Mussels and Ferns and Worms, Oh My!

Complexity in the Field
By J.B. Ruhl
Post 2
August 18, 2006

Among the “wicked” problems confronted in environmental law and policy, none illustrates complex system behavior better, and with such alarming results, as the invasive species phenomenon. Of course, what’s invasive to an ecosystem versus merely part of its natural evolution of species assembly is to some extent a normative judgment humans make. Resilient ecosystems adapt to disturbance regimes such as flood and fire, which are engines of species introduction, so as to strengthen resistance to perturbations. And some “invasions” yield desirable results for humans—Hawaii wouldn’t have much to offer if it hadn’t been invaded by wayward birds at some point.

Usually what we are talking about when referring to invasive species are anthropogenically-induced introductions of species that wildly tilt the species assembly. As such, they are examples of how seemingly small perturbations can lead to disproportionately large system effects, even going so far as to cross the threshold and shift the system into an entirely different set of rules. They also illustrate how excruciatingly difficult it can be to try to set back the clock of a complex adaptive system. Eradicating an invasive species once the system has shifted into a new state has proven to be no mean feat for restoration ecology.

Almost everyone has heard of the zebra mussel, the poster child of invasive species. It’s here to stay, the only question being how much larger beyond the Great Lakes region “here” becomes. Legal controls on the initial source of the highly efficient little bivalves—ship ballast discharges—won't send them home, though they might help limit future such occurrences. Some sources of invasion can’t be controlled by any means, legal or otherwise, such as the winds that likely blew spores of the Old World climbing fern across oceans and into the cypress forests of the Florida Everglades, where it has cloaked tens of thousands of acres in literal death.

In some cases the causes of invasion seem benign, and people can hardly believe the invasion is real. I’m talking about none other than worms. Earthworms, ubiquitous in many parts of the country, are not native to the northern United States and Canada—the glaciers scoured them away ages ago. An integral part of these northern forest ecosystems is the layer of “duff” on the forest floor, upon which many species depend for shelter and food. Anglers and other human travelers have “innocently” introduced earthworms throughout the region, and, not surprisingly, earthworms are voracious consumers of duff. Within five years after worms arrive on the scene, the duff is gone and the worms move on. The worm populations spread outward at a rate of about 20 feet per year, leaving behind a denuded forest floor of little value to native species and, because of higher nutrient levels worms leave behind, highly vulnerable to invasive plant species. The problem is so serious that Jim Chen's home base University of Minnesota has devoted a website to it called Minnesota Worm Watch.

The message from this for law is not especially promising. Quarantines, checkpoints, and penalties designed to catch or deter human introductions of species need to be comprehensive, overbroad, and draconian if they are to prevent that one little slip-up, which they are unlikely to do anyway, and they are of little use once the slip-up occurs. At the other end of the spectrum, there is evidence that global climate change, because of its ubiquitous effects on ecosystem resistance, has amplified the success rate and persistence of invasive species once introduced, but there's a topic that has presented its own set of wicked challenges for law and policy. As an example of the “law and complex systems” breed of legal challenges, therefore, this one may be more than law can handle. We may be better off thinking of the law of invasive species more in the category of disaster preparedness and response that Dan Farber’s series is covering.