Plants in North America are spreading through the mountains faster than thought

From Mexico to Canada, mountain plants move upslope to cooler heights. In some mountain ranges, uplift reaches 112 meters per decade.

In the face of climate change, mountain plants in western North America are expanding to higher, cooler altitudes faster than previously thought. But in some regions, the ascent has not kept pace with rising temperatures.

As climate change causes global temperatures to rise, plants and animals that have evolved to live in a particular set of environmental conditions are forced to quickly adapt to new norms. One way for species to deal with heat is to move higher in altitude, where cooler conditions are maintained in a thinner atmosphere. Ecologists already knew that species respond to changes in their environment, says James Kellner of Brown University in Rhode Island. “The question is to what extent? And are they able to keep up?

To learn more about the rate of vegetation change, Kellner and colleagues compared NASA Landsat satellite imagery of nine mountain ranges in western North America between 1984 and 2011.

“Here we are talking about an absolutely huge region of the world, stretching from southern Mexico to the Canadian Rockies,” says Kellner.

When the researchers looked at peak “greenness” of mountain slopes – a measure of vegetation cover at the height of the growing season – they found a rapid change: Plants were rising an average of 67 meters higher per decade – more than four times as fast. than previously reported. In New Mexico, where vegetation moved fastest, plants rose more than 112 meters in a decade.

Warming is not the only reason vegetation can move upslope. Changes in precipitation patterns or environmental disturbances such as agriculture, grazing, and fires can also cause skyward drift. But Kellner says finding this pattern across different mountain ranges points to one common factor: rising temperatures.

“It’s hard to think of any explanation for this. [pattern] besides being constantly working in nine mountain ranges between Mexico and Canada,” says Kellner. Climate change has also affected the amount and timing of rainfall in some regions, but the pattern has not been consistent in all regions.

The fast ascent of some plants may not be fast enough. When the team compared the measured upslope shear rates of five U.S. mountain ranges with what would be predicted by recent warming, only plants in two ranges – in New Mexico and the Sierra Nevada – are keeping up with climate change.

“If species are pushed out of range where they can have viable, sustainable populations,” Kellner says, “then we could be in a situation where we lose them.”

According to Sabine Rumpf from the University of Basel in Switzerland, the time span of almost three decades analyzed and the geographic range are the main strengths of the study. But because the study looks at land cover as a whole, Basel says the results can’t tell us what’s going on with individual plant species.

“The problem is that species change in different ways. [from one another] “There is a huge variation.” She says the results are “a wake-up call that species are already on the move.”