A squirrel at the Yosemite National Park in California ... headed for higher ground.

Credit: U.S. Fish & Wildlife Service

Related articles

• Birds can't keep up with climate change
• U.N. to issue grim climate impact warming
• Origin of species mostly in the tropics
• Climate makes profound mark on ecosystems
• Tropics expanding since 1979: climatologists

WASHINGTON: Global warming is driving tropical plant and animal species to higher altitudes, potentially leaving lowland rainforest with nothing to take their place, ecologists argue in this week's issue of Science.

In a rare study on the impact of global warming in the tropics, University of Connecticut ecologist Robert Colwell and colleagues worked their way up the forested slope of a Costa Rican volcano to collect data on 2,000 types of plants and insects.

Uphill shift

"Half of these species have such narrow altitudinal ranges that a 600-metere uphill shift would move these species into territory completely new to them," said a summary of their article.

Many species would be unable to relocate at all, as most tropical mountainside forests have become "severely fragmented" by human activities.

Tropical lowland forests – the warmest on Earth – would meanwhile be challenged by the absence of replacement species. Flora and fauna unable to move uphill could also perish, unless it turns out they they can bear higher temperatures, said the study.

"Only further research can estimate the risk," the summary of the research added, "but Colwell's report indicates that the impact of global climate change on some tropical rainforest and mountain species could be significant."

In another article, Science reports this week on a similar uphill trek by squirrels, mice and other small mammals in Yosemite National Park in California, one of the oldest wilderness parks in the United States.

Comparing a landmark 1918 study against fresh data about Yosemite's wildlife numbers, it found that small mammals have moved to higher altitudes, or reduced their ranges, in response to warmer temperatures.

"We didn't set out to study the effects of climate change," said Craig Moritz, a zoologist and integrative biology professor at the University of California, Berkeley, who led the study.

Yosemite survey

"But the most dramatic finding in the Yosemite transect was the upward elevational shift of species," he said. "When we asked ourselves what changed, it hit us between the eyes – the climate."

While such population movements have not altered Yosemite's biodiversity, Moritz's research team felt that rapid changes to the climate in less than a century could be a problem, a summary of the article said.

While half of the small mammal species at Yosemite have shifted their ranges, the other half has not. That means wildlife communities – and the way in which species interact – have changed, the summary explained.

If such change happens too fast, said James Patton, a member of the study, "elements of the (ecosystem) may start to collapse because a keystone element gets pulled out too quickly".

The study used as its starting point a detailed 1918 survey of Sierra Nevada wildlife by a Berkeley professor, when the snow-capped mountain range was under threat from gold mining and overgrazing.