
Photo Credit: Andrew Studer / American Forests
WHEN MOST PEOPLE THINK OF MIGRATION, they tend to think of wildlife, like humpback whales, monarch butterflies or arctic terns, traveling vast distances to find the climates they need to survive and thrive. Through the dispersal of their seeds, trees move, too, but much more slowly — only from generation to generation, and they’re limited by how far their seeds can travel by wind, water or hitching a ride with another creature.
“They’re essentially relying on each new generation being able to move a little tiny bit,” says Dr. Libby Pansing, American Forests’ director of forest and restoration science.
Plants have long used these measured movements to respond to environmental conditions — for example, resting in refugia during ice ages and then slowly expanding their ranges as the glaciers retreat. “But that happened over thousands and thousands of years. Climate change is happening now, very, very quickly, on the order of decades. And that puts a time crunch on those species to make the march to new locations where the environment is ideal,” Pansing says. The fear is that many tree species will not have sufficient time to make those slow movements and they will increasingly lag behind the climate they are adapted to.
To help forests keep pace with climate change, researchers and forest managers are looking at using a strategy known as assisted migration, which provides trees with a climate-informed “nudge” across the landscape. Essentially, assisted migration involves taking a seed or seedling from a warmer location and planting it in a new location that, due to climate change, will experience warmer conditions in the coming years, helping to ensure the tree will survive and reproduce — spawning the next generation of resilient forest.

Photo Credit: Julia Twichell / American Forests
There are several assisted migration strategies that forest managers, geneticists and other experts are using to move trees to areas where they will thrive in the future. The first — and most conservative — approach is called assisted population migration.
With assisted population migration, populations of trees are moved within the range where they currently grow. An example is cultivating a Ponderosa pine seedling that is thriving at a relatively low, warm elevation and planting it among other Ponderosa that are growing in a slightly higher and cooler elevation 1,000 feet upslope from its place of origin — where conditions are expected to warm. The goal is to plant the upslope area with trees already adapted to hotter, drier conditions so they can better withstand the drought and extreme temperatures that are likely to affect the higher location in the future.
“You’re not moving it into a location where that species isn’t already present,” Pansing says. “They currently grow there. You’re just moving those seed sources a little bit so that potentially those seeds are better adapted to the future conditions at the location where you’re doing outplanting.”
Two additional approaches to assisted migration are assisted range expansion — planting a particular species just beyond the current edge of its range, into adjacent areas where it doesn’t currently grow but would be expected to migrate into in time — and assisted species migration, which involves moving species to establish in new areas where they do not currently grow and would not likely be able to migrate to naturally, but will be acclimated for projected future climate conditions.
American Forests is supporting several projects with partners like the U.S. Forest Service and other stakeholders that are primarily studying assisted population migration. The partners are focused on discerning which seedlings may already be adapted to certain climactic conditions, and then doing selective planting as part of a wider effort to make forests more resilient to climate change.

Photo Credit: Courtesy of Bryan Reatini / U.S. Forest Service
The need for this type of work is already clear in places like the national forests in southwest Oregon, where the landscape is undergoing dramatic changes, says Dr. Bryan Reatini, a Forest Service geneticist based in Roseburg, Ore. Hotter, drier temperatures have already arrived, and so have massive wildfires, like the Archie Creek Fire, which burned more than 130,000 acres in the North Umpqua watershed in 2020.
Reatini is developing reforestation strategies that use assisted population migration to gently move seedlings of species including Ponderosa pines and Douglas-fir to nearby locations — helping ensure the species’ survival on the landscape. “Populations of forest tree species are pretty closely adapted to their local environmental conditions,” Reatini says. “Let’s say there’s a population of Douglas-fir that occurs naturally in southwestern Oregon. That population has experienced relatively hotter and drier conditions during the last 100,000 years, relative to a population of Douglas-fir further north.”
Planting a seed from these drought-adapted southern populations in a slightly different location — a place that is starting to experience hotter and drier conditions due to climate change — could mean that the growing tree will already have some resilience to changing environmental conditions. But, as a Douglas-fir, it would still belong in its new setting. “We’re not changing the ultimate range of the species,” Reatini says. “That type of movement would happen naturally,” albeit over a longer time scale.
Reatini and his colleagues are considering how to plant trees within their range to better track a rapidly changing climate. To do this, forest managers first need to know what conditions trees experienced on the land historically, their current growing conditions, and what the future might look like for specific areas of the forest. One of the instruments they use is called the Seedlot Selection Tool, which forest managers can use to determine which areas have similar climate profiles and source seeds that are well suited to their planting sites. They can also use this information to ensure that seedlings are not transferred beyond the range of climate conditions the parent trees are adapted to.
Reatini has been developing additional tools to understand how the climate of individual forests has changed from the past to the present, and projecting how they might continue to change in the future.
“Not all forests are changing at the same rate,” he says. And even within a forest, some parts experience greater shifts than others. Reatini developed a tool called SEED to help forest managers quickly do a climate match for any seed that is already available in the Forest Service’s seed collections. The instrument has already enabled rapid, large-scale climate matching analyses that are guiding seed-sourcing efforts for reforestation on Oregon’s Fremont-Winema National Forest.

Photo Credit: Andrew Avitt / U.S. Forest Service
Reatini and his colleagues are also setting up experimental plots to test assisted migration as part of a larger effort called the Experimental Network for Assisted Migration and Establishment Silviculture. This ongoing effort is a collaboration between the Forest Service’s Pacific Northwest and Pacific Southwest research stations, and Forest Service Regions 5 and 6. American Forests is one of the supporters of this project, which is establishing a growing network of more than 30 sites in Washington, Oregon and California. The goal is to help reforestation projects thrive, says Forest Service Conservation Geneticist Dr. Jessica Wright, one of the lead principal investigators for the effort.
“Any tools and any information we can provide to land managers that might improve the success of their reforestation is really important,” she says.
To do this, researchers are looking at both what seeds to plant and how to plant them. At each Experimental Network for Assisted Migration and Establishment Silviculture site, they will study seed sources representing different projected climate scenarios — early 21st century, mid-century and end of century — along with a local seed source to compare current and future conditions to what the area experienced in the past. Seedlings from each seed source will receive different treatments — such as removing surrounding plants to reduce competition for water and sunlight, or planting seedlings grown in containers versus bare root — so that researchers can learn how to help seedlings better survive.
Wright, who is based at the Pacific Southwest Research Station in Placerville, Calif., started thinking about the importance of these planting decisions in reforestation at an event where forest managers told her they needed her research and expertise on tree genetics to help guide planting for climate resilience.
“It was a call to action for me,” Wright says. The effort, she says, “is not cheap, and it is not easy. So, conducting research to help inform reforestation project decisions — I think it’s important.”
One of the planting sites that Wright is studying is in the burn scar of the Caldor Fire, a 2021 wildfire that burned more than 220,000 acres in the Eldorado National Forest and surrounding areas. American Forests planted this study site in 2023. This fall, Wright will take the first survival measurements for these trees, along with tagging and measuring new seedlings in five additional Northern California sites planted last spring. Wright thinks they will have data about how seedlings can better thrive in climate change in the next five years. Knowing more about seedlings is critical to setting up future forests for success.

Photo Credit: U.S. Forest Service
“Early survival and growth are really important in these trees’ long-term development,” she says. Seedlings need to be adapted to both the current and future environments to survive and grow into resilient, productive forests.
Getting a fuller picture of how assisted migration might help forests will take much longer. “Trees live for hundreds of years, so it may be 15 to 20 years until you get results,” says Dr. Andy Bower, a climate adaptation specialist with the Forest Service’s Office of Sustainability and Climate.
Still, the effort is worthwhile, he says: From ailing Douglas-fir and western redcedar in the Pacific Northwest, where Bower is based, to the boreal forests of the upper Midwest, “we’re seeing these impacts of climate change over and over across the country. If we don’t start to do something, that’s just going to continue.”
The west isn’t the only place where forest managers are starting to explore assisted migration. In Minnesota, the Superior National Forest developed the first assisted migration plan in the National Forest System, which aims to help northern boreal forests that are experiencing the leading edge of climate change.
People may be concerned with the idea of moving species, particularly during a time when invasive species have wreaked havoc on already-fragile ecosystems. That is one reason that the Experimental Network for Assisted Migration and Establishment Silviculture primarily focuses on assisted population migration, which does not move species out of their existing ranges.
“Those are legitimate concerns,” Bower says, “but the risk of a species becoming invasive is not a risk if you’re moving species within its range.” And with the accelerated pace of climate change, in Bower’s view, moving forward with multiple approaches to help forests survive is the only option. “Sometimes the risk of doing nothing is greater than the risk of doing something.”
Through studying assisted migration, researchers across the west coast have already committed to doing something to help forests weather changes ahead — and offer hope for the future, Pansing says. “We can use these spaces as learning laboratories to see what’s going to work and to help us to really better understand how to respond to the climate crisis.”
Cameron Walker writes from California and is the author of the children’s book “National Monuments
of the U.S.A.”