Geoscientist Receives Grant to Track Climate Change Through Tree Rings

Photo by Russell Cothren

David Stahle.

FAYETTEVILLE, Ark. ­­– University of Arkansas researchers have received a grant to develop the first multicentury tree-ring chronologies in the Amazon River basin to help build a historical record of climate change in one of the most ecologically diverse areas on Earth.

David Stahle, a Distinguished Professor in the U of A Department of Geosciences, will lead the three-year project. Song Feng, a professor in the Department of Geosciences who studies climate modeling and change, is the project’s co-researcher. The work is funded by a $418,000 grant from the National Science Foundation.

“The Amazon River is the largest on Earth and supplies some 17 percent of all freshwater input to the global oceans,” says Stahle. “The most extensive tropical rainforests in the world are found in Amazonia, but little is known about climate change in the region.”

Though the Amazon Basin plays a critical role in global weather patterns, its climatological history is relatively short. Rainfall and river discharge there have only been gauged for about a century. Limited as they are, the data show extreme variability in the last 20 years. Two of the most severe droughts on record occurred in 2005 and 2010, and 2013 saw record floods in the western Amazon.

The cause of these recent extremes is a mystery, but the hypothesized explanations include deforestation in the Amazon region, global climate change and increased water-vapor transport from the tropical North Atlantic.

By studying tropical species of trees, Stahle hopes to lengthen the Amazon’s climate record by up to three centuries, enough to determine whether extreme variability is unusual, or a recurring pattern.

“Were decade-long droughts common in the Amazon during prehistory? Probably not, but we don’t know,” he said.

Stahle plans extensive field research in Brazil in early 2016. He’ll be aided by researchers from a Brazilian university and the federal government, and by scientists from Argentina. One tree species he will concentrate on is Bertholettia excelsa, the famous Brazil nut tree. This species is suitable for research because it is widespread and exhibits annual growth rings. Stahle and his colleagues will examine huge cross sections of Brazil nut, and other hardwoods, that have been salvaged from logging associated with the construction of the Belo Monte Dam on the Rio Xingu. These cross sections are valuable because they can be used to develop the master dating chronology for the eastern Amazon, and subsequent research can be based entirely on non-destructive core samples.

Stahle has done similar research throughout North America, extending the record of growing season drought and wetness by centuries. In a study published last year, Stahle was part of a team that reconstructed drought conditions over Mexico during 22 typhus epidemics of the colonial and early modern era.

About the University of Arkansas: The University of Arkansas provides an internationally competitive education for undergraduate and graduate students in more than 200 academic programs. The university contributes new knowledge, economic development, basic and applied research, and creative activity while also providing service to academic and professional disciplines. The Carnegie Foundation classifies the University of Arkansas among only 2 percent of universities in America that have the highest level of research activity. U.S. News & World Report ranks the University of Arkansas among its top American public research universities. Founded in 1871, the University of Arkansas comprises 10 colleges and schools and maintains a low student-to-faculty ratio that promotes personal attention and close mentoring.