SAN LUIS OBISPO -- A Cal Poly, San Luis Obispo biology professor helped to complete a study showing that two-thirds of California's roughly 2,300 species of native plants could be wiped out across much of their geographic ranges by the end of the century because of rising temperatures and changing rainfall patterns.
Professor Charles Knight collaborated on the research led by University of California at Berkeley ecologist David Ackerly and included the participation of scientists from around the country.
Climate scientists have found that plants respond to rising temperatures induced by global warming by climbing to the cooler climates of higher elevations. The movement can be north or south, depending on the geography.
Knight said that San Luis Obispo County's plant life could potentially see dramatic changes -- though that depends on how severe climate changes are.
In the most optimistic scenario, under which governments move rapidly to decrease greenhouse gas emissions globally, and plant species prove able to move into new habitats, diversity might increase in the northern and coastal regions of the state, the study concluded.
But even under this scenario, many species would disappear from Southern California and the northern Sierra.
And in a more severe global warming projection, local plants would move north or to cooler climates of mountain ranges. Researchers say they can't predict the fate of any specific species.
"In my lifetime, to see these kinds of changes is very dramatic," Knight said. "I'm worried about individual species going extinct."
Co-author Katharine Hayhoe, a Texas Tech University scientist who also serves on the U.N. Intergovernmental Panel on Climate Change, prepared projections under a scenario of a relatively rapid rise in global temperature of 3.8 to 5.8 degrees Celsius by the end of the century, and under a conservative estimate of 2.3 to 3.3 degrees Celsius.
The estimates were based on lower and higher carbon dioxide emissions.
Knight said that blue oak and ceanothus are two examples of species that grow locally that could move to mountain climates and spread north into southern Oregon. Both now populate a range from Baja California to Chico.
The local professor started collaborating with Ackerly on the project five years ago when Knight studied under him as a graduate student at Stanford University.
The study, published Tuesday in the online journal PLoS One, is the first to analyze the effect of climate change on all of the plants unique to one of the world's most biologically diverse areas.
Previous models have focused on fewer species in areas such as the eastern United States, Europe, South Africa and Australia.
The scientists' work focused on nearly 600 of the most-studied native plants, including the live oak, blue oak, scrub oak, California bay, whiteleaf manzanita and the San Francisco wallflower.
They used computer models and scenarios with different rates of warming as well as of species mobility.
But they cautioned against uncertainties in the analysis, such as the known range of individual plants, the precise microclimate each plant prefers, and the magnitude of predicted changes in rainfall patterns.
Under the worst-case scenario, plant diversity would decrease everywhere by as much as 25%, and 66% of all species unique to California would suffer more than an 80% decrease in range.
If plants were able to move rapidly in the next 100 years, they would have to move an average of up to 95 miles to keep up with changing climate. The plants could move in different directions, potentially breaking up familiar California native plant associations, the authors said.
Half of the plant species that are unique to the continental United States grow only in the Golden State, from towering redwoods to slender fire poppies.
As California's unique species migrate, they could be separated from the creatures that pollinate them. Animals could be divided from the plants on which they depend, the researchers noted.
"Individual plants can't pick up and fly away like birds," Ackerly said. "A seed grows into a tree. Then the adult tree drops another seed, which can be carried by the wind or an animal. And that seed grows into another tree."
The state may also have to set aside new refuges and corridors, and prepare to move some plants if necessary.
"Planning for plant refugees will become a new but important concept for natural reserves to think about," said biologist Brent Mishler, director of the University and Jepson Herbaria at UC Berkeley, the state's most important flora collection.