every year at At the beginning of November, one of the most impressive natural spectacles in the world takes place in Michoacán, Mexico. Hundreds of millions of migrating monarch butterflies settle in the forested mass of the national Monarch Butterfly Biosphere Reserve, about 100 kilometers west of Mexico. After eight months of flying south, starting their journey in the northern United States or southern Canada, they hibernate here for the winter and begin mating in the spring.
After traveling more than 4,000 kilometers, the butterflies land on the oyamel fir trees in the Ejido el Rosario region, where they gather for weeks, sheltering from the wind and icy nights. Without these trees, the butterflies would not be able to survive their exhausting journey.
The oyamel fir grows in a very tiny climatic space, damp and at the same time icy. “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 main author of, among others, recent research predicts that this forest will gradually degrade until it completely disappears as a result of climate change, endangering butterflies.
For hanging out monarchs, the oyamel canopy acts as a buffer against local temperature and humidity, explains Sáenz Romero. “During the day, in the shade of the oyamel, it is 5 degrees Celsius cooler than outside. Provides protection against high temperatures. At night, the opposite is true, making the environment 5 degrees Celsius warmer.” The density of the canopy also protects against winter rain. “If the temperature drops below freezing and butterflies get their wings damp, they can freeze. That’s why these trees represent such a special habitat,” says Sáenz 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 energy reserves that they do not have to spend on fighting the icy in wintering areas,” he explains.
Only oyamel firs provide this perfect balance for their survival. However, some models indicate that the climate favorable to them in this area will disappear by 2090. “Due to rising temperatures, we are observing a process of forest disappearance,” says Sáenz Romero, who leads the initiative to establish fresh wintering places for monarchs that are in red list endangered species.