They said changes in climate arising from heat-trapping greenhouse gasses would affect hundreds of native plant species including the state's famed Coast Redwoods, which are among the tallest trees on earth.

"Many species may have to move to cooler areas in order to survive," climate scientist Katharine Hayhoe of Texas Tech University, one of a team of researchers whose work appears in the Public Library of Science journal PLoS ONE, said in a statement.

"In some of these cases, for example when a plant grows near the top of a mountain, there's nowhere to go," Hayhoe said.

The researchers tracked 5,500 plants native to California and used computer models to predict how climate change would affect their distribution.

They concluded that a warming climate and changes in rainfall would force many plants to range north or to higher elevations or possibly become extinct in the next 100 years.

"We found the extent of climate change impact can be very broad," Hayhoe said in a telephone interview.

"In two-thirds of the 5,500 plants we studied, the area where you can find them shrank by 80 per cent," Hayhoe said.

She said about 40 per cent of the plants they studied exist only in California. "Preserving them is very important."

They predict Coast Redwoods would be forced farther north, while California oaks might disappear from central California in favor of the Klamath Mountains along the California-Oregon border.

The researchers used two different climate models that predict changes in temperature and rainfall through 2100 to make their projections -- one that assumes higher and another that assumes lower greenhouse gas emissions.

"In nearly every scenario we explored, biodiversity suffers -- especially if the flora can't disperse fast enough to keep pace with climate change," Scott Loarie, a Ph.D candidate at Duke University, said in a statement.

What the models did suggest, however, is that reducing greenhouse gases would have a significant impact on native species, Hayhoe said. And it pointed to steps conservationists could take to preserve California's native species.

"We were able to identify some specific locations that are refuges where these plants would be able to survive," Hayhoe said. "That helps us to plan ahead to protect these important plant species."

Brent Mishler of the University of California, Berkeley said conservationists will need to keep in mind what plants are at risk of becoming plant refugees. "Planning for refugees will become a new but important concept for natural reserves to think about," he said in a statement.

Maps showing the impact of climate change on California's plant species are available here . The article can be downloaded from the PLoS ONE Web site here.