The New York Times, September 18, 2014
The whitebark pine grows in the high, cold reaches of the Rocky and Sierra Mountains, and some trees, wind-bent and tenacious, manage to thrive for more than a thousand years.
Despite its hardiness, the species may not survive much longer.
A lethal fungus is decimating the pines, as are voracious mountain pine beetles. Making matters worse, forest managers have suppressed the fires that are required to stimulate whitebark pine seedlings.
Half of all whitebark pines are now dead or dying. In 2012, Canada declared the tree an endangered species, and in the United States it is currently a candidate for listing under the Endangered Species Act.
Now the tree faces a new threat: a swiftly changing climate. Temperatures are rising, and Forest Service researchers estimate that 97 percent of the whitebark pine’s natural range will disappear from the United States by 2100.
Traditionally, conservation biologists have sought to protect endangered plants and animals where they live, creating refuges where species can be shielded from threats like hunting and pollution. But a refuge won’t help the whitebark pine, and so now scientists are pondering a simple but radical new idea: moving the trees to where they will be more comfortable in the future.
It’s called assisted migration, and the debate over its feasibility comes as biologists everywhere begin to reassess their tactics and the impact of climate change on endangered species.
“What we were doing wasn’t going to protect them in the long term,” said Bruce Stein, director of the National Wildlife Federation’s climate adaptation program.
Dr. Stein and his colleagues recently published a 272-page guide to “climate-smart conservation,” offering advice on how to make ecosystems more resilient.
Southern Utah, they noted, is bracing for droughts that may endanger many species. In response, conservation biologists are introducing beavers into the region. The water trapped in beaver dams may support many species and refill underground supplies.
When the Forest Service drafted a plan for restoring the whitebark pine in 2012, officials didn’t just take killer fungi and hungry beetles into account: they also pondered how the trees could best withstand a warming climate.
Their plan calls for rebuilding whitebark pine populations by planting seedlings and setting controlled fires. Healthy forests of whitebark pine, they argue, should be better able to withstand climate change. The trees may even spread northward as higher latitudes develop a suitable climate.
“We feel the bottom line is to help whitebark respond on its own to climate change,” said Diana F. Tomback, director of the Whitebark Pine Ecosystem Foundation.
But what if the climate warms too quickly for the trees to respond? Even as the species creeps northward a few miles, it may lose huge swaths of suitable territory to the south. The solution, some conservationists say, may be to help the trees claim new territory more quickly.
Assisted migration remains mostly hypothetical. But in 2007, Sally N. Aitken, a geneticist at the University of British Columbia, realized that she could test the idea.
Dr. Aitken discovered that the northwestern corner of British Columbia had the right climate for the whitebark pine. But for reasons that weren’t clear, the trees didn’t grow there. Climate projections indicate that region should still be good for the trees in a century.
So Sierra McLane, a graduate student working with Dr. Aitken, hiked into the remote mountain ranges of British Columbia and planted 18,000 whitebark pine seeds, some as far as 500 miles beyond the tree’s current range. About 20 percent of the seeds germinated. Seven years later the trees are still growing, even at the northernmost sites.
“I’d say it really is a proof of concept,” said Dr. Aitken. “That leads to the question, ‘Should we move whitebark pine?’ But that’s not a biological question.”
Indeed, it’s an ethical question that triggers fierce debate in conservation circles.
Critics have warned that assisted migrations like this could prove to be expensive failures. Even if they succeed, the rescued species may become invasive pests in their new habitat.
Brendon Larson, an environmental social scientist at the University of Waterloo, and Clare Palmer, an ethicist at Texas A&M University, argue that assisted migration of the whitebark pine poses little risk because the species grows so slowly.
In a paper to be published in the journal Environmental Values, Dr. Larson and Dr. Palmer conclude that the pros outweigh the cons. Whitebark pines prevent soil erosion and, by trapping snow in the winter, help foster a steady water supply for the valleys below them.
And over a hundred species of animals, including bears and birds, depend on the whitebark pine for food and shelter. “It just makes sense to try to maintain them as best we can, and assisted migration could well help with that,” Dr. Larson said.
Dr. Tomback doesn’t rule out assisted migration, but she has many doubts. To spread their seeds, whitebark pines depend on birds called Clark’s nutcrackers. If the trees are to survive in the long term, conservation biologists also will have to figure out how to establish the birds in their new range.
“Short of tethering them, what keeps them there?” Dr. Tomback asked.
Robert E. Keane, an ecologist at the Rocky Mountain Research Station, believes it would be wiser to find trees that can resist the fungus and use them to plant new forests, which should be maintained with fires.
“In my mind, employing assisted migration is probably the worst thing we can do with any valuable restoration funds,” he said.
A less controversial variation of assisted migration involves moving plants or animals within their existing range.
In a species like the whitebark pine, each population may have evolved adaptations to its local environment, and trees on the southern edge of the range may have genes resistant to heat.
Moving some of the southern trees northward could give northern populations the genetic resources to thrive in a warmer climate.
Influencing the evolution of a wild species in such a way strikes many biologists as a perilous step. But most agree that the choices we’ve left for ourselves are far from ideal.
Mark W. Schwartz, an ecologist at the University of California, Davis, said: “You see everybody getting more comfortable with the idea that the future is going to look very different from the past.”
Copyright 2014 The New York Times Company. Reprinted with permission.