Foresters hope 'assisted migration' will preserve landscapes as the climate changes

Emma Jacobs

May 18, 2022 / 9:01 am

Forestry technician Grace Smith has spent the spring working 10-hour days, planting trees in the woods of the Silvio O. Conte National Fish and Wildlife Refuge in Vermont.

With 200 to 300 saplings a day to resettle in test plots before the weather gets too hot for young trees, Smith and her colleagues use dibbles — long, pointed tools with handles, to open holes in the ground.

"They're super handy," Smith says, "to be able to get these roots deep enough down."

The saplings include a variety of species chosen to see if they will increase the forest's resiliency. One variety of red spruce, especially chosen for its origins in the mountains of West Virginia, will become a test of what scientists call "assisted migration," introducing populations from warmer areas to northern latitudes projected to become hotter and drier in a changing climate.

"Grace, you got trouble over there," warns the refuge's forester, Jeremy Goetz, as a deer appears on the far end of the partially-cleared test plot.

Besides hungry deer who will snack on unprotected saplings, the refuge also provides habitat for grouse, Canada lynx, moose, and other bird species with declining populations, including a songbird with a bright yellow stomach called a Canada warbler.

But the forest's history has left it vulnerable.

Climate risks heightened in a one-species forest

Goetz points out ruts left by heavy timber harvesting equipment decades earlier, when this land used to belong to a paper company, "The machine that they would use to pull the logs out." A closer look at the trees reveals an unusually uniform landscape of young, balsam fir.

If the increasingly hot and dry weather, or new insects, start to kill the balsam fir, that could mean a lot of dead trees across this landscape. "With climate change," says Tony D'Amato, the director of the University of Vermont's forestry program, "the broadest things we want to maintain are the functions of forest that are so important, so it's clean air, it's carbon sequestration, it's water filtration, it's bird habitat."

While the saplings his team is planting in partnership with the refuge include a variety of species grown in tree nurseries, including pine, cedar and hemlock, he's most excited about the red spruce. He says the climate the seeds came from, in the Central Appalachians, looks a lot like what models predict for this region of Vermont by about 2070.

Katy Barlow, of The Nature Conservancy, which produced the seedlings, says red spruce already grows in Vermont, but will have small genetic differences from the same species found further south.

"The main portion of the red spruce populations are up in northern New England. But in each of those places, these populations have adapted to their particular climate," Barlow says.

Genetic analysis has identified differences in the start and end point of the growing season for the West Virginia red spruce. If trees optimized for the weather patterns of West Virginia can survive in Vermont now, an established population could give this forest a head start in adapting to its future climate.

Foresters have experiments underway around the country in "assisted migration." This term actually covers a pretty wide gamut of activity, from, in this case, moving a genotype within a tree's existing range to introducing an animal somewhere its species has never lived before.

Climate change is preceding faster than forests can keep up

"Thinking about actively moving species around is a little, well a lot uncomfortable for us," acknowledges Abe Miller-Rushing, the science coordinator for Acadia National Park in Maine. "What might be the kind of unintended consequences? What diseases might we unintentionally move around if we move species around?"

He says, historically, the Parks Service has preferred hands-off management and modeled restorations on past conditions. In Acadia though, he noted, not intervening as warming takes place could mean the park's iconic evergreen forests get replaced by shrubland, dominated by invasive bushes.

"Typically, in a warming environment like this, we would expect trees from the south, things like oaks and hickories to move up into the park, but the climate is changing faster than those species can keep up with," Miller-Rushing explains. Then, too, "we've put a lot of obstacles in their way," he says, fragmenting the landscape with cities, highways, and suburbs.

Assisted migration "might be the best bad idea that we have"

Last year, the National Park Service published a guide for staff considering assisted migration. Miller-Rushing helped write it, alongside Mark Schwartz, a researcher at The University of California, Davis. He says forest managers attempting to shift species or genotypes face a lot of uncertainty.

"It turns out though," he says, assisting with relocations, "might be the best bad idea that we have. And, as a consequence, we may need to engage in more and more."

More data from experiments like the one in Vermont will help inform decision-making.

"There's always that challenge too, it's like the personal versus the scientific," muses D'Amato, the research scientist. He would not want to see familiar species like sugar maple or red spruce disappear from the northern forests he works in, he says. "Personally, I'd be pretty upset."