"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.
The study is likely to add urgency to a decades-long movement to protect the state's flora. The California Native Plant Society, which has 33 chapters, warns that less than 10% of the state's original coastal sage-scrub land and less than 1% of its native grassland remain intact.
But the paper foresees even more dramatic changes. Coast redwoods may range farther north, it said, while California oaks could disappear from Central California in favor of cooler weather in the Klamath Mountains along the Oregon border. Many plants may no longer be able to survive in the northern Sierra Nevada or in the Los Angeles Basin.
It also predicts that plants of northern Baja California will migrate into San Diego County ranges. Meanwhile, the Central Valley could become the preferred habitat for plants of the Sonoran Desert.
And what would replace Southern California's native plants? "We don't know what will move into the void," Loarie said. "Possibly desert plants similar to those in Nevada and Arizona, but more likely unpleasant agricultural weeds."
Coauthor Katharine Hayhoe, a Texas Tech University scientist who serves on the United Nations' 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 study looks at eight scenarios that used different rates of warming and of species mobility. Loarie cautioned that there were 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.
"But there is a clear trend," he said. "The climate is outpacing these plants."
