Alpine plants fight for turf as temperatures rise

When alpine plants are confronted by plants native to lower elevations, their survival rate declines by more than half. Above: Spring pasqueflower (Pulsatilla vernalis). (Credit: Apollonio Tottoli/Flickr)

Rising temperatures are forcing wild animals and plants to escape the heat by moving into new habitats at higher elevations.

For alpine plants, this means that they may soon be facing competition from species that have previously been unknown to them: plants forced to migrate north due to climate change.

In a warmer future climate, plant species from middle altitude (red) could migrate uphill (light red) and settle above the tree line where plants from there are pushed to the peak region (blue). (Credit: Adrian Michael/Wikimedia commons)

For a new study, researchers conducted an experiment on the Calanda, near Chur, Switzerland, and discovered that alpine plants can survive a climate that’s three degrees warmer—provided they compete with their current alpine neighbors.

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However, when alpine plants are confronted by plants native to lower elevations, their survival rate declines by more than half. Even those that did hold up against the competition grew poorly and flowered less.

“This is important because it shows that we need to know what plants are competing against if we want to predict their performance and location after climate warming,” says Jake Alexander, a plant ecologist at ETH Zurich.

The most significant competition is the one for light: Plants from lower elevations grow taller and their leaves are often larger, allowing them to out-compete smaller alpine species.

Originally, ecologists assumed that higher temperatures would prove to be alpine plants’ downfall. However, the new study, published in the journal Nature, suggests changing species interactions are more important than the direct effects of temperature after climate warming.

Fierce competition

“The decisive factor that will make life difficult for alpine plants in future is competition, and competition from novel low elevation migrants in particular,” Alexander says.

For the study, researchers tested the role of new competitors in the field. For most habitats, scientists simply don’t know which species will face each other in the future.

“But in mountains we do—the future competitors of alpine plants are only hundreds of meters down the slope,” says Professor Jonathan Levine.

Researchers transplanted four characteristic plant species—spring pasqueflower, alpine kidney vetch, glossy scabious, and black plantain—from their current location in an alpine meadow to a new home 600 meters (1,968 feet) lower down the mountain.

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This move simulated the expected rise of about 3 degrees in average temperature for Switzerland over the next 50 to 100 years. The plants were transplanted either into vegetation native to the low elevation site—their future new competitors—or into vegetation brought down from the alpine meadow—their current competitors.

Then, the scientists did the same in reverse: they moved lower plants to higher elevations.

The design let the researchers test various scenarios. First, they tested the scenarios in which alpine plants remain at their location in a warmer climate and are either invaded by species from lower elevations, or remain competing with their current alpine community.

Second, they tested the scenarios in which the alpine plants manage to migrate upwards, where they encounter high-alpine plant communities or their current competitors that migrate along with them.

The overriding effect of new competitors under warmer climactic conditions isn’t a big surprise, but is important for efforts to predict species’ climate change responses, researchers say.

“The vast majority of predictions about where species will be in the future is based on the assumption that competitor identity doesn’t matter,” says Jeff Diez, now professor at the University of California, Riverside.

“Finding out that it is competition from lower-elevation flora that serves as the decisive effect, and not higher temperatures as previously assumed, is a very valuable discovery,” Alexander says.

Source: ETH Zurich