the ponds and look at the site in terms of its own history, as well as how it was situated within the changing dynamics of the surrounding ecosystem. The 64-acre site had been farmed for more than fifty years and probably had been a wetland within its long history, prior to the construction of flood control dams and the massive wetland draining efforts throughout the late nineteenth and early twentieth centuries that enabled the development of tillage-based agriculture in the Willamette Valley. From wetland to farm to wetland again, each of these transformations engendered ecological changes, some more obvious than others, in soil characteristics, species assemblages, water flows, and other dynamics.

The plan to restore the site to wetland characteristics had called for the removal of 30,000 dump truck loads of soil—enough to fill a football stadium 330 feet deep—in order to reach the water table and create year-round standing water. Bulldozers, scrapers, excavators, and dump trucks rolled over the site day after day, for months on end, digging, shaping, and compacting the soil. The site was sprayed and sprayed again. Thousands of pounds of native seeds were broadcast across the site, and yet invasive species still thrived.

In fact, the treatment of the site during the course of its restoration, as well as its recent history as a grass seed farm, created the niches for invasive species to thrive. The soil excavated from the site was mostly organic matter–rich topsoil that was trucked away to cap the adjacent, nearly full landfill. Wide swathes of false dandelion radiated out from the imprints of the tire tracks in the bare clay subsoil, and pennyroyal spread along the wet margins of the newly excavated ponds where nothing else grew. False dandelion, with a taproot like its more famous cousin, will over time break up the most compacted soils. Pennyroyal, though it forms dense mats, attracts pollinators, which in turn feed birds, amphibians, and fish, each in their way contributing to the development and diversification of the emerging ecosystem.

And though thousands of dollars’ worth of native seeds were purchased and sown on the site, relatively little germinated. Native wetland plants are not adapted to bulldozer tracks and compacted clay subsoil. Restoration in this case entailed fabricating a novel ecosystem, so from an objective standpoint, the proliferation of novel species could be considered an expected outcome. However, the restoration plan was based on the concept that once the physical environment (in the form of a wetland) was created, and the pesky “weeds” removed, native species would flourish on the site. Were the native plants we chose adapted to early-, mid-, or late-succession wetlands? As far as I could tell, we were mixing plants from all different parts of the ecosystem succession spectrum, hoping that some of them would take root. I suggested that we choose seeds from native plants that were similar in form and habit to the invasive species, reasoning that the invasive species were filling a functional role in the ecosystem on some level and that if we wanted native species to flourish instead, we should mimic the characteristics of the invaders.

We decided to give it a try. We chose native self-heal and mat-forming checker mallow to mimic the pennyroyal. We sowed tufted hairgrass, American sloughgrass, and various sedges to fill the void of the rattail fescue. We planted yampah tubers and bulbs of native lilies including camas, narrowleaf onion, and harvest lily to mimic the decompacting action of the false dandelion’s deep taproots. In the spring, the wetland bloomed with flowers, and pale green grasses and sedges sparkled on the pond margins.

In order to stock the site with the native plant species we were looking for, we scouted the region for robust populations of native plant seeds, bulbs, and tubers. We harvested 30,000 camas bulbs from a location where a new road was being constructed. We collected wapato tubers from a local farmer who happily plowed up the mucky ground where they grew in the hopes of expanding his grass seed operation. We picked seeds from the endangered Bradshaw’s lomatium growing at the landfill and Oregon gumweed, tule, and water plantain from roadside ditches. Mule’s ears and tarweed grew next to the interstate, their full seed heads whipped back and forth by passing traffic.

It was difficult to reconcile the irony that we found the largest stands of native seeds, tubers, and bulbs—which were so critical to “restore” to the wetland site—from places where they were obviously unwanted or unutilized. As I thought more deeply about this conundrum, I realized that it was the heart of the issue. The native plants, which have been, and continue to be, cultivated and valued as food, medicine, and fiber crops by the indigenous people of our area, are marginalized by most everyone else. If restoration of native species and habitats is critical enough to warrant the use of herbicides to maintain and enhance their populations, then why doesn’t our culture value these organisms and the ecosystems where they thrive? Native plants and animals should be valued in agricultural, forestry, mining, and ranching operations; shopping malls, golf courses, and power plants should be habitats and havens. But, for the most part, this isn’t the case. Restoration focuses on native species in certain isolated contexts—like the 64-acre wetland where I worked—but not in others. It typically occurs in so-called natural areas that are artificially separated from the majority of “productive” ecosystems where less than optimum ecological outcomes are considered normal.

It occurred to me that if we are to restore and enhance populations of native species, then we must restore our sense of belonging within the ecosystems that we depend upon. We must reimagine restoration as a practice that takes place in all ecosystems, especially those from which we derive our daily needs. Ecosystems should be restored and enriched by every action we take and decision we make, including the methods we use to procure our food, shelter, water, and other necessities of daily life. Restoration should be designed into every facet of our lives.

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