Every year, In early November, one of the world’s most impressive natural spectacles takes place in Michoacán, Mexico. The forested mountain massifs of the country’s Monarch Butterfly Biosphere Reserve, about 100 kilometers west of Mexico City, are home to hundreds of millions of migrating monarch butterflies. They fly south for eight months, starting their journey in the northern United States or southern Canada, where they hibernate before mating in the spring.
After flying more than 4,000 kilometers, the butterflies land on oyamel fir trees in the Ejido El Rosario region, where they congregate for several weeks, sheltering from the wind and cold nights. Without these trees, the butterflies would not be able to survive the exhausting journey.
Oyamel fir grows in a very small climatic space that is humid but cold. “Its distribution is very limited to the highest mountains of central Mexico,” says Cuauhtemoc Sáenz Romero, a professor at the University of Michoacana de San Nicolas de Hidalgo. Sáenz Romero is the lead author of a recent study that predicts that as a result of climate change, this forest will gradually degrade and disappear, putting butterflies at risk.
Sáenz Romero explains that for roosting monarch butterflies, the oyamel canopy acts as a buffer against local temperature and humidity. “During the day, under the shade of an oyamel tree, the environment remains 5 degrees Celsius cooler than outside, providing protection from high temperatures. At night, the opposite is true, resulting in an environment 5 degrees Celsius warmer.” The density also protects from winter rain. “When temperatures drop below freezing and the butterfly’s wings get wet, they can freeze. That’s why these trees represent a special habitat,” says Saenz Romero.
After emerging from hibernation and mating in central Mexico, the insects fly north to Texas in the United States, where they lay their eggs. “For all this, they need reserves of energy to return home without having to spend it fighting the cold in their wintering grounds,” he explains.
This delicate balance for survival is provided only by the oyamel fir. However, some models suggest that the region’s climate suitable for forests will disappear by 2090. “Due to rising temperatures, we are observing a process of forest decline,” said Saenz Romero, who is leading the effort to establish new wintering grounds. As for the monarch butterfly, which is on the red list of endangered species.
(Tag translation) Science
