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Agency Biographies

Dr. Chavonda Jacobs-Young

Under Secretary for Research, Education, and Economics and USDA's Chief Scientist

Dr. Chavonda Jacobs-Young serves as the Under Secretary for Research, Education, and Economics (REE), and as USDA’s Chief Scientist. The REE mission area is comprised of more than 8,500 employees with a $4 billion budget across its five component organizations including the Agricultural Research Service (ARS), Economic Research Service (ERS), National Agricultural Statistics Service (NASS), National Institute of Food and Agriculture (NIFA), and Office of the Chief Scientist (OCS). Together these organizations advance agricultural research, innovation, data, and Extension across a full range of agricultural issues including climate-smart agriculture, nutrition security, equity, and strengthening food supply chains. As Chief Scientist, Dr. Jacobs-Young advises the Secretary of Agriculture and other senior officials on scientific matters and chairs the USDA Science Council, which convenes all parts of USDA’s scientific enterprise.

Prior to being appointed by President Biden to serve as the REE Under Secretary, Dr. Jacobs-Young was Administrator for ARS from 2014 to 2022. Prior to that role, she served as ARS Associate Administrator for National Programs, leading the research objectives of the entire Agency. She also led the Office of International Research Programs, which is responsible for ARS' liaison with its international partners. From 2009 to 2012, Dr. Jacobs-Young served as the inaugural OCS Director, where she was responsible for facilitating the coordination of scientific leadership across the Department to ensure that research supported by, and scientific advice provided to, the Department and external stakeholders were held to the highest standards of intellectual rigor and scientific integrity. She has also served as the Acting Director for NIFA and as a senior policy analyst for agriculture in the White House Office of Science and Technology Policy.

Dr. Jacobs-Young is a native of Georgia. She holds M.S. and Ph.D. degrees in Wood and Paper Science and a B.S. degree in Pulp and Paper Science and Technology from North Carolina State University. She is a graduate of American University's Key Executive Leadership in Public Policy Implementation Program, and a proud fellow of both the American Association for the Advancement of Science and the National Academy of Public Administration.

Dr. Chavonda Jacobs-Young

Dr. Simon Liu

Administrator, Agricultural Research Service

Dr. Simon Liu has served as ARS Administrator, the chief scientific in-house research agency, since January 2023.  Prior to ARS Administrator, Dr. Liu served for seven years as the Associate Administrator for Research Management and Operations.

He previously served as Director of the National Agricultural Library (NAL), which serves as the central library for the U.S. Department of Agriculture and is one of the four National Libraries of the United States. NAL is world's largest and most accessible research library specializing in agriculture.

Before joining NAL, Simon Liu served as Associate Director of the National Library of Medicine (NLM) and Director of the NLM Computer and Communications System. Prior to his service at NLM, he held leadership positions with the U.S. Departments of Justice and Treasury, following work in the private sector where he led information system development and space mission studies to support NASA mission and operations.

He attended university in his native Taiwan and pursued graduate studies in the United States, where he earned master's degrees in Computer Science, Business Administration, and Government from Indiana University, the University of Maryland, and Johns Hopkins University. He has earned two doctoral degrees: an Ed.D in Higher Education Administration and a Ph.D. in Computer Science from George Washington University. He also serves as an adjunct faculty member with graduate school appointments at several of these institutions.

Simon Liu is active in professional societies and associations and have served as the Editor-in-Chief of an information technology magazine and editor of four journals in the past 20 years. Simon has published a book and more than 80 book chapters, journal articles, and conference papers.


Dr. Simon Liu, Administrator, Agricultural Research Service

Dr. Spiro Stefanou

Administrator, Economic Research Service

Spiro Stefanou is the Administrator of the Economic Research Service. He provides leadership and guidance for the agency research, analytical, and technical operations. Since 2015, Dr. Stefanou was a Professor of Economics in the Food and Resource Economics Department at the University of Florida.

Prior to his time at the University of Florida, Dr. Stefanou was Professor of Agricultural Economics at Penn State University since 1983. 

He is a Distinguished Fellow of the Agricultural and Applied Economics Association and was a Marie Curie Senior Fellow at the University of Crete (Rethymnon, Greece), Mansholt Senior Fellow at Wageningen University (Netherlands), and Jean Monnet Fellow at the European University Institute (Florence, Italy).  He has been a visiting professor at the Institute for Advanced Studies (Vienna, Austria), and the Mediterranean Agronomic Institute (at Chania).  Dr. Stefanou has served on the editorial boards of six national and international journals. 

Dr. Stefanou received his Ph.D. in Agricultural Economics from the University of California, Davis, his M.S. in Agricultural and Resource Economics from the University of Maryland and a Bachelor of Arts in Anthropology from George Washington University.

Dr. Spiro Stefanou, Administrator, ERS

Hubert Hamer

Administrator, National Agricultural Statistics Service

Hubert Hamer has served as NASS Administrator since 2016. He brings extensive experience in all aspects of the agency’s work. Before becoming administrator, he served as director of the Statistics Division, which produces and releases more than 400 national statistical reports each year covering the agency’s crops, livestock, economic, demographic, environmental, and census programs. He also served as executive director of the NASS Agricultural Statistics Board (ASB) and executive director of the Advisory Committee on Agriculture Statistics.

From 2010 until he became head of the Statistics Division, Hamer was chair of the Agricultural Statistics Board. As ASB chair, he led the preparation and dissemination of market-sensitive reports compiled and issued under special security conditions known as Lockup. He was also responsible for promotion and outreach of the NASS mission to all stakeholders. From May 2000 until April 2010, Hamer served as associate deputy administrator for field operations, overseeing 24 state field offices as well as the Training and Career Development Office.

Since joining NASS, Hamer has served in a number of capacities in Washington, D.C. as well as the Louisiana, Illinois, and Missouri field offices. While directing the Missouri office, he completed USDA’s Senior Executive Candidate Development Program and was appointed to the Senior Executive Service in 2000. Hamer completed the program for Senior Managers in Government at Harvard University’s John F. Kennedy School of Government in 2004 and completed the Office of Personnel Management (OPM) Executive Potential Program in 1994. As part of the OPM program, he served as a fellow with the Senate Budget Committee and worked on the staff of the Secretary of Agriculture.

Hamer was born on a small livestock and row crop farm in Benton County, Mississippi, and later continued his development in Grand Junction, Tennessee. He is a graduate of Tennessee State University.


Hubert  Hamer

Dr. Dionne Toombs

Acting Director, National Institute of Food and Agriculture

Dr. Dionne Toombs is the Acting Director of the National Institute of Food and Agriculture, the U.S. Department of Agriculture’s extramural grant funding agency for agricultural research, education, and Extension programs across the nation. Previously, she was Director of the Office of the Chief Scientist, where she led a wide range of issues affecting science programs and science policy in agricultural research, education, and economics. 

Dr. Toombs also provided scientific leadership and coordination to the White House, Office of Science and Technology Policy, National Science and Technology Council working groups, across USDA and other federal agencies, and the agricultural community. 

With over a decade of USDA service, Dr. Toombs was the Division of Nutrition at NIFA where she led USDA nutrition science leaders who helped steer science policy and program development to ensure America’s food supply is safe, nutritious, and accessible to all citizens. She was the National Program Leader for NIFA’s Agriculture Food and Research Initiative, leading large competitive grant programs to fund research into nutrition, food science and technology, and food safety and as a Program Specialist for Food Science and Nutrition at the former USDA Cooperative State Research Education and Extension Service, which is now NIFA. 

Since she started at USDA as a student intern at USDA’s Agricultural Research Service, Dr. Toombs has been repeatedly featured as one of USDA’s most impactful woman scientists and recognized by the Secretary of Agriculture for outstanding leadership. Throughout her career, she has helped her colleagues, staff, and students maximize their potential by bolstering their talents and developing their leadership skills. Always willing to champion the next generation of scientists, she often emphasizes the importance of relationship building, citing collaboration as a key to her success. 

Dr. Dionne Toombs

Dr. Deirdra Chester

Acting Director of the Office of the Chief Scientist

Dr. Deirdra Chester serves as the Acting Director of the Office of the Chief Scientist (OCS), where she leads collaboration activities for science programs that support scientific excellence, innovation, and capacity to achieve USDA’s mission. She provides leadership on a wide range of issues affecting programs in agricultural research, education, and economics. In her permanent position, she serves as the Division Director of the Division of Nutrition at NIFA’s Institute of Food Safety and Nutrition. In this role, she provides leadership and oversight for the division’s research, education, and extension activities across the nation through competitive grant programs.

Previously, Dr. Chester was the agency Science Advisor for USDA’s Animal and Plant Health Inspection Service (APHIS). Before APHIS, she served as the National Program Leader for NIFA’s Applied Nutrition Research in the Division of Nutrition at the Institute of Food Safety and Nutrition Prior to joining NIFA, Dr. Chester was a scientist at USDA’s Agricultural Research Service.

Additionally, Dr. Chester is a Registered Dietitian/Nutritionist. She has spoken both nationally and internationally on nutrition topics and is on the editorial board of the Journal of Obesity and Chronic Disease.

Dr. Chester is a graduate of the American University Key Executive Leadership program and is SES certified through the USDA Senior Executive Service Candidate Development Program. Dr. Chester holds a Doctor of Philosophy in nutrition from Florida International University, where she was awarded the McKnight Doctoral Fellowship and was in the inaugural class of the Gates Millennial Scholars. She holds a master’s in food and nutrition science and a bachelor’s degree in nutrition and dietetics from Florida State University.

Dr. Chester is the recipient of numerous honors and awards. The American Public Health Association Food and Nutrition Section awarded her the Mary C. Egan Award and she was recognized by Florida State University’s College of Human Science with the Circle of Excellence Alumni Award.


Dr. Deirdra Chester