Trees are losing ground due to climate change and trees are disappearing from hotter areas. Nevertheless, they are not moving into cooler, wetter climates, said a new Colorado State University study. This suggests forests are not regenerating fast enough to keep pace with rising temperatures, wildfires, and disease outbreaks.
The study focused on trees in the interior US West. It stated that the trees here are losing ground due to climate change. The scientists analyzed national forest inventory data from 25,000 plots across the U.S. West. They expected trees to shift into more suitable conditions as their existing habitats became too warm. Yet, most of the 15 common tree species studied showed no expansion into these favorable regions. This indicates that forests may require human intervention to sustain certain species.
ROLE OF WILDFIRE AND OTHER DISTURBANCES
Using 30 years of disturbance data, researchers examined whether wildfires could facilitate tree movement by eliminating competition. The findings were surprising. Even in burned areas, trees were not migrating to cooler zones as expected.
“Trees can only function within certain climatic tolerances,” said lead researcher Katie Nigro. “We thought we’d see more shifts into cooler zones, but that wasn’t the case.”
NEED FOR ASSISTED MIGRATION
The study, published in Nature Climate Change, highlights the need for human-assisted tree migration. As climate change accelerates, tree species may struggle to regenerate without intervention.
“Forest managers need to know where certain trees can still thrive. They also need to identify where these trees might need help,” Nigro explained.
TREE SEEDS FACE AN UPHILL BATTLE
Increasing wildfires and insect outbreaks further complicate tree regeneration. Seeds face significant barriers to moving uphill to cooler areas, including gravity and unsuitable conditions.
“A lot needs to align for a tree to establish in a new climate,” said co-author Monique Rocca. “This study helps determine where trees can persist on their own versus where intervention is necessary.”
SOME TREES ADAPT BETTER THAN OTHERS
Four tree species showed continued regeneration despite climate change and disturbances. Three of these species are rare, making their response harder to assess. The fourth, Gambel oak, is naturally resilient to heat and drought, allowing it to thrive.
IMPLICATIONS FOR FOREST MANAGEMENT
The research used long-term field data from the USDA Forest Service’s inventory program. It provided an unprecedented look at how tree populations are shifting in real-time rather than theoretical projections.
“Dr. Nigro’s work is essential in understanding how climate, fire, and insects interact to shape forests,” said co-author Kristen Pelz. “This knowledge is vital for future forest management.”
FUTURE FORESTS MAY LOOK DIFFERENT
Rather than studying average tree range changes, this research examined the shifting cold and warm margins of species’ ranges. These details offer actionable insights for forest managers. If trees were naturally expanding into cooler areas, assisted migration wouldn’t be as critical.
“Land managers need to decide whether to hold onto trees in warming zones or transition to more heat-tolerant species,” Nigro said. Assisted migration might include planting seeds of the same species but adapted to warmer conditions.
THE PATH FORWARD
Nigro’s ongoing research at the Rocky Mountain Research Station explores which tree seeds have the best survival odds in changing climates. Meanwhile, co-author Miranda Redmond continues studying tree species adaptations at UC Berkeley.
“The rapid pace of climate change means we need proactive strategies,” Redmond said. “Tree die-offs from wildfires, drought, and other disturbances are increasing, making regeneration failures more common.”
A CALL FOR ACTION
Without intervention, forests in the U.S. West may struggle to regenerate. Assisted migration may be necessary to preserve tree populations where they provide ecological and economic value.
“We may need to accept that future forests will look different,” Nigro concluded. “Some areas will inevitably change, but we can take steps to guide that transformation.”
