In a paper published today in the journal Science, a University of California, Davis, researcher and his co-authors challenge a widely held assumption that plants will move uphill in response to warmer temperatures.

Between 1930 and 2000, instead of colonizing higher elevations to maintain a constant temperature, many California plant species instead moved downhill an average of 260 feet, said Jonathan Greenberg, an assistant project scientist at the UC Davis Center for Spatial Technologies and Remote Sensing.

“While the climate warmed significantly in this period, there was also more precipitation. These wetter conditions are allowing plants to exist in warmer locations than they were previously capable of,” Greenberg said.

Many forecasts say climate change will cause a number of plants and animals to migrate to new ranges or become extinct. That research has largely been based on the assumption that temperature is the dominant driver of species distributions. However, Greenberg said the new study reveals that other factors, such as precipitation, may be more important than temperature in defining the habitable range of these species.

The findings could have global relevance, because many locations north of 45 degrees latitude (which includes the northernmost United States, virtually all of Canada and Russia, and most of Europe) have had increased precipitation in the past century, and global climate models generally predict that trend will continue, the authors said.

“As we continue to improve our understanding of climate-change impacts on species, we will help land managers and policymakers to make more informed decisions on, for instance, conservation efforts for threatened and endangered species,” Greenberg said.

He added that the study underlines the importance of an investment in basic science, as the results are based on historical data collected by the U.S. Forest Service in the 1930s, a program that was supported by New Deal spending after the Great Depression.

The study is titled “Changes in climatic water balance drive downhill shifts in plant species’ optimum elevations.” Greenberg’s co-authors are: graduate student Shawn Crimmins (the lead author), assistant professor Solomon Dobrowski (a UC Davis alumnus) and research analyst Alison Mynsberge, all of the University of Montana; and assistant professor John Abatzoglou of the University of Idaho.

Funding was provided by the U.S. National Science Foundation and the U.S. Forest Service.