Saturday, September 26, 2009

Invasive species issues & the danger of being controlled by dogmatic ecological paradigms

Invasive species issues are wickedly inconvenient. Martha Proctor, a UC Master Gardener, writes that “[n]on-native invasive species crowd out native species by abundant seed production, rapid growth, efficient use of resources and better access to moisture during the dry summers. Invasives outcompete natives, displacing the native habitats of fish, insects, birds, plants, butterflies and other wildlife.” (Copyright © 2008 - Marin Independent Journal Posted: 09/25/2009) The rapid introduction into an ecosystem and establishment of invasive species therein create a raging uncontrollable biological wildfire.

The impacts of invasive species on an ecosystem are measured by the changes in ecological interactions. Thinking of ecological interactions in terms of competition, predation, parasitism, mutualism, commensalism and symbiosis helps to demonstrate the possible negative impacts of non native or exotic species of ecosystem services. Competition – two species share a requirement for a limited resource reduces fitness of one or both species; predation – one species feeds on another enhancing the fitness of a predator but reducing the fitness of prey; parasitism – one species feeds on another enhancing fitness of parasite but reducing fitness of host; mutualism – two species provide resources or services to each other enhancing fitness of both species; commensalism – one species receives a benefit from another species enhancing fitness of one species with no effect on the fitness of the other species; symbiosis – two species live together can include parasitism, mutualism, and commensalism.[1] The disruption of any of these creates cascade of change in the effects of multiple interactions throughout the system. If the effects are large enough, the original system is stressed and its traditional expected resource services reduced and perhaps even eliminated. So, if one wants to play baseball with a traditional wooden bat, native ash trees are selected and shaped for the native sport. The introduction and reproduction of the emerald ash borer dynamically limits access to the resource by killing the ash trees that are needed to make baseball bats.

However, the wicked inconvenience of invasive species is not the introduction of exotic aliens to ecosystems, but rather the danger of being controlled by dogmatic ecological paradigms based upon dichotomous assumptions superimposed upon the systems of nature that do not have goals and expectations per se. Writing in his new book, a courtesy copy of which was send to me without charge, “Invasion Biology”, Mark Davis notes the tendency of ecological professionals to categorize invasive species issues in a series of yes or no, in or out, with us or against us matrices or frameworks for discussion. The result is that we think in terms of “…two types of species: native vs non native, native vs exotic, indigenous vs non-indigenous, invasive vs non invasive.”[2] The human artifice of a dualistic interpretation leads us down the path of unexpected and unintended consequences or as I now call it on Twitter (@InvasiveNotes) – Collision of Desires. We are propelled towards a management course that suspects the intentions of novel ecosystems even though that means placing a human qualitative measurement upon the system. Thus we are predisposed at a high policy making level to think that every introduced species is intrinsically bad or evil. But the status of being non native is a “…position in evolutionary history [that] does not quality as an ecological category with distinct and consistent properties.”[3] And further, we are compelled unwittingly to consider every altered system to be dysfunctional and in need of mitigation in order to return it to a past state.

Ecosystems are not static and when new species are introduced a new, novel system is created. Some of the interactions, relationships or functions of the novel system will provide desired resources as well as numerous negative impacts. For example, tamarisk, has become a poster child for a new species introduction whose removal may now negatively impact a desired species, southwestern willow flycatcher. (Agriculture Department Forced to Re-examine Tamarisk Leaf-eating Beetle Program That Hurts Endangered Songbird) It is important to bear in mind that the introduction of tamarisk was for its ability to provide ecosystem resources and services such as “…ornamental values (e.g., T. chinensis and T. ramosissima), others for planting in wind breaks (e.g., T. aphylla) or to stabilize eroding stream banks. (Neill, 1985)” [4]

Conservation and preservation are tinged by dualistic thinking with a patina of nationalistic nostalgia for, what I call, a desire to return to a “Leave it to Beaver” time and place, a Golden Age of and for a select few. The nostalgia on the part of a few stakeholders causes among other things the reaction and rise of the environmental justice movement. The wicked inconvenience arises because there is no easily accessed set of right or wrong choices when it comes to invasive species. The German Shakespeare, JW von Goethe, said that there is “… no past that we can bring back by longing for it. There is only an eternally new now that builds and creates itself.” On the other hand, doing nothing, either from paralysis of analysis or waiting until there is nothing to be done is an invitation to extinction. If the world’s farmers took a position of hopelessness in the face of nature we would all starve.

With invasive species issues, looking for final, absolute solutions results in a chronic series of hapless unintended consequences. The choices should be based on adaptation to change with the knowledge that we need and are partners with our ecosystems; and as a gardeners in the landscapes we must work daily to ameliorate impacts while allowing resources to be used and encourage systems that are self sustaining with minimal hyper-extra-eco-system input from humanity.

[1] (
[2] Mark A. Davis. Invasion Biology. Oxford University Press. 2009. p.163 (
[3] Mark A. Davis. Invasion Biology. Oxford University Press. 2009. p.164 (
[4] Roland C. de Gouvenain. Origin, History and Current Range
of Saltcedar in the U.S. Saltcedar Management Workshop, June 12, 1996.


Leslie said...

I read your blog and this entry with much interest. This is really a fascinating and difficult subject.
Two comments: I garden professionally in Marin County and read the IJ article you linked to. The newspaper erroneously noted that Pampas grass and French broom are still cultivated in the horticultural industry. The Pampas grass sold on the market is sterile. French broom is not allowed to be sold, but other non-invasive broom are sold. Many people confuse these as, esp. the Grass, is a look-alike.
My other thought: I have often wondered, especially in the West, how much our suppression of fire, a natural phenomenon in the west's ecology, has helped along these invasives. For instance, one of the worst 'invasive' is our Sudden Oak Death, caused by a fungal pathogen. Oaks are naturally resistant to fire, especially low grade fires. Native American used fire for many reasons, and especially to help the acorn crop. They also 'weeded' around the oaks. Without our natural fires, I feel that fungal pathogens are allowed to build up in the soils. In addition, our native bunchgrasses are resistant to fires, whereas the annual grasses that cloth the hillsides of California now are not.
I understand the idea you present of our dichotomous assumptions and I agree. But we need to take all this to a much deeper level, for we are trying to control i.e. manage ecosystems based on our extremely limited knowledge. This applies to wildlife as well as plants as you note. In Australia, the biologists have finally realized that their aborigine companions knew how to manage the land and did for 50,000 years whereas the whites mucked it up royally in just 200 years. They now are forming partnerships between aborigines and biologists in land management.
Very complicated issue. Love your writing and the blog. Thanks.

Cindy said...

Interested to see your reference to the dualistic nature of Western Culture, yes, no, black white..when all is continuum, in flux.

Your original contribution is to clarify for us, that we must accept dynamic equilibrium in natural systems, but that once we have overstressed such systems, we cannot just throw up our hands, but must try to reestablish equilibrium at a different point.

Anonymous said...

"However, the wicked inconvenience of invasive species is not the introduction of exotic aliens to ecosystems, but rather the danger of being controlled by dogmatic ecological paradigms based upon dichotomous assumptions superimposed upon the systems of nature that does not have goals and expectations".

This is a great sentence. I'm not wholly sure I agree with your philosohpy, but it is a great sentence nonetheless.