Some European Grasslands May Resist Warming

John Roach, National Geographic News 7 Jul 08;

Grassland ecosystems found in higher altitudes throughout Western Europe may be resistant to climate change, according to new results from a long-term experiment.

The finding is in sharp contrast to similar research conducted in an alpine meadow in North America that suggests mountain wildflowers will all but disappear in a warming world.

Other studies have also shown major climate-spurred changes to plant composition in Minnesota bogs, Alaskan forests, and Siberian tundra.

But the new study found very little change in a European grassland even after 13 years of controlled exposure to higher temperatures and shifting rainfall patterns.

"It's taken a long time to recognize that some systems may be rather more resistant [to climate change] than those that were reported on earlier," said lead study author Philip Grime, an ecologist and emeritus professor at the University of Sheffield in England.

Grime and colleagues describe their work in a paper published online today in the journal Proceedings of the National Academy of Sciences.

Simulated Warming

Between 1994 and 2006, Grime's team monitored 97-square-foot (9-square-meter) plots in a grassland in Buxton, England, normally used for grazing livestock.

Each plot was trimmed to simulate continued grazing but was kept 5.4 degrees Fahrenheit (3 degrees Celsius) warmer than nearby outside temperatures.

The team also manipulated rainfall patterns to mimic the droughts and deluges anticipated in a warming world.

Initially the scientists saw an increase in some shrubs and a decrease in flowering plants such as rockroses and wild thyme due to the simulated droughts.

Otherwise, not much has happened to species composition at their research sites.

Grime and colleagues think that one of the reasons for the grassland's resilience is that many of the species are long-lived. Some have leaves, for example, that have adapted to the vagaries of shifting weather.

"They have a capacity over a very short time to adjust the internal physiology of their cells," Grime explained. This helps them to resist frost in the winter and drought in the summer.

In addition, recent research has shown that many of the plant species are genetically diverse at the local scale. So even if a spike in temperatures one year kills some individual plants, the survivors will be robust enough to repopulate the area.

"Each plant will have winners and losers, but the net effect will be that the individual species—most of them—tend to survive," Grime said.

What's more, he added, the limestone soil underneath the grassland is patchy. Soils are deep in some places, shallow in others; some drain well after heavy rains, others do not.

This combination of factors should keep the grasslands intact for years to come even in the face of global warming, the team says.

"We think this is a quite complex, multifaceted resistance mechanism," Grime said.

While similar grasslands were once common throughout Europe, most have long since been converted to crop fields, Grime noted.

Today conservationists are keen to protect the remaining grasslands because they are home to many uncommon species.

Rarities at Buxton include a small fern known as the green spleenwort and the stemless thistle, Grime said.

In fact, the Buxton experiments suggest that agriculture and other land uses will be bigger threats to such ecosystems than climate change.

Atypical Response?

John Harte is an ecosystem sciences professor at the University of California, Berkeley, who was not involved in the Buxton research.

Harte and colleagues have heated an alpine meadow in the Rocky Mountains for 18 years to simulate climate change and study its effects.

In the meadow, shallow-rooted forbs such as wildflowers "were hammered by the heating," Harte said. Shrubs such as sagebrush, meanwhile, have thrived.

Harte said grazing may be a key factor in the Buxton grassland's resilience.

His former graduate student Julia Klein is now working on the Tibetan Plateau, where she has found that simulated grazing reduces the effect of warming on plant productivity and species composition when compared to a nongrazed plot.

This could be because grazing keeps shrubs, which would thrive in warmer climates, from expanding and taking over the grasslands.

"It's wonderful that they've found a system that is relatively resilient," Harte said of the Buxton research site. "But I don't think its representative of the world's ecosystems."

A more typical response to climate change, Harte said, will be extinctions and major shifts in the dominant plant species.

Understanding exactly what such ecosystems will look like is "almost impossible," he added.

"I'm beginning to believe now that it's a lot easier to solve global warming than predict its consequences."