The futility of eradicating non-native species

We tend to focus on the native plant “restorations” in our neighborhood, but we should not lose track of the fact that similar efforts are taking place all over the world.  The native plant movement is international and if it loses momentum, we should expect to see loss of support for its destructive projects elsewhere.  So, today we will tell our readers about several recent developments that suggest that scientists all over the world are having second thoughts about invasion biology, which is the scientific underpinning of the native plant movement. 

Second Thoughts:  The Hawaiian Case

We have reported to our readers about the many “restoration” projects in Hawaii.  There is some logic to focusing such efforts on islands, because they are the places most vulnerable to the loss of native species attributed to introduced species and theoretically they are also the places where re-invasion should be easiest to control.

Scientists have recently published the results of a ten-year effort to return an “invaded” forest to its native origins.  They spent about 5 years clearing the forest of all non-natives.  They planted the scorched earth with natives and then they walked away from it to observe the long-term sustainability of their effort.  Five years later they report that the composition of the forest—with respect to its nativity—has essentially returned to its original state.

They tested several hypotheses while observing the changes in the forest during the second half of the project.  Conventional wisdom had been that the more densely natives occupied the ground, the less vulnerable it would be to re-invasion.  Much to their surprise, this was not the outcome of their experiment.  The more densely natives occupied the ground, the greater the population of non-natives in the final analysis.  They conclude that the same conditions which encouraged the growth of native plants were equally beneficial to the growth of non-native plants.

This study was conducted by the US Forest Service.  We hope they learned something from this experience.  Specifically, we hope that the US Forest Service now understands that native plant “restorations” are not a one-shot deal.  They are a permanent commitment to garden that restoration with the same amount of effort.  That’s why scientists—such as Professors Arthur Shapiro and Peter Del Tredici—tell us that large scale projects are not sustainable in the long term.  A small scale native plant garden as an historical illustration is a worthwhile effort.  Gardening our vast public lands is like “plowing the sea,” as Professor Shapiro told us recently.

Second Thoughts:  The New Zealand Case

New Zealand has made herculean efforts to save its native species from “invasions” by non-native species:  “New Zealand is a very weedy country.  Indigenous plant species are matched in number by naturalized exotic species and about 20 new invaders are discovered each year.  Thus, a weed eradication program has been under way for the past 10 years, but eradicating an unwanted plant species is much more difficult than it might seem.” (1)

Eradicating yellow tree lupin, New Zealand Dept of Conservation

How successful have these efforts been?  According to a recent study, they have had very little success:  “The current issue of the journal Invasive Plant Science and Management assesses the progress of 111 weed eradication programs carried out by New Zealand’s Department of Conservation.  Only four of these programs have met with success, while 21 have been discontinued and the rest remain an ongoing challenge.”

The report concludes, “After a decade, New Zealand’s weed eradication strategy has yet to yield significant results.”  Anyone who has been watching similar efforts all over the San Francisco Bay Area will not be the least bit surprised by this conclusion.  With the exception of small gardens which are irrigated and intensively gardened, these projects are weedy messes, usually behind fences.

Second Thoughts:  The Australian Case

Scotia Sanctuary, Australia

Emma Marris interviewed the manager of one of many “restoration” projects in Australia for her book, Rambunctious Garden.  He told her about the 18 month process of killing all non-native animals in a 15-square mile sanctuary enclosed by a prison-like fence, “sturdy, tall, and electrified.”  (This was half of the Scotia Sanctuary)

“He was able to shoot out the goats in a matter of days.  Rabbits were harder…he put out carrot bait…the rabbits…would learn to trust the new food source…[then] the carrots would be poisoned…[He] repeated this routine three times, running through 12,500 pounds of carrots…For each fox, he learned its habits and was eventually able to find perfect places to trap or poison them.  He also trapped cats…The key to making it work, he says, was ‘perseverance, perseverance, perseverance.’” (2)

It was necessary to kill all the non-native animals before taking on the more difficult task of returning the land to native plants because of the interaction between the plants and animals.  The non-native animals are considered a continuing and permanent threat to the sanctuary.  The expectation is that this 250 acre restoration will require human intervention indefinitely into the future.

Australia is a huge place, so the prospect of this labor-intensive process being replicated on a nationwide basis is absurd.  Therefore, it seems inevitable that Australian scientists would begin to question the efficacy of such efforts. 

Just two months ago, an Australian scientist, Angela Moles, gave a TED (Technology, Entertainment, and Design) presentation suggesting that it is time to grant Australian citizenship to introduced species.  Click here to see the video.

Her reasoning is based on the relatively new understanding of the speed with which evolution occurs.  Her laboratory used the collection of a university herbarium to measure the changes in the plants that were introduced to Australia.  The herbarium had samples of the same species of plants collected over a 60 year period from the same location.  They found that the plants had changed in significant ways.  In a sense, they were becoming Australian plants in response to the biotic (other plants and animals) and abiotic (climate, soil, etc) conditions of their new home.  She predicted that if they weren’t yet genetically distinct from their ancestors, they soon would be.   In other words, they are becoming distinct, new species…..Australian species.

She showed a slide of her son who is a 2nd generation Australian.  He is considered an Australian by law and custom.  Then she showed a slide of clover which has changed significantly since its introduction.  After 130 generations, it is still not considered Australian.  After showing a few of the massive eradication projects and describing the scale and futility of those efforts, she suggested that it is long past time to accept the clover and other introduced species as Australian.

And, of course, we agree.  Let us abandon the destructive and futile war on non-native species.  The sooner we do, the less damage will be done to the environment and to the animals that live in it, including us.  


(1)    “Eradicating Weed Species in New Zealand Poses a Larger Challenge Than Expected,” Science Daily, July 21, 2012

(2)    Emma Marris, Rambunctious Garden, Bloomsbury, 2011

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