Beyond Kudzu: Can Non-Native Species Benefit an Ecosystem?

If you’ve worked on a project that calls for revegetation using native seeds, or if you’ve ever dealt with an area that’s overrun with an invasive species like the tenacious kudzu vine—considered a noxious weed in the US—you likely have an opinion about the introduction of non-native species to an ecosystem. The list of flora and fauna run amok is a long one. This article from the Wall Street Journal, “Invasion of the Alien Species,” lists some of the more notorious non-native species that have caused problems across the globe: “In the Mississippi River, it is Asian carp; in the Everglades, Burmese pythons; in the Great Lakes, Russian zebra mussels; in the South, Indochinese kudzu vine. In Australia, cane toads from South America; in Lake Victoria in Africa, water hyacinth from the Amazon; in Germany, Chinese mitten crabs; in the Caribbean, lionfish from the Pacific. A fungus spread by African clawed toads (used in laboratories) has wiped out frogs in Central America.” And the list continues of native plants and animals that have been virtually wiped out by thriving non-native species that either kill them outright or simply outcompete them for scarce resources.

Non-native species often thrive because they have no natural predators in their adopted environment. One solution, the article notes, is to bring in predator species from the invader’s native environment, or from some other environment, to control them. Also known as biological control, it seems like an obvious solution, but much can go wrong, as we’ve occasionally covered in Erosion Control. For example, the US Department of Agriculture released salt cedar beetles from Kazakhstan in Colorado to control the invasive tamarisk, or salt cedar, shrubs that had once been imported to plant as windbreaks and control erosion, but which eventually crowded out native plants like cottonwood trees. The salt cedar beetles began killing not only the tamarisk but also other plants critical for the survival of endangered birds.

The WSJ article suggests, though, that non-native species aren’t always a bad thing, that they can increase biodiversity in their new home and create additional benefits. Zebra mussels, it points out, have effectively filtered the water of Lake Erie and made it clearer, and in the Southwest the tamarisks—which are still there, despite the efforts of the salt cedar beetles—have become preferred nesting sites for the willow flycatcher, one of the region’s endangered birds.

While globalization and increased movement of people and goods around the world have made it easier for non-native species to reach new habitats, scientific advances are allowing us to reverse the process in many cases. Vaccines that cause sterility—and which can sometimes be administered in food—can sterilize members of an invasive species; there is hope in Great Britain that this technique might eliminate the gray squirrel, which has crowded out native rodents. Genetic manipulation of the Aedes mosquito is being used to battle the Zika virus in parts of Brazil; modified male mosquitoes released into the environment father larvae that will not reach maturity, thereby reducing the overall mosquito population.

Have you worked on a project that’s using biological controls to curb a non-native plant or animal species? Under what circumstances do you think introducing one species to control another is warranted? How about the use of widespread vaccination or genomics?

Continuing Education

Here are some upcoming webinars—two of them free!—from Forester University that will be of interest to erosion control professionals.

Designing for High-Flow with Concrete-Enhanced Synthetic Turf—Free Webinar

September 27

Speaker Bradford Cooley, P.E., discusses applications of concrete-enhanced synthetic turf (CEST) revetment systems, design and installation best practices, hydraulic and non-hydraulic performance results, and how you can implement CEST at your site to improve performance and reduce maintenance costs. Sponsored by Watershed Geo.

Click here for more information and to register.

Specifying Engineered Soils for Sustainable Vegetation—Free Webinar

October 26

Returning speaker Marc S. Theisen, CPESC, CPSWQ, CESSWI, discusses how to specify Engineered Soil Media (ESM) as a cost-effective alternative to topsoil, compost, and other conventional organic soil amendments. Topics include testing your soil for organic content, selecting proper ESM application rates, calculating the cost benefits, and applying the best practices from real-world case studies and research. Sponsored by Profile Products LLC.

Click here for more information and to register.

Fire and Rain: Post-Fire Erosion Control Master Class Series

October 6 – November 3

This five-part master class series covers post-fire erosion control applications, techniques, and best practices, including post-fire hazard assessment, secondary disaster impacts, watershed hydraulic changes, remediation access and funding, post-fire BMP selection and implementation, accountability issues, and emergency measure implementation. The five live and on-demand lectures are followed by open Q&A sessions. Speakers include Mike Harding, Julie Etra, Ian Paton, Andrew Earles, and Kathleen Harr.

Click here for more information and to register. EC_bug_web

  • Hi Janice, I would like to clarify a few incorrect statements regarding tamarisk and the tamarisk beetle.
    The endangered birds you mention (the Southwestern Willow Flycatcher and the threatened Yellow-Billed Cuckoo) nest in native willow trees. Since tamarisk has a similar branching and leaf structure as willows, these birds have adapted to also nest in tamarisk.

    Tamarisk beetles have impacted endangered bird habitat not because the beetles eat other plants that the birds nest in, but because the beetle defoliates the leaves of tamarisk trees that the birds are now nesting in. When tamarisk leaves are defoliated by the tamarisk beetle, the nests of the birds are then exposed to predation and higher temperatures due to loss of shade.

    So to clarify: the tamarisk beetle only eats tamarisk, as it was originally intended. Tamarisk is not the preferred nesting site for these endangered birds, but due to loss of native habitat (e.g. willows) from tamarisk infestation, the birds have little choice.

  • Matt Chew.

    So far, like the previous commenter, I have not seen any reports that Tamarisk leaf beetles are eating anything besides tamarisk leaves. That doesn’t mean they never will; insects are notoriously quick to evolve new adaptations. Whether the birds in question actually “prefer” willows is an open question and perhaps not a very salient one; the fact is that they do nest in tamarisks, so the plants are not a threat to the birds as claimed in the original FWS listing notices. Finally, it should be noted that, while the USDA initiated beetle releases, in 2010 the agency canceled and repudiated the program because defoliating tamarisks during the nesting season increased the threat to the listed birds, and also because the program did not meet its own original criterion of releasing only beetles that would not spread to areas where the birds relied on tamarisks. Instead of one very specific type with strict latitudinal habitat requirements, up to five different types with a wide range of tolerances were released. Since then, beetle releases have been conducted legally only by states, within their own boundaries, as interstate transport of the beetles is prohibited. Colorado has been the most enthusiastic continuing producer/releaser of tamarisk leaf beetles. Unsurprisingly, they have not trained their beetles to recognize state lines; furthermore evidence suggests that private individuals are also illegally moving beetles. However well intentioned the programs were at the beginning, now they’re a mess. Politics and personal ambitions are making it a bigger mess.

  • Matt Chew.

    Tamarisks aside, what “benefits an ecosystem” isn’t really self evident. Different people want different things from ecosystems, but what anyone in particular considers personally beneficial for any reason tells us nothing about the ‘good of the ecosystem’. Most people don’y like unexpected or unintended change. Ecosystems dynamic, unbounded concepts. They may not even be objects, much less individuals. That makes it pretty hard to argue that anything besides ongoing change is ‘good’ for an ecosystem. Valuing the persistence of a particular configuration under changing conditions that generate new ecological configurations seems ill-conceived.


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