Plants "Climbing" Mountains Due to Global Warming

Mason Inman
for National Geographic News
June 26, 2008
Like people vacationing in the mountains to escape summer heat, plants are "climbing" to higher elevations to cope with global warming, a new study shows.

Previous research has suggested that many plant and animal species have been shifting their ranges toward the Poles as the planet warms.

(Read related news: "Wild Holly, Mistletoe, Spread With Warmer Winters" [December 7, 2005].)

Now scientists have found evidence that plants have also been slowly moving into higher elevations to stay within ideal temperature zones.

Each year this "escalator effect" is pushing plants upward by about ten feet (three meters).

"When we started to look at this, I was not expecting such a strong message," said study leader Jonathan Lenoir, a forest ecologist at AgroParisTech, a research institute in France.

If global warming continues over the coming decades—as researchers predict it will—the plants will continue to climb. (Explore an interactive map of the effects of global warming.)

But since some species move faster than others, this shift could tear established ecosystems apart, the researchers report in tomorrow's issue of the journal Science.

Moving on Up

For more than a century naturalists all over the world have been recording exactly where they found various plant species in the mountains.

"Botanists used to wander in mountain ecosystems … to look for and study specific mountain plant communities, to locate rare and endangered plant communities … or even simply to enjoy the landscape within mountains," Lenoir said.

In the mountains climate conditions change dramatically with altitude, making it is easier to detect when certain species shift to higher elevations.

"Mountains are [therefore] amazing places to observe vegetation changes in response to climate warming," Lenoir added.

The new study drew on nearly 8,000 historical surveys of the mountains in and around France, some stretching back to 1905.

Temperatures in these mountains—which include the Western Alps, Pyrenees, and Massif Central—crossed a threshold around 1985, the researchers say.

Before that year the region shows no clear trend in climate changes. But since then the mountains have been warming, and plants began moving in sync with rising temperatures.

The scientists looked at the movements of 171 species in forests on the lower slopes, from sea level up to 8,500 feet (2,600 meters).

While earlier studies had focused on plants in high altitudes that are known to be more sensitive to temperature changes, the new work found that even common plants at lower elevations are feeling the heat.

The team also discovered that different types of plants are moving at different rates.

"Long-lived plants like trees or shrubs did not show a significant shift, whereas short-lived species like herbs showed a strong upward shift in elevation," Lenoir said.

"This may imply profound changes in the composition and the structure of plant communities and on the animal species they interact with," he added. "It may disrupt ecosystems."

Out of Room

Steven Running is an ecologist at the University of Montana in Missoula who was not involved in the new study.

"Theory would predict that warming temperatures will allow plant distributions to expand into cooler, higher mountain elevations," he said.

"This paper confirms the theory. With a large population analysis, [it is] the best evidence published so far that plant distributions are rising [in altitude]."

The shifts in elevations of some plants and not others "shows very much that the ecosystems are already evolving away from the ecosystems as we know them," added Cynthia Rosenzweig of the NASA Goddard Institute for Space Studies in New York City.

With shorter-lived species, "we're seeing this rapid response" to warming, Rosenzweig said.

While it shows these plants are adapting to the changes, she noted, "they're going to have to keep moving up and up—and eventually run out of room."

And the longer-lived species that aren't moving may also be headed for trouble, she said.

"There's concern that they aren't adapting and may not have spread their seeds far enough" to shift their ranges to cope with continued warming.

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