Can "Assisted Migration" Save Species from Global Warming?

As the world warms up, some species cannot move to cooler climes in time to survive. Camille Parmesan thinks humans should help even if it means creating invasive species

"As soon as I started to see what an impact climate change was having on wild species and documenting wild species going extinct," Parmesan says, she began to think about how the species might be saved. Short of the world's governments paying heed and cutting greenhouse gas emissions sharply to enable Earth to cool down, she and a few others began pondering alternative actions in particular, human assistance. She sees assisted migration, as the concept has come to be called, as the only hope to save at least some species though certainly only a small minority of those in peril. Jessica J. Hellmann, a conservation biologist at the University of Notre Dame, believes that most assisted migrations will require an advocate who favors a particular species for sentimental or, especially, economic reasons. (Parmesan understandably has several western butterfly species in mind.) Timber companies are already taking climate change into account when planting new trees to be harvested decades hence.

One amateur group, the Torreya Guardians, are attempting to "rewild" the endangered Florida torreya, a conifer tree. Native only to a 65-kilometer length of the Apalachicola River, it began to decline in the 1950s, probably because of fungal pathogens, and is thought to be "left behind" in a habitat hole that has prevented its migration northward. A few dozen seedlings were planted on private land near Waynesville, N.C., last July, with more expected.

Such assisted migration, Parmesan acknowledges, horrifies some conservation biologists: "They spend a good bit of time working against invasive species, and one big cause of species being endangered is being outcompeted by invasive species." In the particular case of the Torreya Guardians, "many biologists are queasy about it because they feel they didn't do the groundwork to see how it would impact the [new] community," she says. So she advocates systematic studies of threatened species' habitats where they thrive and why and what might threaten them.

Better theoretical tools will certainly help. Today's efforts, called climate envelope models, simply consider the temperature, precipitation levels and soil types that a species prefers, then feed that into a standard climate model to predict where a species might naturally migrate, sans human obstacles and assistance. Hellmann is working on a model that incorporates biological elements, such as genetics and competition among species what other species might be attracted or at risk, evolutionary responses, and so on because populations often vary genetically across a species' range. With such data, Hellmann remarks, "we can perhaps get rules of thumb that can help set population priorities."

Assisted migration is a more active idea in academia than among traditional conservation organizations. For example, the Nature Conservancy is studying the idea. "Assisted migration is a relatively drastic option," says Patrick Gonzalez, a climate change expert at the organization, "but might come about if all of our other options fail and a species is in danger of extinction. But it entails a lot of risks."

Such caution frustrates Parmesan, who was a co-author on a 2008 paper in Science proposing a "decision framework" for assessing the possible relocation of endangered species. "If we do nothing, we're also risking biodiversity. Conservation managers have the attitude that doing nothing is good, and my approach is that doing nothing is bad," she explains.

But she is more dismayed by policy makers. In its last months in office, the Bush administration altered the Endangered Species Act to explicitly exclude climate change from factors that would necessitate independent, multiagency studies of species proposed to be protected. Parmesan's reaction was, she says, "mostly unprintable. It's in defiance of what every conservation organization is moving toward." John Kostyak of the National Wildlife Federation says that "chances are very good" for the Obama administration to reverse the regulation, although it could take as long as a year.

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