Every year, millions (but perhaps billions) of monarch butterflies make their autumnal journey to the oyamel fir forests and hilly terrain of the Monarch Butterfly Biosphere Reserve northwest of Mexico City.
56,259 hectares in size, the reserve is a safe haven for the species, after enduring a formidable migration from Canada and the United States every winter.
However, as rising temperatures, droughts, and disease threaten this sanctuary — by 2090, the reserve’s habitats are expected to deteriorate, and with them, the monarchs — scientists are desperate to find a new home for the orange winged-beauties.
On the slopes of the Nevado de Toluca volcano, about 80 miles away from the current biosphere, scientists are creating that new home — and helping the oyamel fir forests migrate there, too.
The technique is aptly called “assisted migration,” and would ideally situate the forest at a higher elevation to protect the species they house.
“We’re doing something different,” Dr. Cuauhtémoc Sáenz-Romero, a researcher at the Universidad Michoacana de San Nicolás de Hidalgo in Michoacán, told National Geographic.
“If we don't do this, the trees in the monarch reserve are going to die.”
While natural areas like forests do move naturally, changing directions and elevations over time, they do not move as quickly as climate change.
To help, the scientists are collecting seeds from a place with a specific climate — the monarch’s reserve — and moving them to an area that would have a similar climate in the future.
“Desperate times call for desperate measures,” Karen Oberhauser, a conservation biologist at the University of Wisconsin–Madison, told Science News, about these efforts.
“If we don’t help organisms move around, you know, we’re just going to lose a lot of ecosystems.”
Oberhauser is not involved in this particular project, an experiment that began in 2017 when Sáenz-Romero and team began moving seeds from the reserve to a nursery at 9,800 feet of altitude to help them adjust.
In 2021, local Indigenous community members helped plant the seedlings on the northeast slope of the volcano, staggering them at four different altitudes and planting them under protective “nurse plants.”
Six years later — in 2023 — scientists found that at two of those altitudes (11,800 and 12,400 feet, respectively), nearly 70% of those fir seedlings had survived.
They now had proof — to accompany their hope — that assisted migration could be a solution.
Sally Aitken, a professor in Forest and Conservation Sciences at the University of British Columbia, was not part of this assisted migration study but has done her own field tests to move endangered tree species in Canada.
“These types of experiments are tremendously important,” she told National Geographic, but cautioned: “We can’t implement these as solutions unless we know they’re solutions.”
Moving a tree outside of its normal growth range could damage the individual trees, of course, but it could also have unintended ecological consequences for the other species in that ecosystem.
Some skeptics also worry if the butterflies will be able to find their new homes, should the oyamel fir trees thrive in their new environment.
But Sáenz-Romero said the butterflies are already seeking new, colder sites to settle in. On the Nevado de Toluca volcano, the temperature is one degree Celsius colder than the same elevation in the monarch’s existing reserve.
While the future of the monarchs remains to be seen — and Sáenz-Romero emphasizes that their current reserve must remain protected — he hopes this latest research convinces more stakeholders to consider the new potential of assisted migration.
He concluded in his research: “These planted stands could ultimately serve as overwintering sites for the monarch butterfly under warmer climates.”
Header image courtesy of Rafael Saldaña (CC BY 2.0)
