Helping Trees Move Up

This story is part of The 89 Percent Project, an initiative of the global journalism collaboration Covering Climate Now. This story was originally published by Earth Island Journal.

A Douglas fir seedling stretches its spindly green bristles into the Gifford Pinchot National Forest, in Lewis County, Washington, its roots winding into the soil nearly 200 miles north of its origin in the Willamette and Siuslaw National Forests of Oregon. Despite a long journey to the slightly cooler canopy of Washington’s towering western hemlocks and Engelmann spruce, researchers predict the transplant will adapt to its new surroundings sometime in the middle of the century while its family of firs back in Oregon stay rooted, sweltering in a warming climate.

The sapling came to its new home on the outer reaches of its historical range through the helping hand of Andrew Bower, a climate adaptation specialist with the United States Forest Service, as part of a growing list of experimental trials conducted by the agency. For the forester, replanting the small but hardy fir in a new location isn’t just about securing the fate of one seedling, but about giving forests their best chance of survival.

“The impacts of climate change are acute, trees aren’t able to withstand these extremes,” Bower says, citing the recent heat dome that blasted through the northwest in 2021. The record-breaking temperatures left tree leaves scorched, had needles dropping from hemlocks, and killed many young saplings. “The goal is to figure out what works best for establishing and growing the healthy, resilient forests of the future,” he says.

While the lucky young Douglas fir caught a 200-mile lift with the Forest Service, trees do naturally move as environmental conditions shift, adapting and migrating in a slow process that takes decades or even centuries. In a rapidly warming world, these leafy species are having a hard time adjusting. To escape the heat, trees are predicted to seek better real estate up north in cooler climes. The yellow birch in the eastern U.S. is expected to jump the border into Canada while seeds from Oregon and Washington have grown successfully in northern British Columbia. These changes happen gradually since, unlike animals who can move to higher elevations on their own, trees can’t uproot themselves. This is where the human-assisted movement of species comes in.

Experimental projects by the Forest Service known as “assisted migration” are testing the relocation of trees, moving young seedlings from where they are currently growing to where climate data predicts they will grow.

“As the climate is changing, we’re finding that local populations are not necessarily the best adapted to their environment,” Bower says. “By establishing forests that are adapted to future climates, those future forests will be self-sustaining because the trees will be adapted to that climate. They will reproduce successfully without us having to go back and replant.”

To do this, projects select populations of a particular tree species from an area that is usually warmer (typically lower in elevation or farther to the south), meaning it is genetically evolved to thrive in that environment, and move it into a higher elevation to establish a forest that is better suited to survive as temperatures increase. Trees on the move cover a range of species from the sub-boreal spruce of the John Prince Research Forest in British Columbia, the oak and maples of the Ohio Hills, and the pines of the ​​Chippewa National Forest in Minnesota.

As interest in these projects has grown, a clear distinction between three types of assisted migration has been established: assisted population expansion (the process previously described) — moving a plant to new locations within the species’ historical range; assisted range expansion — moving a plant species just beyond its historical range by mimicking natural seed dispersal; and assisted species migration — moving trees to an entirely new area that would normally be inaccessible by natural dispersal.

Bower clarifies the Forest Service is not doing assisted species migration, nor does it advocate for moving any species around on a large scale. These adaptations are happening within the tree’s existing range, or slightly beyond. Current forestry practices are also confined to small experimental research trials, looking at species in new areas to see how they perform or for conservation purposes to aid threatened and endangered species.

“People often immediately go to curiosity and concern about moving species around on the landscape,” says Bower. “Any work the Forest Service is doing is to preserve a species, whether from insects, disease, or the pressures of climate change where it may need to be planted outside of its range to survive.”

Many of these innovative projects are happening under the Canada-U.S. Desired Regeneration through Assisted Migration network. In addition to experimental trials by the Forest Service in the Pacific Northwest, there are several such projects underway as part of the international Adaptive Silviculture for Climate Change (ASCC), a collection of experimental silvicultural projects throughout different forest ecosystem types in the U.S. and Canada. Established in 2012, these projects, in over a dozen sites, follow a similar framework but are tailored to their local environment.

Three of these sites are located within different types of mixed conifer forests in Colorado and were selected due to their unique ecosystems. They include a lower-elevation, mixed conifer forest in the San Juan National Forest in western Colorado, a higher-elevation lodgepole pine and spruce site in the north-central portion of the Taylor Basin, near the Taylor Park Reservoir, where researchers are predominantly looking at the importance of water flow and snow on overall forest health, and in Colorado State Forest, which is the highest-elevation site of the three with a similar lodgepole and spruce fir forest type as Taylor Basin.

In addition to assisted migration, these projects are looking at tools that may help trees survive climate impacts like more frequent fires, longer growing seasons, and drought. For all three sites, workshops involving stakeholders took place before treatments were drawn up, following a “resistance, resilience, and transition” framework, essentially a sliding scale of climate change adaptation.

“Resistance is more or less trying to keep things the same, resilience is allowing some sort of change so the forest can bounce back, and transition is transforming the ecosystem to something else, which would come after a disturbance,” says Mike Battaglia, a research forester with the U.S. Forest Service Rocky Mountain Research Station and the project manager for the Colorado sites.

A resilience treatment at the San Juan site will involve creating openings in the canopy of lodgepole pine, ranging from half an acre to several acres, and planting Douglas fir and limber pine in those openings, Battaglia says. Researchers will then look at how those species interact and how it may change aspects of the ecosystem such as snow accumulation. In Taylor Park and Colorado State Forest, a transition treatment will involve bringing in a lower-elevation species like ponderosa pine to aid in transforming the forest into an upper mountain mixed conifer forest rather than a subalpine forest.

All three project sites have planned prescriptions and will soon start the planting process, which will be monitored extensively for a variety of factors such as tree survival and growth, pollinator abundance, and nutrient cycling. In addition to data collected on the trees, researchers will monitor a whole range of things within the ecosystem.

That includes snowpack, Battaglia says. “Snow helps prevent fires and as we’re seeing a lot of wildfires happen earlier in the season, being able to hold more snow is important. We’re going to be measuring how the snowpack changes through time and with these different treatments.”

The Forest Service also hopes researchers can utilize the project sites for further scientific lines of inquiry and look at areas such as water flow, soil, drought, the spread of disease, and more.

Trees grow slowly, especially in high alpine environments, and these sites will provide an important hub for researchers to compile long-term projects essential to understanding climate change’s wide-ranging effects. (In addition to the U.S. Forest Service, projects under the ASCC initiative are supported by a variety of sources, including universities and state forestry agencies, so they haven’t yet been impacted by the Trump administration’s funding cuts. But there are concerns that budget cuts to the Forest Service research programs could have an impact down the line.)

Assisted species migration has sparked controversy around the potential unintended consequences of reconstructing our natural world. Patrick Martin, an ecologist and professor at the University of Denver, says when it comes to assisted migration there are generally three categories of risks. The first comes down to practicality — it’s not guaranteed a seedling will thrive in its new environment, bringing up concerns around wasted effort and resources as these projects can be costly. The sourcing of seedlings and legalities when it comes to moving trees across political borders that may include numerous jurisdictions are potential barriers as well.

As for the other two areas of risk, Martin says there is the possibility the species could have an unintended impact on its new environment such as spreading disease, becoming invasive, or outcompeting existing species for resources like water or sunlight. The third risk would be the effect on the species’ original community, degrading and weakening an existing system by moving seedlings elsewhere. “Species could also hybridize and create a new species,” says Martin. “Hybridization may not necessarily be a bad thing. There is hope by bringing southern populations in, they might hybridize with local species making them more vigorous.”

Battaglia says some challenges specific to the Colorado sites could include a seedling not being as adapted to the cold it may experience in a higher elevation along with a shorter growing season and more opportunity for frost. This is often called “maladaptation” and trees can start growing too early, leaving them vulnerable to damage or the hungry mouths of passing deer or elk, which could impact the ability to generate offspring. Additionally, “trees are grown in a specific soil type and it’s not clear whether we should also be bringing the soil along,” Battaglia says.

Martin emphasized that any assisted migration projects must take sensible precautions and that nobody is advocating for grabbing seeds and throwing them around on the landscape.

“There is deep philosophical concern about playing with nature,” he says. “If no one was doing it then maybe there would be grounds for that, but it’s already happening so why not give those trained to advocate for nature a chance to do it well.”

On the flip side, he says, some criticize these projects for moving too slowly and cautiously. Given the sobering reality of a heating planet, there aren’t many alternatives to securing the future of trees.

In addition to projects like assisted migration that facilitate change and help species adapt, there are two other courses of action, says University of Colorado Boulder ecologist and associate professor Laura Dee: accepting change and letting nature do the best it can, which would likely mean letting many species die, or resisting change.

“Resisting change would mean looking at local threats and what actions we can take to identify places that might be less vulnerable to losing the species in the future,” Dee says. “This would include prioritizing, protecting, or managing those places to keep the species where they are.”

Managing local threats such as drought or insect diseases may be an uphill battle in many cases as climate change fuels the spread of these local conditions. Martin also noted that while investments can be made to save individual tree species, especially those that may have a direct benefit to people, that’s much harder — if not impossible — to do on a forest scale.

“There’s been a growing recognition in science and conservation that managing historical conditions and baselines is becoming increasingly intractable,” Dee says. “We need creative solutions.”

There’s also a critical need to take a holistic approach to these projects because, as Dee explains, trees aren’t single entities, but connected to a complex ecosystem that supports various other organisms and species. In her work locally in Boulder, Colorado, the ecologist is researching the impacts of drought on native prairies, looking at how adding drought-adapted species from other places could help provide a buffer for those struggling species.

“There are cases where we have woody encroachment into prairies and that changes the dynamics of the ecosystem from types of birds to carbon flow and water use,” Dee says. “If we think about assisted migration as a single objective versus a diverse set of objectives, that’s when we could have those unintended consequences.”

These projects aren’t just for the tree’s sake, but are intricately connected to our own thriving. The cascading effects of a declining forest will impact clean water, recreation opportunities for people, and wildlife habitat, and ultimately hasten global warming, as less wood production means less carbon uptake and storage. For example, Taylor Park sits at the headwaters of the Taylor Reservoir, and a thinning forest could increase sediment and pollutant runoff into the water source utilized by local farmers. Similarly, a declining forest in the high alpine basin could impact communities that rely on the water source in the dry Colorado environment.

As researchers work to understand how the forests of the future must adapt, they weigh the real risks that come along with introducing any new species into an environment.

“We need to be aware of the risks of not doing things and the risks of doing things to make sure we’re making a balanced choice,” Bower says. “There are risks, but there’s also ways to minimize those risks. That, in my mind, is less risky than not doing anything at all.”