Like every year, at the beginning of November one of the most impressive natural spectacles in the world took place in Mexico: the settlement of monarch butterflies in the mountainous region in the center of the country. After their birth in the northern United States and southern Canada, every fall hundreds of millions of them fly along the forested massifs of the Monarch Butterfly Biosphere Reserve, on the border between the states of Michoacán. and the State of Mexico, its hibernation habitat.
After making a journey of more than 4,000 kilometers, the butterflies land explosively in the fir trees of the Rosario ejido, where for weeks they gather to protect themselves from the wind and the night cold. These sacred fir trees are biomes that function as important carbon sinks, in addition to serving as a refuge for hundreds of species of animals, plants and fungi. Without them, monarchs would not be able to survive their exhausting migratory journey.
The fir tree grows in a very small climatic space, in a humid and cold place. “But, not too much. “Its distribution is very limited to the highest mountains in central Mexico,” explains Cuauhtémoc Sáenz Romero, professor at the Universidad Michoacana de San Nicolás de Hidalgo and lead author of a study published in Frontiers in Forests and Global Change which anticipates that this forest will gradually deteriorate to the point of disappearance, endangering the survival of the butterflies.
As the biologist, one of the greatest Mexican specialists in forest genetic improvement, explains, the fir tree crown constitutes an extraordinary temperature and humidity buffer system for the monarch butterfly. “During the day, under the shade of the fir tree, the environment remains 5ºC colder than outside. It is protection against high temperatures. At night it happens the other way around, resulting in 5ºC warmer.” In addition, the density of the canopy of these trees acts as protection against winter rain. “If the temperature drops below zero and the butterflies get their wings wet, they can freeze. That is why these trees represent such a particular habitat,” reveals the biologist. After mating in central Mexico, the insects take the route back to Texas, United States, where they lay their eggs. “For all this, they need energy reserves to return that they should not spend on fighting the cold in their winter stay places,” he clarifies.
This very fine balance for their survival is provided only by the fir trees, known as sacred trees. However, some climate change models indicate that the favorable climate habitat for them will disappear by 2090 in the Monarch Reserve. “Due to the increase in temperatures we are observing a process of forest decline,” says Sáenz Romero, who leads an initiative to establish new hibernation sites for monarch butterflies, which are on the red list of threatened species.
Hibernating monarch butterflies in the El Rosario Monarch Butterfly Biosphere Reserve, in Michoacan, Mexico.Sylvain CORDIER/Getty Images
Plant forests for butterflies
To contribute to its conservation, since 2017, Sáenz Romero has been carrying out a pioneering experiment: demonstrating the viability of planting new fir forests in a volcano near the Monarch Butterfly Biosphere, in the Nevado de Toluca, an area This is of higher altitude and also serves as a Protected Natural Area in the mountainous region of the Transversal Neovolcanic Axis of Mexico. “As temperatures and dryness increase, trees become stressed and weakened. So, the bark beetle, a natural and common pest for these trees, has a more powerful impact, attacking more trees with more success,” explains Sáenz Romero, with more than 20 years of experience in the conservation of the coniferous forests of Michoacán. . The specialist is also the author of another study that, since 2012, already predicted this scenario for the habitat of the fir trees and its rebound effect on the butterflies. “This is a death announced in two stages,” he points out. First the weakening of the tree occurs due to dry and hot weather, then the plague arrives that finishes them off.
Faced with this dramatic situation that, as a consequence, may endanger the survival of butterflies, together with the indigenous community of Calimaya, State of Mexico, the scientific team led by Sáenz Romero is working to create new forests outside their current geographical area. The idea is to “use assisted migration to establish new sacred fir forests on the colder slopes of the mountains, where monarch butterflies could be offered much-needed refuge,” explains the researcher.
This is a project that in no way could have started without the indigenous community involved. “They understand that their work involves a positive effort for their forest. In addition, they have a great sense of attachment to their territory and a lot of ecological knowledge. They know where and when to collect the seeds, how to remove the plant from the root ball, make the vine, compact the soil. “This knowledge is the product of accumulated wisdom, of a close relationship with the territory,” says the scientist.
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