Plants in Mesoamerican cloud forests climb mountains to escape climate change

Plants are also seeking to escape climate change. So much so that in the cloud forests of Mesoamerica, a place where the landscape is shrouded in mist, plant species have moved between 1.8 and 2.7 meters per year since 1979. The climate at the altitude where they had lived for decades was no longer suitable for them and, like any animal or human looking for a new refuge in the face of a disturbing change, plants have very slowly begun to climb the mountains.

“It is an important sign that the ecological impacts of this crisis are more complex than we think,” warns Santiago Ramírez Barahona, the lead author of the study that reached this conclusion and that was chosen to be the cover story on the March print edition of the journal Science. Together with several colleagues and with funding from the Mexican Secretariat of Science and Technology, the team has been seeking to understand the vulnerability of cloud forests to climate change since 2019. These figures are the latest piece to be added to a puzzle that they are beginning to put together.

From Mexico to Panama, cloud forests represent just 1% of the surface area, “although this figure is for what existed before the 20th century; now it may be much less,” Ramírez explains. In that small percentage, however, there are more than 6,000 species of vascular plants, that is, 18% of the plant diversity in the entire region. Despite their overwhelming prevalence, less than 20% are protected. In Mexico, adds Angela Cuervo from the National Autonomous University of Mexico (UNAM) and co-author of the article, “these forests are one of the most fragile ecosystems.”

The problem, as is the case throughout Latin America and the Caribbean, is that there is little data on the ground that provides clues about how trees are moving. Ideally, countries would have a tree census that records how species are moving every five, 10 or 20 years. But since this is not the case in Mesoamerica, researchers had to come up with their own methods.

The first thing, the researchers say, was to think about what data they needed. After months of browsing through various options, they decided to use information from the Global Biodiversity Information Facility, a global repository fed by scientists from around the world, which records the name of the species they find as well as the coordinates and the year in which they documented it. Thus, they downloaded the indicators of the region collected over the last 30 years.

They then combined this information with elevation and relief data from satellite images, and created a timeline of how 1,021 plants in the cloud forests of Mesoamerica have moved. Their conclusion was that around 380 species (36%) have moved to higher altitudes to escape the new conditions brought on by both climate change and deforestation.

The changes in climate conditions are trapping the most sensitive plants. They cannot go down, because for some it is already too hot. And even if they start to move, the risk is that they will not survive in colder areas either. On the other hand, sometimes they are also threatened by deforestation.

Furthermore, not all species behave in the same way. “What has made me think the most is that only a third, and not all, plants are moving,” says Ramírez. The researcher makes a curious but pedagogical similarity to what happens with a multitude of cockroaches when a light is turned on. Each one runs off in a different direction, in survival mode. The difference is that the relationship between one species of plant and another, or its interaction with the bushes or ferns with which they have symbiosis, has been forged to reach a perfect balance for thousands of years. And climate change is breaking that.

“It could be understood as a disintegration of the forest, which, even in human terms, would cease to function, because many of these ecosystems provide us with water,” says the biologist. In fact, he remembers the times he has visited the cloud forests. Their humidity is so powerful that, while outside the forest it may not be raining, you need only peek inside their trees to feel the drizzle falling.

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