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. 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. Newscom

By Pete Spotts, Staff writer
January 21, 2011 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. 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. … [T]he 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. … Over the 70-year span between data sets, California’s average temperature has risen 0.6 degrees Celsius (1 degree Fahrenheit). Some 72 percent of the species migrated downhill during that time, compared with 28 percent marching uphill. When the team looked for explanations, they found that the plant species appeared to be extending their habitat downhill to altitudes where water is more prevalent, even in the face of an additional, slight increases in the temperatures their new, lower locations presented. Over the 70-year span, these species averaged a downhill slide of about 85 meters (278 feet), the team estimates. One factor contributing to the slow, downhill march – at least along the coast – “could be temperature changes that make the fog come in further, so that downhill ends up being a little cooler,” says Kathryn Thomas, a plant ecologist with the US Geological Survey who is based on Portland, Ore.
Whatever the mix of drivers, the results suggest the potential that different organisms that currently rely on each other could end up going their separate ways, to the detriment of both, Dobrowski says. “You can envision, for example, a situation in which you have insects moving upslope, because they are more tightly linked to temperature, and vegetation moving downslope” because of its thirst for water. In effect, pollinators would move upslope while the plants they pollinate head the other direction. …

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