Deciding when to move plants and animals to save them from global warming

Eric Baetscher Checkerspot Butterfly

Climate change threatens hundreds of thousands of species, including the colorful San Francisco Bay checkerspot butterfly, with extinction. Now Stanford University scientists, along with a multidisciplinary research team, are proposing when and how to save the Bay checkerspot and other vulnerable species by moving them to suitable new habitats.

As the climate warms and alters the global ecosystem, many plants and animals will find themselves in habitats too warm or physically altered. For some, it may be a case of move or die. Some researchers have proposed using "managed relocation," or assisted migration, to help move vulnerable flora and fauna to habitats where they are more likely to thrive.

A team of scientists, including two from Stanford's Woods Institute for the Environment, has developed a model for deciding if, when and how species can be viably relocated. Their work will be published this month in the online edition of the Proceedings of the National Academy of Sciences.

"We've got to move things," said Terry Root, co-author of the PNAS paper and a senior fellow at the Woods Institute. "We could have about 400,000 species going extinct if the temperature increases by two degrees Celsius, and I don't really see how it won't, given our actions this far."

Moving that many species is not feasible, Root said. And while some species are physically relocating themselves, many cannot, including trees and animals in isolated environments, she added.

The creatures that live on the Sky Islands, a mesa in the Arizona desert, can now live there nicely, Root said. "But as soon as it starts getting warmer, they are going to cook," she said. "And they can't scale themselves down the mesa, across the desert, and find somewhere else to live. They need our help."

New model

The PNAS paper proposes a new management tool for choosing which species are most viable for relocation based on a series of social and ecological criteria—for example, how much is known about the biology, geographical distribution and the ecological uniqueness of the species, as well as how easy they are to catch and move. Social factors, such as cultural importance, financial impact and even the laws and regulations regarding the species, also are considered.

"You have to know a lot about their biology and their habitat needs before you can move them," Root said. "Otherwise they're not going to make it."

In the PNAS study, researchers looked at three examples—the Bay checkerspot butterfly and two types of trees—where managed relocation might be a potential intervention strategy as the climate warms. They ranked the species in terms of movement feasibility and also looked at managed relocation from the perspective of two hypothetical stakeholder groups: proponents and opponents of the tactic. Based on what's important to each group, managed relocation might be more or less viable.

"Basically, any organism that is deemed 'important' for whatever reason could be a candidate for managed relocation," said lead author David Richardson of Stellenbosch University in South Africa.

For example, Bay checkerspot butterflies are seriously threatened by climate change and habitat destruction. But while moving vulnerable butterfly populations farther north might seem like a terrific option to conservationists in the greater San Francisco Bay Area, those living in northern California and Oregon may not want the insect introduced for fear that it will compete with local butterflies.

Other risks

This new model also addresses other concerns with managed relocation, including the risk of inadvertently introducing non-native species to a new environment. Many non-natives and invasive species cause devastating and irreversible damage to their new ecosystem. But the model considers these risks, allowing managers to make informed decisions.

"I really hope that our framework will encourage a more open discussion on the topic," Richardson said. "Make no mistake, managed relocation is, and will always be, a risky business, but once a framework is in place whereby all parties can express their views, and levels of uncertainty are clearly expressed, we have a chance of being able to make progress."

The most exciting thing about the PNAS paper, Root said, is that it brings to light that global warming is hurting nature. "I think people are finally realizing we're losing species," she said.

Root compares taking action on climate change to paying your taxes. "When we individually pay our taxes, it's just a pittance and forms a tiny piece of the whole United States budget," she said. "But when everybody pays, it's huge. Everybody can do something to help."

Stephen Schneider, a professor of biology at Stanford and senior fellow at the Woods Institute, co-authored the PNAS study. The manuscript was edited by Paul Ehrlich, a professor of biology at Stanford. Support for the study was provided by the National Science Foundation.


Cassandra Brooks is a science-writing intern at the Woods Institute for the Environment at Stanford.