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Plants' global warming dilemma: climb to escape heat or stoop for water?

For years researchers have watched plants and animals migrate to cooler quarters in response to global warming. But a new study suggests some plants are moving downhill, drawn by increased precipitation.

By Staff writer / January 21, 2011

It was long thought that plants move to higher ground and to higher latitudes as the Earth warms, but new research has found that plants are also moving to lower elevations to be closer to snow, rain, and fog as a result of global warming.

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For years, scientists have recorded the gradual march of plants and animals up mountain slopes and toward higher latitudes as global warming has forced them to chase their climatic comfort zones.

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A new study suggests that for plants, however, a warming climate can send them downhill as well – a result several researchers say has important implications for efforts to conserve the biological richness of mountain habitats in the face of long-term global warming.

Other researchers have noted that plants can buck the general trend toward relocating at higher altitudes. But the travels often were attributed to a mix of potential factors, ranging from land-use changes to unique reactions by individual species of plants to warming.

The new study, published in the Jan. 21 issue of the journal Science, suggests that the availability of moisture – snow, rain, or fog, for instance – may override some plants' response to temperature, at least for a while, drawing them down to altitudes where more moisture is available.

At first blush, the tendency of plants to follow the water might seem obvious to any backyard gardener raising potatoes or petunias.

But in the context of global warming, the focus has tended to fall on temperature's influence on plants, rather than precipitation's, researchers say. The reason is that the researchers have higher confidence in climate models' temperature projections than they do in precipitation projections.

Indeed, the new study grew out of a desire to provide a reality check to the ecological models used to explore the possible effects global warming could have on the distribution of plants and animals, says Solomon Dobrowski, a forest ecologist at the University of Montana at Missoula.

Dr. Dobrowski and graduate student Shawn Crimmins led the team conducting the work. The study covers mountain regions that embraces roughly half the state of California. It includes the entire expanse of the state's coastal ranges north of Santa Barbara, crosses east through the southern Cascades in northern California, then reaches south along the length and breadth of the Sierra Nevada range.

Detailed data on California

Dobrowski picked California because the state hosts remarkably detailed and geographically comprehensive information on the state's plant and animal ranges gathered by naturalist Albert Wieslander during the 1920s and 30s. Few places have such rich historical information to draw on, Dobrowski says.

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