Ascending Plants

Ascending Plants Photo Credit: Clipart.com

Plants are gradually moving to higher altitudes to escape global warming.


Plants head for the hills. I'm Bob Hirshon and this is Science Update.

Some people go to the mountains to beat the heat. Now, French and Chilean scientists report that plants are permanently moving to higher altitudes to escape global warming.

They studied 171 plant species in six European mountain ranges, from sea level to 8500 feet above it. Jonathan Lenoir of the AgroParisTech Institute says that on average, the plant species have climbed almost 100 feet per decade since 1970, when temperatures started rising sharply. But they're not all moving at the same rate, which complicates the picture.


Because if some species move faster than others, you may dismantle plant communities and thus you may change habitats.

And those fractured habitats may be inhospitable to local animals, as well as the plants themselves. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

As climate change heats up the world's ecosystems, many species of plants and animals, from songbirds to whales, are leaving their time-tested home ecosystems for uncharted territory. Some seek refuge from harsh, new environmental conditions; others go in search of food sources that have disappeared from their old homes.

In very broad, simple terms, when you want to move to a cooler place, you can do one of two things: move to a different latitude—away from the warm equator and toward the cooler poles—or move to a higher altitude, since mountain habitats are generally cooler than those closer to sea level. (Of course, there are plenty of exceptions to these rules; for example, Rome, Italy, is closer to the North Pole than New York City, but Rome has a warmer climate, thanks to ocean currents from the tropics.)

So far, most studies of species migration have focused on changes in latitude, but this one looked at changes in altitude—in plant species, no less, which obviously can't just pick up and walk to a new habitat. As you heard, they found that on average, the plant species they studied are living about 100 feet higher than they were in 1970. In the earlier part of the 20th century, the plant species were already moving up, but much more slowly. The rapid change in altitude of the past few decades parallels a sharp increase in global temperatures over the same period. With global temperatures rising faster by the day, we can only expect the trend to continue.

It's easy to look at this study and think: So what? Who cares if the plants around the Swiss Alps are moving to higher elevations? While it's true that this particular trend may not affect your life in the slightest, there are several reasons to care. First, we're not just talking about mountain ecosystems getting some pretty new flowers. The plants that are arriving at one elevation also are leaving another. What they leave behind includes animals and other species that may depend on the plants to survive. If the plants go, it could set off a domino effect that affects every other part of that ecosystem.

Secondly, introducing a new species to an ecosystem often creates problems of its own. The new species may crowd out or out-compete the plants that have existed in that habitat for years. Again, that would change life drastically for the other species in the ecosystem. On the other hand, the new plant could be poorly adapted to the new ecosystem and die out altogether. Furthermore, the fact that species aren't changing altitude at the same rate suggests that mountain ecosystems may soon trade stable, time-tested webs of interdependence for crazy, quilt-patchwork collections of species that haven't evolved together and can't support each other in a sustainable way.

Finally, the consequences of climate change don't occur in a vacuum. The climate of the entire globe is interconnected in the same way that the world's ecosystems are interconnected. If plant species are fleeing from sea level in Europe, they're probably doing the same around mountain ranges worldwide, which means they're changing the lower-altitude ecosystems that they leave behind, and the other ecosystems connected to those abandoned habitats, and so on. And specific findings like this represent just one of the countless ways in which human-induced climate change is rapidly altering the planet.

Now try and answer these questions:

  1. What is the difference between latitude and altitude? How have species responded to climate change in terms of latitude and altitude?
  2. Why is it significant that most of the change in altitude among plant species has occurred since 1970?
  3. Suppose, instead, that the study found that plants have been shifting gradually upwards in altitude at a steady rate over the past thousand years. How would you interpret those results?
  4. What are the possible consequences of a species abandoning one ecosystem and invading another?

You may want to check out the September 5, 2008, Science Update Podcast to hear further information about this Science Update and the other programs for this week. This podcast's topics include: antifreeze from fleas, silk optics for food safety, plants head for the hills, heavy metals that won't go away, and more.

For Educators

In the National Geographic Xpeditions student activity Creative Climates, students explore the world's diverse climate zones and find out how climate affects human life.

Several National Geographic News articles describe how climate change threatens ecosystems like U.S. National Parks, the Bering Sea, and Antarctica.

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