every year, at In early November, one of the most impressive natural spectacles in the world takes place in Michoacán, Mexico. Hundreds of millions of migrating monarch butterflies take up residence in the forested massifs of the country’s Monarch Butterfly Biosphere Reserve, about 100 kilometers west of Mexico City. After flying south for eight months, starting their journey in the northern United States or southern Canada, they hibernate here for the winter before mating in the spring.
After flying more than 4,000 kilometers, the butterflies land in the oyamel fir trees of the Ejido el Rosario region, where they gather for weeks, protecting themselves from the wind and cold nights. Without these trees, the butterflies would not be able to survive their exhausting journey.
The Oyamel fir grows in a very small, humid but cold climate space. “Its distribution is very limited to the highest mountains of central Mexico,” says Cuauhtémoc Sáenz Romero, a professor at the Universidad Michoacana de San Nicolás de Hidalgo. Sáenz Romero is the lead author of a recent study that predicts that this forest will gradually deteriorate until it disappears due to climate change, endangering butterflies.
For roosting monarchs, the oyamel canopy serves as a buffer for local temperature and humidity, explains Sáenz Romero. “During the day, in the shade of the oyamel, the environment remains 5 degrees cooler than outside. It is a protection against high temperatures. At night the opposite occurs, with the result that the environment is 5 degrees Celsius warmer.” The density of the canopy also protects from winter rain. “If the temperature drops below freezing and the butterflies get their wings wet, they can freeze. This is why these trees represent such a particular habitat,” explains Sáenz Romero.
After awakening from hibernation and mating in central Mexico, the insects fly north to Texas, United States, where they lay their eggs. “For all this they need energy reserves to return, which they do not have to spend fighting the cold in their wintering sites,” he explains.
This fine balance for their survival is provided only by oyamel firs. However, some models indicate that the favorable climate in this area will disappear by 2090. “Due to rising temperatures, we are observing a process of forest decline,” says Sáenz Romero, who is leading an initiative to create new sites of wintering. for monarchs, which are on the red list of threatened species.