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As a California high school student, Jamie Wright thought her family’s finances meant that college was out of reach. Now, the UO graduate student is the lead author of a paper that provides a reference map covering 1,600 years of human and climate impacts on soil in the Amazon.
His project, carried out as a member of Co-author Lucas Silva of the Soil Plant Atmosphere Research Lab, details vegetation changes and carbon isotope signatures in the soil at 83 sites in the transition zones of forest and savannah. The study was published online Oct.31 ahead of print in the journal Global Change Biology.
“The past, like most things, leaves a trace behind it and with it a rich history left to tell,” Wright said. “Through the use of soil science, particularly with carbon isotopes, we have unearthed a history of forest expansion over several millennia. This region is the epicenter of deforestation and the socio-ecological transformations that cause and drive climate change. “
The forest-savannah border areas, known as the Amazon-Cerrado transition, are undergoing extensive climatic and ecological influences. The study addressed uncertainties related to those influences in the tropical ecosystem, said Silva, professor in the Environmental Studies Program, Department of Geography and Institute of Ecology and Evolution.
“Our data indicates a regional increase in tree cover before modern deforestation, which could help inform conservation and management for climate change mitigation,” said Silva. “We hope our research will lead to a greater appreciation of ecological processes in the region and their importance for global climate stability.”
Previous research had suggested that forest expansion was primarily driven by increased rainfall, but that work, Silva noted, did not fully consider local influences, such as the frequency and intensity of fires or whether it was occurring due to of climatic dynamics. Focusing on soil changes, he said, made it possible to examine these factors.
“Carbon storage in wooded savannahs and large-scale forest plants can be a significant carbon sink,” Wright said. “Increasing tree cover can also improve adverse impacts of climate change, such as drought, by affecting the hydrological cycle and generating rain clouds.”
In total, 742 soil samples were taken from forests, savannas and transitional areas in a wide swath of north-central Brazil, between latitudes 4 to 16 degrees south and longitudes 46 to 56 degrees west, a ‘ area where rainfall and distribution vary significantly.
The researchers also measured the forest canopy leaf index to understand changes in soil carbon isotope signatures. These changes reflect land use. To determine changes over time, radiocarbon activity and isotope ratios were profiled in 43 selected depths.
The research was co-led by Barbara Bomfim, a former postdoctoral researcher in Silva’s lab now at Lawrence Berkeley National Laboratory. Other team members were researchers from Boston College and Mato Grosso State University in Nova Xavantina, Brazil.
The team is continuing to work with collaborators in the Amazon region in an effort to secure funding to launch a reforestation project that could help weather the storm of climate change, Silva said.
For Wright, who is pursuing a PhD in environmental science, studies and politics in the OU’s environmental studies program, the ongoing research is the continuation of his interest in climate-related issues that began when he was in high school in Woodland, California, northwest of Sacramento.
“When I was 16, I never thought I’d go to college, but I joined a program that linked college students with high school kids to conduct a science experiment related to climate change,” he said. “Eventually I continued on this path, got to college and stayed true to environmental science.”
From the University of California, Davis, Wright earned a bachelor’s degree in environmental science and management, focusing on soil science and biogeochemistry. Upon her arrival at the OU, Silva offered her the opportunity to work in the Amazon.
“I was all in,” he said.
The National Science Foundation and the Brazilian National Council for Scientific and Technological Development funded the research. Additional support came from a 2019 Resilience Initiative Interdisciplinary Seed Funding Award awarded by the Office of the OU’s Vice President for Research and Innovation.
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