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Can Flamethrowers Help Trees Migrate?

Trees shift range very slowly without an assist from human intervention
longleaf pine on fire


LONGLEAF PINE FORESTS NEED FIRE: Fires remove competing woody vegetation and release nutrients, allowing the rich diversity of plant and animal species found in longleaf ecosystems to thrive. As temperatures rise in a changing climate, wildfires are expected to increase, making the longleaf pine a good bet for the future.
Credit: John Maxwell for USFWS via Wikimedia Commons

About a year ago, Nature Conservancy foresters started a small experiment on a 20-acre field in eastern Maryland, planting about 1,000 longleaf pine seedlings just north of their natural range.

And on Wednesday, the conservancy teamed up with a Fish and Wildlife Service crew to set its experiment on fire. A team of 16 men and women sporting fire-resistant clothing and drip torches methodically set the area alight, and soon flames engulfed everything that grew there. A few hours later, the Nature Conservancy's preserve was nothing but a smoldering field of black ash.

They did it on purpose, of course—fire is an important part of the longleaf pine's life cycle. But if it weren't for climate change, it's likely that the land wouldn't have been burned at all.

The natural range of longleaf pines extends only to southern Virginia, explained Dave Ray, a conservation forester with the Maryland and D.C. chapter of the Nature Conservancy, who is leading the project. But due to climate change, the range of temperatures where longleaf pines can comfortably grow is shifting north.

Plants and animals have been adapting to natural changes in climate for millions of years, Ray said. But he added, "The rate that is happening now is likely outpacing how quickly species could move ... particularly sedentary species like trees."

To give the longleaf pine a head start on global warming, Ray is overseeing one of the Nature Conservancy's first tests of "assisted migration," or the introduction of a species to a new climate that is expected to be more favorable in the future.

Wednesday's controlled burn on Maryland's Delmarva Peninsula provides a small example of the kind of human intervention that might become more necessary—and more common—if forest ecosystems are going to survive climate change.

Slow-moving tree species have a long way to go
It's important to note that longleaf pines were in trouble long before global warming became an issue. Prior to the arrival of European immigrants, longleaf pine forests dominated the landscape of the U.S. Southeast, blanketing about 91 million acres of land.

But several centuries of human development have devastated their populations and threatened many of the animal species that depend on them like the endangered red-cockaded woodpecker. Today, about 4.4 million acres of longleaf pine forest remains, up slightly from its lowest point at 2.9 million acres in 1995 thanks to aggressive conservation efforts, explained Robert Abernethy, president of the nonprofit Longleaf Alliance in Andalusia, Ala.

"We're coming back; it's a success story," Abernethy said.

But according to Ray, climate change could jeopardize this success story. A 2013 paper in the journal Forest Ecology notes that based on current climate projections, plant species in general are going to need to migrate up to 16,400 feet each year—a distance about 10 times greater than plants are naturally capable of moving, on average.

Long-lived species like longleaf pines are in even more trouble because their life cycle is much slower, Ray explained. Additionally, human development has fragmented many of America's forests, which makes it more unlikely that trees can naturally venture north to adapt to higher temperatures.

According to R. Kasten Dumroese, research plant physiologist with the Forest Service's Rocky Mountain Research Station in Moscow, Idaho, and co-author of the Forest Ecology paper, there are few other examples of assisted tree migration in the United States.

This is because the process of assisted migration is "really extraordinarily complicated," he said, as foresters must take tree genetics, future climate models, soil moisture capacity and myriad other factors into account.

However, Dumroese added, "My gut feeling is that we will be adjusting seed sources to keep up with shifts in climate in the future—I don't think we'll have any choice if we want to maintain productivity of our forests."

Healthy sprigs under the ashes
Before Wednesday's burn began, it took Ray a few minutes to find one of his longleaf pine seedlings, which were shipped up from a North Carolina nursery and planted last April. The seedlings don't look like much—just little sprigs of needles extending about 6 inches from the ground, barely distinguishable from tufts of grass growing around them.

Standing among his crew of FWS and AmeriCorps firefighters, FWS fire management officer Art Canterbury explained they were burning the fields to "try to get some heat on the pines, reduce the competition around them and hopefully get them to release."

Longleaf pines don't compete well with other plant species, Ray explained. But when fires regularly move through their habitat—as they did long ago in the lightning-prone Southeast—they are able to establish their roots and grow. The Nature Conservancy plans on burning the area on a regular basis to keep the longleaf pines healthy.

This week's burn was the first for the conservancy's fledgling longleaf forest. The flames lapped across the field in an impressively well-managed line under the FWS fire team's careful supervision. Every so often, one of the longleaf pine's primary competitors, a loblolly pine tree, was engulfed in a whoosh of flames.

After the smoke cleared, Ray wandered into the field to find his seedlings again, which were even harder to pick out under the ash. But after a while he pointed out one or two that escaped the mini-inferno unscathed.

The burn was dubbed a success, but only time will tell whether a climate-ready longleaf pine forest will successfully grow there, Ray warned—"It's kind of a test of concept," he said.

But if in a few decades the seedlings grow into a forest, Ray added, "this would be one example that people could say, 'Hey, it works!'"

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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