A couple of months ago, I posted on this site an article that reviewed three garden shows, noting that the third of these, the Ecological Landscaping Association’s Annual Conference, gave its attendees a thought-provoking paradox. One of the event’s speakers discussed the vast and costly damage caused by Japanese knotweed in Great Britain, and another illustrated the nearly hopeless job of managing invasive plants on public lands in Massachusetts.
Ironically, the closing keynote speaker, Ben Falk, touted a brand of gardening – generally termed permaculture – which, in contrast to its many sensible practices, also recommends using plants that can spread far and fast if left untended, disrupting regional ecosystems, i.e. plants that are generally called invasive. The example I used was hardy kiwi: a staple of many permaculture plans, this vine has now thoroughly swallowed up large swaths of once-healthy forest in southern New England and the Midwest. I pointed out the odd contradiction between the movement’s lofty goals and this one clearly harmful practice.
In response to my post, Mr. Falk wrote a lengthy tirade against my “native fundamentalist” misconceptions, in which he extolled the many virtues of modern permaculture, and derided my out-dated “Nativistic War-On-Alien-Invader ideology.”
The ELA posted this lecture in their monthly newsletter, calling it a rebuttal to my piece. Falk’s article did not actually rebut my concerns about the use of invasive plants in permaculture, and instead simply denied the entire concept of invasiveness, but his claims could not be further discussed, since the ELA site allows no comments.
Enter, a few weeks later, Katharine Gehron and Jenna Webster. Both are graduates of the Conway School of Landscape Design (as is Ben Falk), and both are additionally trained in permaculture. Hoping to clarify the issues, Gehron and Webster wrote a thoughtful response to Falk’s article, and asked the ELA to print this too in their newsletter. ELA decided instead to post the article as a pdf in their LinkedIn discussion group where, it must be noted, only group members are likely to see it.
So, to give this informative article the exposure it deserves, here it is again…on an open site that does allow all civil comments. I hope that readers of this blog will also forward this post to friends and colleagues who are involved in permaculture, to get a full range of responses. I myself have also commented on this subject, in a post in this blog entitled “Permaculture’s Internal Contradiction.”
NONNATIVE INVASIVES: A PROBLEM THAT CAN’T BE WISHED AWAY
by Katharine Gehron & Jenna Webster
In “Measuring Progress: Permaculture Responds,” Ben Falk defends permaculture on many fronts without ever directly responding to Sue Reed’s specific critique of a single, yet common, permacultural practice: the use of nonnative species that are or may prove to be invasive. In our estimation, Falk’s response rhetorically sidesteps this important issue, and we feel compelled to write in support of Reed’s argument. While we recognize that permaculture has much to offer society (we have both taken permaculture classes—one of us has obtained certification—and we have both toured permaculture gardens and homesteads, including Whole Systems Research Farm in Moretown, VT, with Falk himself), we could not agree more with Reed on this issue.
Reed writes, “[Permaculturists] promote using several . . . .invasive plants [in addition to hardy kiwi], including autumn olive . . . and oriental bittersweet. . . . What about native plants and insects? What about harm to native ecosystems?”
Falk’s response never acknowledges that such plants have come under scrutiny by many reputable ecologists and environmental advocates for their ability to damage local ecosystem health. Instead, without offering any scientific evidence to back up his position, Falk invalidates this line of criticism by using language such as “Nativistic War-on-Alien-Invader ideology” and suggesting that such an ideology exists solely because some people have a sentimental, irrational bias for North American ecosystems prior to European settlement. He dismissively equates native-plant advocacy with simple nostalgia, stating, “Attempts to maintain . . . an unchanging romantic notion of species assemblage are currently retarding real progress toward enhancing the health of living systems on planet Earth.” This representation severely distorts the position of native-plant advocates. Most of the time, such a generalization is incorrect and a diversion from the discussion.
In his defense of permacultural use of nonnative species, Falk distorts commonly held, scientifically based precepts: “[Permaculture] does not, in general, see plants or other organisms that have been in a place for 10 or 100 or 300 years as fundamentally more ‘natural’ or proper in a place than plants which are recent arrivals.” This is a defensible position only if the person holding it is also prepared to argue that the drastic simplifications in ecological communities which sometimes result from such migrations or introductions are justifiable. We feel that by misrepresenting and ignoring scientific evidence about the workings of ecology and evolution, Falk weakens the credibility of his and his peers’ admirable enterprise to provide food and other human essentials more sustainably.
So, what do scientific studies tell us?
Many native fauna are unable to complete their life cycle with nonnative plants.
Noted entomologist Douglas Tallamy published Bringing Nature Home in 2007 to share with gardeners the results of his studies on the ability of native insects to utilize nonnative plants to support their life cycle. For the fate of biodiversity and the protection of local species, his results are not encouraging. In just one study of insect herbivores found eating woody native and nonnative species, the native vegetation supplied four times more insect biomass simply because the insects’ chewing mouthparts were unable to process alien plants (328). Accordingly, when fewer native insects are available to native birds evolved to eat particular insect species and to feed them to their young, bird populations may also decline (63).
Native fauna have coevolved with native plants over millions of years; accordingly, they are adapted to use native plants throughout their life cycle.
As Tallamy notes in a discussion of humans’ overeagerness to consider a plant “at home” when it is convenient to people, plants have coevolved over millions of years with other species in the places where they live, both influencing and being influenced by the changes in the life forms around them (66). Evolution works at a time scale exponentially slower than the pace of change that humans have caused in just a few generations. Species simply cannot evolve fast enough to adapt to and use many of the plants they have not coevolved with. (We recognize that even within the category of plants we call “native,” there is considerable variation in understanding what that term means, but we will leave these finer distinctions aside for purposes of our argument here.)
Native flora have also coevolved, checking each other’s growth. Nonnatives often have no such checks on the size of their population.
When a plant is introduced to a part of the world where it has never lived before, in many cases the forces that kept the plant in check are suddenly removed, as are the complex and longstanding ecological relationships created by coevolution (Tallamy 66). It’s true that some native species, such as poison ivy and Canada goldenrod, can be aggressively opportunistic and behave like nonnative invasives in certain situations. However, it’s important to remember that many of our native species can use these plants to sustain themselves and their young, unlike the situation with many nonnatives.
The proliferation of nonnative invasives or aggressive native generalist species can be a sign that human activity has disrupted a balance. To the best of our ability, we should mitigate the causes of such disruption. But this obligation does not relieve us of the duty to prevent the introduction of nonnative invasives. As David Jacke points out in Edible Forest Gardens (2005), “Natives may be more likely than nonatives to have unintended benefits, and less likely to have unintended negative consequences.” (vol. 1, 159).
The unchecked spread of nonnatives can be devastating to local ecosystems.
Permaculturists who claim to create complex, thriving, biodiverse landscapes paint an appealing picture, one that is an often beautiful and accurate reflection of their accomplishments, but such language obscures the great harm that can result when certain practitioners plant and advocate for the planting of species with the ability to spread far beyond one person’s garden or farm. Such plants can overwhelm local plant communities, often on a massive scale, replacing diverse assemblages of coevolved species with biologically unstable near monocultures. The consequences of these conversions—besides the increased use of herbicides and the need for ever-greater management efforts from already overtaxed farmers, municipalities, conservation agencies, and other land stewards—include, among other things, the alteration of hydrological cycles and water quality, changes in wildfire frequencies and intensities, and the degradation of aquatic habitats as a result of soil erosion (Tallamy, 85).
Even if a nonnative plant does not demonstrate invasive tendencies now, that does not mean it will not do so in the future.
Falk observes, as have other permaculturists, that humans have been moving plants and animals for thousands of years. This is certainly true, but it does not equate that past anthropogenic plant dispersal, intentional or not, absolves us from exercising extreme caution when introducing plants for human benefit. This is especially true when we consider present-day ecosystems, which are experiencing profound stresses, from climate change to acid rain to habitat fragmentation, on orders of magnitude unknown thousands of years ago. Such stresses have made many of today’s landscapes more susceptible to domination by plant species removed from their original contexts, and from the ecological constraints imposed by those contexts. In fact, as ecologist Steven Apfelbaum noted in his book Nature’s Second Chance: Restoring the Ecology of Stone Prairie Farm (2009), nonnative plants that do not currently appear to have invasive tendencies may well prove invasive in the future due to human-induced changes in soils, climate, hydrology, and/or other conditions (180-81).
Finally, on related note, we would like to address what we feel to be an inappropriate parallel Falk draws between the spread of humans and the diversity of human cultures, and the spread of plant species. He writes, “ In [Sue Reed’s] vision of a ‘native’ world, would she like to see all but the first (indigenous) peoples removed from the ecosystem in which they have artificially been introduced – including us Europeans in North America?” Surely, we would all agree that our success in building a more respectful, diverse, multicultural society is to be much lauded. However, Falk’s article would seem to suggest that permaculture is helping to make the world more ecologically “cosmopolitan” faster, and that this is as good and right as our multicultural global society. Yet human multiculturalism is not analogous to the introduction of alien plant species. Arguments linking the structure of human society with the mechanisms of the natural world have been made before, and in ways that have proved deeply problematic. We feel that such comparisons should be done with the greatest of caution, as they often serve to further ideological goals and are frequently without basis in scientific evidence.
While we wish to thank Falk and other devoted permaculture practitioners for taking on the difficult work of helping build the foundation for localized, non-corporate, environmentally sustainable systems designed to provide food, energy, medicine, materials, and other essentials, we believe—like Sue Reed—that the evidence about the negative effects of invasive species is too important to ignore.
Katharine Gehron holds a master’s degree from the Conway School, a graduate program in sustainable landscape planning and design. Her professional experience includes land-use consulting, green cemetery advocacy, and sustainable residential landscape design. She will be attending the Yale School of Forestry and Environmental Studies in the fall to pursue a master’s degree in environmental science.
Jenna Webster is a designer with Larry Weaner Landscape Associates (LWLA). At LWLA she has been involved with master plans for small and large residential and public projects, in addition to helping plan and implement educational programs for LWLA’s affiliate, New Directions in the American Landscape. Prior to joining LWLA she received a master’s degree from the Conway School, a graduate program in sustainable landscape planning and design, and worked for Natural Landscapes Nursery (a wholesale native plant nursery) as well as land preservation agencies in southeast Pennsylvania.
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