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Global warming will cause flora and fauna to migrate

Dec 29, 2009

Animals and plants will have to migrate to keep up with shifting climate belts caused by global warming, says a new study. Those in mountain regions, however, face a lower risk of being overtaken by changing climate due to large temperature swings with altitude.

One upon a time, adaptation to global warming was dubbed a cop-out, a way to duck the challenge of reducing, and ultimately eliminating, greenhouse-gas emissions from cars, factories, and power plants.

Now, however, the issue is front and center – a necessary adjunct to reducing emissions. One significant adaptation challenge involves protecting as much of Earth's biodiversity as possible in what is projected to be a prolonged period of rapid – if sometimes erratic – warming.

Enter Scott Loarie. a researcher at the Carnegie Institution's department of global ecology in Stanford, Calif. He and five colleagues have unveiled a new approach to assessing how changing climate will affect various habitats. They dub the measure "climate velocity."

The measure takes into account changing temperatures as broad climate zones migrate north and south away from the equator, and hike their way up the sides of mountains. And it looks at the geographic setting in which the habitats appear – whether on a broad flat landscape or in mountains, for instance.

One broad observation from the data: plants and animals that live in broad, relatively flat areas – the Great Plains, regions containing mangrove forests, or the African Veldt – are likely to have the toughest time dealing with global warming.

Organisms living there must migrate or have their seeds dispersed over long distances to keep up with climate belts that are moving more rapidly than many species can match. This is especially true for plants and animals that live in patchy, geographically small protected areas. Habitats are fragmented, often with no "corridors" connecting them to allow for easy migration.

Plants and animals in mountain regions, on the other hand, appear to face a lower risk of being overtaken by global warming, because mountains exhibit large temperature swings with altitude; it's a fairly short walk or flight up-slope to reach a more hospitable climate zone. The exception: organisms that live on mountain summits and have nowhere else to go.

The work Dr. Loarie and his colleagues have done is adding a new tool to conservationists' quiver, says the University of Maryland's David Inouye, who heads the graduate program in sustainable development and conservation biology there.

"It gives an idea of how quickly changes are going to be happening and where they are going to be happening most rapidly," he says during a phone chat.

Land managers – from officials at the state level to federal managers with the US National Park Service and the Bureau of Land Management – increasingly are asking where their scarce conservation dollars can be put to most effective use at a time when global warming is changing the rules of the game.

Loarie's research team is providing a fresh way to do that, Dr. Inouye says.

For years, researchers have been trying to figure out how plants and animals would respond to global warming. But Loarie and his colleagues decided to ask the question from a different perspective: "What is the landscape's potential to buffer these changes?"

"It's really going from sounding the alarm over climate change to really trying to say: Look, some change is going to happen. How do we adapt to that change?" he explains.

The key, he says, is the speed of change.

To estimate that, the team used the Intergovernmental Panel on Climate Change's business-as-usual emissions scenario as the basis for tracking the pace of warming through 2100. Then they applied that to various habitats and even protected areas around the globe to get a sense for how quickly the climate regimes over these areas would be expected to change.

Globally, ecosystems will have to migrate at an average pace of nearly a quarter of a mile each year to keep up with shifting climate belts. That varies with habitat. Tropical and subtropical coniferous forests need only shift at a rate of roughly 260 feet a year to keep pace.

Mangrove forests, on the other hand, would have to shift at a rate of more than half a mile a year to keep up – highly unlikely given the unique conditions they require to thrive.

Mangroves "are not just rich in species, but they perform ecosystem services," says Lisa Graumlich, director of the University of Arizona's School of Natural Resources and the Environment. They help stabilize coastlines by sapping waves of energy, and they serve as nurseries for fish and shellfish on which coastal communities rely either as sources of food for subsistence living or as resources for commercial fishing.

While several ecologists hail Loarie's team's effort as significant, some say the work needs to expand to also take changes in rain and snowfall projections into account. Even then, the effect on some organisms can be counterintuitive.

Duke University ecologist Robert Jackson points out, for instance, that recent studies have shown that some ecosystems are more resilient than people previously thought. He cites a study in Tennessee, where researchers at the Oak Ridge National Laboratory divided an area of woods into three plots – one grew under existing conditions, one was subjected to drought conditions by channeling water to a third plot, simulating excessive rainfall.

The experiment, which lasted more than 10 years, found that mature trees in the stressed plots showed little change. Instead, the biggest effects were on saplings in the understory, suffered the ill effects of drought far more severely than the mature trees.

"That was a real surprise; that's a severe drought to do that for a decade," Dr. Jackson says.

"When organisms are established and long-lived as adults, they are much more capable of hanging on and surviving" than they are at earlier stages of development.

Indeed, the research team notes that their work doesn't account for how individual species might respond to the changes; instead, it refers to the speed of movement and what that speed implies for how long a particular patch of the globe will experience a given climate regime. So the numbers they give are relative measures of the pace of change rather than a hard and fast set of predictions.

Still, the numbers are sobering. The team, whose work appeared in Wednesday's edition of the journal Nature, estimates that plants covering nearly 29% of the globe's surface would have to migrate far faster than they did as climate changes coming out of the last Ice Age, if global warming proceeds as the IPCC's business-as-usual scenario plays out. Indeed, greenhouse-gas emissions have exceeded that BAU pace during the past decade.

Put another way, the researchers calculate that by the end of the century, fewer than 10% of today's terrestrial conservation areas will still experience today's climate somewhere inside their borders.

In the end, the approach Loarie and his team have devised "gives us a rational, transparent tool for altering us to where we need to think about investments" in land for conservation, Dr. Graumlich says.

Up to this point, there is "a wonderful hubris we feel about conservation – that if we could just national park systems or get more land into conservation easements that we're on a solution path that will work," she says.

"But climate change changes that game forever. We no longer can take a big fat Sharpie and make a circle on a map. We have to think about conservation in a much more dynamic way."

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