Thermal inversion favors forests that are more resistant to warming

April 19 () –

While mountain tops are colder than the valleys below, a new study from the University of Vermont flips the script on what we know about forests and climate.

The study, published in Ecology and Evolution, explores forests that experience “cold air accumulation,” a phenomenon in which cold air at higher elevations drains into lower valleys, reversing expected temperatures: warm at the bottom, cold at the top. This usually happens in mountainous areas. That is, the air temperature drops when descending from a mountain to a valley.

“With temperature inversions, we also see vegetation inversions“, says the study's lead author and former UVM postdoctoral researcher, Melissa Pastore, in a statement. “Instead of finding more cold-preferring species, like spruces, at high elevations, we found them at lower elevations, “just the opposite of what we expected.”

And the effect on these ecosystems is substantial: “This accumulation of cold air is fundamentally structuring the forest,” says study co-author and UVM professor Carol Adair.

This idea “can help forest managers prioritize and protect areas with frequent, strong accumulations of cold air to preserve cold-loving species as the climate warms,” ​​Adair says. it's a statement.

Researchers looked at three forested sites in New England, ranging from the shallow, crater-shaped Nulhegan Basin of Vermont's Northeast Kingdom to the highest peaks and deepest valleys of the Green Mountains, over two years. They collected data on the types of trees present in the elevation transects and monitored temperature every hour.

Researchers found that, far from being the occasional nocturnal seasonal phenomenon it was historically thought to be, cold air accumulation occurs frequently, year-round, well into daylight, Adair says. The phenomenon occurred in all the sites they studied, but it was strongest at the site with the shallowest elevation change.

Places that experience this phenomenon could prove essential to conservation efforts aimed at preserving cold-adapted species even as the overall climate warms, Pastore says. “These areas of cold air accumulation could be valuable targets for small areas that provide refuge from climate change; they are areas that could be protected or even decoupled from climate change, and they host cold-adapted species that we know are vulnerable.” He adds that conserving such places can provide enough time for species to adapt to climate change, either by migrating or mixing genes with neighbors to take on the traits necessary to survive in a warmer world.

In this way, says Pastore, “These pockets of cold habitat can act as springboards for some species, they can buy them that time.”

Conservation of such places can also have practical applications, Adair says, “including carbon storage and small-scale recreational opportunities,” adding that cold-loving coniferous tree communities tend to store more carbon than deciduous trees. , and forest soils can also retain moisture longer, important during periods of extreme rainfall.

Cold air buildup has been observed historically and anecdotally elsewhere, Adair says, but this study is the first to quantify it to this degree at many sites under the forest canopy, and further research is planned to explore its temporal and geographical extent.

The accumulation of cold air is not a panacea, warns Pastore. These forests “are still warming; I definitely don't want to say they are completely safe havens, because climate change will happen there too,” but it could be slower, and perhaps species that might otherwise disappear in a warmer climate will remain. more time in these places.

The research is highly relevant in a changing climate, as ecologists seek to model what may happen to species that require cold conditions. “If you don't have this process in your model,” says Adair, “you will miss that there are areas where cold-loving species can and do persist.”

The work has been a hopeful change of pace, says Adair. “I'm excited that in some ways this is good news. These areas may help cold-adapted species persist.” He adds: “A lot of my research tells people why bad things happen, so this is good. It's not all good news, but it's some good news. These places exist. We can use them. They're important. “They are clearly structuring forests.”