Are critics of invasion biology pessimists or realists?

The California Department of Food and Agriculture held a symposium about invasive pest management in the 21st Century on October 17, 2013, at UC Davis.  This second in a series was focused on insects and diseases.  The first symposium held in Oakland in June 2013, focused on “invasive” plants.

The keynote speaker at the second symposium was Professor Daniel Simberloff of University of Tennessee.  He is a prominent invasion biologist and a self-appointed defender of that scientific discipline.  When the assumptions of invasion biology are questioned by other scientists, Professor Simberloff often publishes a heated response and recruits others to join him.  (For an example, see our recent post about Ascension Island and visit his “Counterpoint” to the article on which our post was based.)

Given the many recent defections of scientists from the central assumptions of invasion biology, we anticipated that Professor Simberloff would acknowledge that invasion biology is under siege.  We were not disappointed.  He started his talk by showing a quote from a scientist on the Galapagos Islands who, after decades of trying to eradicate non-native blackberry, was admitting defeat.  To paraphrase the scientist, he no longer believes that eradication is possible.  Therefore, he is now willing to call it a native plant.

These blackberries were mowed to the ground sometime in the past year.  Herbicides haven't been used in the Sutro forest for several years, but UCSF plans to use them in the future.  Courtesy Save Sutro
These blackberries in the Sutro forest were mowed to the ground sometime in the past year. Herbicides haven’t been used in the Sutro forest for several years, but UCSF plans to use them in the future. Courtesy Save Sutro

We were reminded of Professor Matt Chew’s criterion for what species “belong” in any particular location.  If the species persists unassisted in that location, Professor Chew believes it belongs there.  Surely a corollary to that criterion should be, “if you can’t eradicate it, it belongs there.”

Professor Simberloff diagnoses this acceptance of non-native species as pessimism.  He is not alone in this characterization of people who are no longer willing to spend unlimited amounts of time and money trying to kill non-native species.  This is the standard criticism of that viewpoint.  We are called defeatists who have “given up” in the internet debates we read.

Why are we critics of invasion biology?

Although we agree that it is usually futile to try to eradicate non-native plants with large, well-established populations that have long ago naturalized in our environment, this is not the primary reason why we reject the notion that there is some benefit to trying anyway.  The main reason why we reject the fruitless crusade against non-native plants is because of the damage it does:  the herbicides that are sprayed on our public lands; the release of tons of carbon dioxide into the atmosphere when trees are destroyed; the loss of habitat for wildlife, etc.

At the same time, we acknowledge that some invasions of insects and diseases have posed such serious economic and health threats that we have no choice but to make every effort to eradicate them.  The species of mosquitoes that carry yellow fever and malaria are examples of justified eradication efforts.  We hope that those who are engaged in that effort are also mindful that the methods used are not more harmful than the targets.

Scientists defend “novel” ecosystems

We harp on these issues because they are not discussed by the scientists who either defend or critique invasion biology.  Their concerns are, so to speak, academic.

Sutro Forest is a novel ecosystem. Courtesy Save Sutro

There is an excellent description of the scientific debate about “invasive species” in the on-line newsletter of the American Society of Landscape Architecture (ASLA).  They report that novel ecosystems were featured at the recent conference of the Society for Ecological Restoration (SER) held in Madison, Wisconsin.  Novel ecosystems were defined by one of the speakers (Eric Higgs, University of Victoria) as ecosystems in which changes from historical conditions are considered irreversible: “Even if plants are removed, ‘the system will revert back immediately’ to a state of invasion.”  This is an accurate description of 15 years of effort by San Francisco’s so-called Natural Areas Program.  Non-native plants are repeatedly yanked out and/or poisoned, native plants are planted, native plants die, non-native plants return.  That cycle is repeated annually in some high-priority locations.

Apparently, we are not alone in observing this futile cycle.  The ASLA description of the conference of the Society of Ecological Restoration summarizes current thinking of practitioners of that profession:

“In the face of this overwhelming struggle against novelty, there has been a shift in values among society. Years ago, restoration ecologists wanted to restore ecosystems to their “historic fidelity” as much as possible. Now, ecologists, scientists, and landscape architects discuss the value of novel ecosystems’ services, which to some extent are plant-agnostic.”

While this viewpoint is a welcome improvement over the previous fantasies of restorationists, this information has not yet reached managers of public lands in the San Francisco Bay Area.  Nor does it acknowledge the very real damage that is being done by those who cling to the fantasy that non-native plants can be eradicated and replaced with native species, particularly in an urban setting such as the Bay Area.

The mission of Million Trees is not an academic exercise.  Our objective is to stop the damage being inflicted on our environment and the animals that live in it.  And we don’t intend to shut up until the damage has stopped.  We hope to be put out of business within our lifetime.