Association of State Wetland Managers - Protecting the Nation's Wetlands.

For Peats Sake: Invasive or Evolutionary Ecology?

By Marla J. Stelk, Policy Analyst, ASWM

I have experienced first-hand the losing battle with invasive species. It’s a battle I fight every year just trying to stop the advancement of Asiatic Bittersweet which is killing almost every tree in the wooded area behind our back yard. I have seen the devastation that invasive species can wreck on  marlablog822141habitats, flora and fauna so it’s not a subject I take lightly. But in my efforts to understand the issues and practices involved in addressing the issue of invasive species, I continually find myself at odds with the overwhelmingly prevalent practice of rapid eradication – particularly with methods that employ toxic chemicals such as glyphosate or the introduction of new exotic species.

In trying to explain my consternation, my mind constantly evokes the analogy of those annoying pharmaceutical commercials that promise to alleviate suffering from specific ailments by taking this or that new drug. But wait, you may also experience this barrage of side effects such as blurred vision, diarrhea, nausea, vomiting, feelings of suicide, hair loss, skin lesions, cancer, stroke, internal bleeding, infertility, etc., etc., etc. – are you really willing to take these risks just to alleviate one condition? I suppose it depends on the level of your suffering, but nevertheless, the “solution” doesn’t come without significant trade-offs. And do these “solutions” really address the underlying causes of suffering?

Similarly in regard to invasive species management, have we really done our due diligence to research the potential short term and long term side effects of our current management strategies for eradicating invasive species? For example, do we really know the long-term implications of the widespread use of glyphosate in wetlands? Some studies indicate that glyphosate may pose a threat to human health (including celiac disease and gluten intolerance) and certain species of frogs. What happens when the soils, flora or fauna reach a tipping point in the amount that they can bioaccumulate? Are our “solutions” really addressing the root causes of why invasive species have proliferated? And have we really done due diligence to study these species, learn about them and learn from them – in other words, have we fully considered what hidden benefits these species may be offering in our panic to eradicate them?

blogmarla822142For example, in the American southwest, Tamarix has spread rapidly and has been targeted as an invasive species. Tamarix is a native tree-shrub that was intentionally introduced into the U.S. from Eurasia. Its deep root system, tolerance for saline conditions, and prolific seed production has made it extremely adaptive to riparian areas of the America West where water tables have dropped and water flows and spring floods have decreased. According to a 2008 article in Restoration Ecology, Tamarix is viewed by many as a key factor in the decline of riparian habitats because its establishment occurred concurrently with the decline of those ecosystems. Invasive species in general are seen as a threat to biodiversity. We should be fair, however, and consider a more logical theory that the loss of biodiversity is not the fault of invasive species – they are simply taking advantage of the stage we have set. It’s widely known that invasive species proliferate in areas altered by human activity.

It has been discovered in certain places, that Tamarix actually provides critical habitat for birds, among others, the Yellow-billed Cuckoo whose western population is a candidate for federal endangered species status due to riparian habitat loss. The Southwestern Willow Flycatcher, a federally listed endangered species, breeds in both native (willow) and exotic (Tamarix) habitat types and research by Owen et al. conclude that “there was no indication that birds breeding in Tamarix were suffering negative physiological effects compared to those in native habitats.” (Sogge, Sferra & Paxton, p. 149) This is not to imply that Tamarix is somehow superior or even equal in ecological value to native riparian vegetation. However, the case can be made that it provides an important ecosystem benefit in the absence of suitable habitat for previously existing native vegetation that, for a variety of reasons, may or may not be able to reestablish itself.

Our most recent “solution” to eradicate Tamarix is to introduce the exotic Tamarix beetle. The beetle was imported from Kazakhstan and has an incredible appetite for the Tamarix tree/shrub. However, it is not site specific. This means that it does not discriminate between Tamarix living in areas where it does not offer habitat or ecosystem benefits and Tamarix that is providing critical habitat for threatened or endangered species. What happens when we rapidly eradicate Tamarix without giving sufficient time for willow to reestablish itself? According to Sogge, Sferra and Paxton, Tamarix “can fulfill an important habitat role for some species, especially in areas where degraded riparian systems preclude the establishment of native vegetation.” (Sogge, Sferra & Paxton, p. 150) In fact, they go on to point out that “cuckoos have all but disappeared in the lower Pecos valley from Six-Mile Dam near Carlsbad to the border of Texas following a large-scale Tamarix removal project from 1999 through 2006.”

Invasive species are successional – they take advantage of landscapes that humans have altered and/or degraded and are incredibly adaptive. They survive and flourish where the “native” species cannot. I suggest that in an age of climate change and the recognized need to develop more resilient and adaptive communities and land management practices that we may have a lot to learn from invasive species and a lot to gain by considering them as a component in a more site specific management strategy. Certainly, in many cases they can be too much of a good thing, but in other cases they are providing really important successional and ecosystem benefits. To label them as “invasive” feels unjust and overly subjective. We would be better served by managing them within a more holistic restoration framework for land management that works within a more natural long-term time frame.

And speaking of long-term time frames, we have many species that exist in North America that are widely embraced by society which were originally exotics introduced from abroad such as pheasants, earthworms and honeybees. Pheasants came from western Asia to Europe and then to America. About 33% of U.S. earthworms came over from Europe and 100% of honeybees came over from Europe. Should we stop protecting and restoring pheasant habitat? Should we eradicate all earthworms from our soils? How about honeybees? We have most certainly come to rely on their pollination benefits.

marlablog822144What happens when species move to follow the shift of their habitats due to climate change? If mangroves move into Georgia and South Carolina will we attempt to exterminate them with glyphosate if they displace other species who cannot relocate? And let’s consider Quaking Aspens – a huge tourist attraction out West. Quaking Aspens are the first successional species to repopulate forested areas after a major forest fire. Their relatively short life span allows them “to decompose and put nutrients back into the forest floor more often than other trees.” (Weiber) In fact, according to a recent article, even though they are invasive, they are considered a “keystone species” because they help to maintain local biodiversity. What is displacing them? The conifers and junipers that were there before the aspens.

As expressed in a publication by Dr. Jack Dekker, “The concept of ‘invasive species’ has broader social, economic and political implications, emphasizing the differences in how humans perceive weedy and colonizing species.” (p. 73) He goes on to say “Human perception of what is natural and indigenous, what is disturbed and artificial, is therefore compromised to some degree. In one form or another, willingly or not, the earth is the garden of humanity. The equivocal nature of what harm is caused by invasive species is therefore confounded by the heterogeneous array of human viewpoints and aesthetic values of what is desirable in landscapes. This heterogeneity of opinion is not resolvable but remains at the core of invasion biology because values guide activity and management. For better or worse, the actualization of human values creates opportunity space for new species to invade: they are a direct reflection of human activity.” (p.79)

marlablog822145Indeed, the human species has promoted greater homogeneity year after year – particularly when it comes to agriculture – one of the greatest land modifiers. One of the biggest drivers of homogeneity has been through monoculture farming practices and a market system which favors economies of scale. Driven by profits, we can make more money by reducing per unit costs of production. We all know it costs less per unit to produce a dozen of the same apples than it costs to produce one of many varieties. According to the Food and Agriculture Organization of the United Nations, the world has over 50,000 edible plants. Just three of them, rice, maize and wheat, provide 60 percent of the world’s food energy intake – only a few hundred contribute significantly to food supplies. Just 15 crop plants provide 90 percent of the world’s food energy intake. And let me throw another wrench in this – what about hybrids and genetically modified organisms….

So how does one define “native” species? What are the boundaries (spatial and temporal) for those definitions? Does evolution preclude the concept of preservation? At what point do invasive species become native or do they? I am a fan of preservation and conservation and, as most folks do, I find change to be both exciting and terrifying at the same time. But for Peat’s Sake, rather than adopting eradication as the solution to the presence of an invasive species, let’s sit back, re-evaluate and consider the bigger picture.


A Short History of Honeybees on Earth. Retrieved August 22, 2014 from Let it Bee Apiaries

Blakemore, R.J. (December, 2008). American earthworms (Oligochaeta) from north of the Rio Grande – a species checklist. Retrieved from Annelid Resources, Earthworm.

Buffin, D. and Jewell, T. (July, 2001). Health and environmental impacts of glyphosate: The implications of increased use of glyphosate in association with genetically modified crops. Friends of the Earth.

Dekker, J. (2009). The Evolutionary Ecology of Weeds and Invasive Plants. Retrieved online from Agronomy Department, Iowa State University

Lanctôt, C., Robertson, C., Navarro-Marti̒n, L., Edge, C., Melvin, S.D., Houlahan, J., Trudeau, V.L. (2013). Effects of the glyphosate-based herbicide Roundup WeatherMax® on metamorphosis of wood frogs (Lithobates sylvaticus) in natural wetlands. Aquatic Toxicology, 140-141; 48-57.

Owen, J.C., Sogge, M.K. & Kern, M.D. (2005). Habitat and Sex Differences in Physiological condition of Breeding Southwestern Willow Flycatchers (Empidonax Traillii Extimus). The Auk, 122(4):1261-1270.

Pheasant History, Ecology & Biology. Retrieved August 22, 2014 from Pheasants Forever website.

Reed, G. (April 30, 2013). New Review Points to Glyphosate’s Dangerous Health Effects. Food & Water Watch.

Samsel, A. and Seneff, S. (2013). Glyphosate, pathways to modern diseases II: Celiac sprue and gluten intolerance. Interdisciplinary Toxicology, 6(4): 159-184. SETOX & IEPT, SASc.

Sogge, M.K., Sferra, S.J. & Paxton, E.H. (March, 2008). Tamarix as Habitat for Birds: Implications for Riparian Restoration in the Southwestern United States. Restoration Ecology, 16(1): 146-154.

Staple foods: What do people eat? Retrieved August 22, 2014 online from Food and Agriculture Organization of the United Nations, Agriculture and Consumer Protection Department Corporate Document Repository.

Weiber, A. (August 9, 2014). Aspen disappearing in the West. Retrieved online from Reno Gazette-Journal.

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