Report: Plants Follow Water Downhill, Not Just Higher Temperatures Uphill

Thursday, January 20 2011

Written by Bill Loftus
MOSCOW – Climate change may allow plants to expand downhill as precipitation increases in addition to expanding uphill as temperatures rise, a University of Idaho geographer says.

John Abatzoglou, an assistant professor of geography at Moscow, is among co-authors of a report in the current issue of Science magazine that shows plants in California’s Sierra Nevada and coast range have responded to changes in precipitation and temperature.

The report counters the widely held notion that plants will be forced uphill by rising temperatures. These findings suggest that species response to anticipated changes in climate might be less dire than predicted earlier.

The report by University of Montana forestry researchers Shawn Crimmins, Solomon Dobrowski and Alison Mynsberge, and Jonathan A. Greenberg of the University of California at Davis examined the distribution of 64 species of plants in central and northern California.

Increases in precipitation in California during the 20th century have outpaced increases in evaporation caused by warming, and this has led to increased water availability across the northern half of the state. The change allowed many plants to shift downhill into areas where water availability was previously limiting.

While Abatzoglou said that the 1 degree Fahrenheit warming observed across California during the last century was attributable to human-caused changes in climate, the increase in precipitation and water availability likely reflects natural climate variability, not human-caused changes.

While their study focused on California, Abatzoglou said, "This work may help us understand how predicted human-caused changes at higher latitudes may affect plants."

Predictions of a warmer Earth include local shifts in moisture. At higher latitudes, beginning about the 45th Parallel, or in Idaho from about New Meadows east to Salmon, changes in weather patterns are expected to bring slightly more precipitation.

Increased precipitation is some areas may balance increased evaporative demand due to warming, allowing some plants to maintain their current elevation rather than moving exclusively uphill to adapt to warmer temperatures, Abatzoglou said.

"One thing that can trump all of this of course are disturbance events like wildfire and beetle attack, which could significantly modify the pace of climate-induced vegetation response," Abatzoglou said.

Economically important trees like Douglas fir and ponderosa pine, he said, did not appear likely colonize valleys but held more closely to present habitats according to the team's analysis.

Many plants that provide important grazing and wildlife habitat did move lower as shifts in moisture occurred.

The team looked at vegetation surveys in California from 1930-35 and 2000-2005 to track changes in plant distributions, then analyzed climate records.

Abatzoglou, whose expertise is weather and climate, focused on changes in temperature and precipitation patterns. The surveys 70 years apart reflected both changes in moisture during those years, and a two-decade long dry spell in California immediately before the earliest plant surveys.

Most climate change researchers predict widespread extinction and range shifts for hundreds of plant and animal species. Abatzoglou said, "The findings of this study should force us to reconsider temperature as the sole driver and instead include multiple factors that affect species distributions."
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About the University of Idaho
Founded in 1889, the University of Idaho is the state’s land-grant institution and its principal graduate education and research university, bringing insight and innovation to the state, the nation and the world. University researchers attract nearly $100 million in research grants and contracts each year. The University of Idaho is the only institution in the state to be classified by the prestigious Carnegie Foundation as high research activity. The student population of 12,000 includes first-generation college students and ethnically diverse scholars, who select from more than 130 degree options in the colleges of Agricultural and Life Sciences; Art and Architecture; Business and Economics; Education; Engineering; Law; Letters, Arts and Social Sciences; Natural Resources; and Science. The university also is charged with the statewide mission for medical education through the WWAMI program. The university combines the strength of a large university with the intimacy of small learning communities and focuses on helping students to succeed and become leaders. It is home to the Vandals, and competes in the Western Athletic Conference. For more information, visit