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Uprooted: how climate change may kick off an artificial migration of trees

Uprooted: how climate change may kick off an artificial migration of trees


Assisted migration could help save forests

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Whitebark pines
Whitebark pines
Wikimedia Commons

The National Park System is turning 100, and The Verge is celebrating with Wilderness Week: a look at the natural world, its freaky critters, and its future.

Whitebark pines are majestic trees with a whitish, often wind-curled trunk that grow up high in the Rocky and Sierra Mountains, in the Western US. They’re icons of Yellowstone National Park, where they provide high-calorie seeds for many animals, including grizzly bears that eat the seeds before hibernating. Some whitebark pines manage to live for a thousand years, but many of them are now dying.

The reason? Climate change. Warmer temperatures have allowed the mountain pine beetle to survive winters, exposing the trees to the voracious pest. And a vicious, lethal fungus is also on the attack. As a result, the USDA Forest Service estimates that 97 percent of the whitebark pine’s natural range will disappear by 2100 in the US.

Whitebark pines are icons of Yellowstone National Park

The strategy that might save whitebark pines in the long run is one that’s been discussed for decades among ecologists and is only now gaining traction: assisted migration. That basically means planting tree seeds in areas where they will be able to survive in the future. "If we keep the status quo and not move stuff around, we run the risk of losing populations or species," says Laura Gray-Steinhauer, who researches climate change adaptation strategies at the University of Alberta. The idea is that if we give trees a hand, they might fare better.

The problem is that trees, obviously, have a hard time migrating long distances on their own. Most trees don’t move at all (though some do), and they take a long time — sometimes even 30 years or more — to start producing seeds. Seeds don’t move on their own, either; they rely on the wind or animals like birds and squirrels to move around. While that might give an advantage to poplar seeds, which are light, it creates problems for large, heavy seeds like those produced by Torreya taxifolia, an endangered conifer.

"The problem with trees is they can migrate only very slowly," says Sally Aitken, the director of the Centre for Forest Conservation Genetics at the University of British Columbia. "They really can’t move quickly enough to keep up on their own."

Torreya taxifolia.
Torreya taxifolia.
Malcolm Manners/Flickr

Should humans step in? If only it were that easy. Many ecologists worry that translocated species might become invasive. All over the world, there are plenty of examples of trees and plants that were moved around — sometimes inadvertently, sometimes intentionally — only to become invasive and take over the native species. In the US alone, invasive plant species cost an estimated $120 billion a year, according to the Nature Conservancy.

Trees are also homes for a lot of creatures, including bugs and fungi. Moving trees means also moving this entire household of potential pests. Fungi can infect other plants and end up wiping out other trees. "We’re not moving species into vacuums, we’re moving them into communities where other species exist," says Mark Schwartz an ecologist at the University of California, Davis. "Engaging in the intentional moving of species for the conservation benefits is likely to have cases where we also cause unintended damage."

There’s also the question of where exactly the trees would go; most scientists don’t want an ecosystem’s survival to result in another one’s demise. In Sequoia National Park, for example, if you were to start moving sequoias up slope, you’ll most likely be planting them into wet meadows. Those meadows are also an endangered resource, says Schwartz. How do you decide what to keep and what to give up?

Some people are taking conservation in their own hands

Climate change has already altered how we approach forest management. Park managers will soon need to find new ways to protect trees, whether it’s with assisted migration or some other solution. "A national park has generally been a system where we take a hands-off approach to management," Schwartz says. "If anything trying to restore ecosystems to some historic, pristine state." But now, park managers are struggling to find new ways to preserve the nation’s forests.

Some people are taking conservation in their own hands. Connie Barlow, a retired science writer and amateur ecologist, launched her own assisted migration program in the US. Her goal is to save Torreya trees, which only survive in northern Florida in their native range and are listed as endangered under the Endangered Species Act. In early 2000, Barlow acquired Torreya seeds and seedlings from botanical gardens and nurseries, and began planting them in private forests and yards in North Carolina. Since then, she’s also planted Torreya trees in Virginia, Tennessee, Ohio, and New Hampshire, with the help of other volunteers.

"Citizens need to step forward and we’ve shown we can do it," Barlow says. "What’s undeniable now is that climate change is happening so rapidly ... that even common species are going to have to be moved by humans, intentionally."

Sequoia trees.
Sequoia trees.

Some ecologists, however, are wary of her actions, and accuse her of acting too fast, without conducting the proper research. "I thought it was very premature," Schwartz says. "We have no indication yet that management will be able to save the species within its native range. It is declining toward extinction." Others support what Barlow’s doing. Torreya trees are very "low risk" — their seeds don’t disperse easily, so they’re not likely to become invasive species, says Gray-Steinhauer at the University of Alberta. "As far as a conservation effort, it’s appropriate," she says. "It’s a good strategy."

In Canada, some assisted migration programs are already underway, but they’re done a bit more cautiously. In British Columbia, for example, the western larch is being migrated north, outside of its range. But when an area is planted, only 10 percent of the trees can be western larch, says Aitken. That’s to be on the safe side: if the western larches don’t survive, the other trees will eventually occupy their space. If they do, they won’t be able to take over.

"Doing nothing, we lose the species."

In the US, forest managers are considering a less controversial form of assisted migration that has to do with seed selection, according to Christopher Woodall, a research forester at the Forest Service. Instead of moving trees north, forest managers are selecting seeds of the same tree species that live in warmer climates and are therefore more resistant to droughts. For example, there’s the ponderosa pine, a pine species that’s widely distributed in the US. Some, in the northern Rocky Mountains, grow in wet areas; others, like those in New Mexico, live in pretty dry ones. If climate change makes rains less likely in the wet areas, it’s possible to plant seeds of pines that live in dry areas. These kinds of variations between members of the same species may chart a path forward for ecologists. "I think the forest management community is starting to think more about what they’re planting," Woodall says.

Whatever strategy is used, most conservationists agree that something needs to be done. Saving trees means much more than just saving forests: it means saving the habitat where many other species live in, it means saving the roots that regulate water flow, and the mechanisms that take in carbon dioxide and create the oxygen we need to live. "Doing nothing, we lose the species," says Gray-Steinhauer. "Doing something, we take a risk but we don’t know for sure. So you have to weigh out those pros and cons."